Lithium metaborate crystal, preparation method and use thereof

Abstract

The invention relates to a lithium metaborate crystal and a preparation method and use thereof. The crystal has a chemical formula of LiBO.sub.2, a molecular weight of 49.75, and is a member of the monoclinic crystal system. The crystal has a P2.sub.1/c space group and lattice constants of a=5.85(8) , b=4.35(7) , c=6.46(6) , =115(5), and Z=4. The crystal can be applied in wavelengths of infrared-visible-deep ultraviolet, and is grown by utilizing a melt crystallization method or a flux method. The crystal obtained using the method described in the invention is easily grown and processed, and can be used in the manufacture of a polarizing beam splitting prism such as a Glan prism, a Wollaston prism, a Rochon prism or a beam-splitting polarizer, and other optical components, enabling crucial applications in the fields of optics and communication.

Claims

1. A method for preparing the lithium metaborate crystal, wherein said method is a melt method or a flux method, and said melt method comprises the steps of: a-1) mixing and grinding a lithium-containing compound and a boron-containing compound in a molar ratio of 1:1 to obtain a first mixture; placing the first mixture into a corundum crucible and pre-heating the first mixture at 300 C. for 8 hours; increasing the temperature by 100 C. five times, until 800 C., wherein the first mixture is kept for 8 hours at each temperature, and is subject to grind and compaction at the each temperature after being kept for 8 hours, and when the temperature reaches 800 C., the first mixture is held at temperature of 800 C. for 3-5 days; and obtaining polycrystalline powder of lithium metaborate compound; b-1) placing the polycrystalline powders of lithium metaborate into a platinum crucible; alternatively, mixing and grinding the lithium-containing compound and a boron-containing compound in a molar ratio of 1:1 to obtain a second mixture and placing the second mixture directly into the platinum crucible; heating the polycrystalline powders or the second mixture to 600-900 C. and holding the polycrystalline powders or the second mixture at temperature of 600-900 C. for 1-50 hours, to form a melt mixture, wherein the lithium-containing compound is Li.sub.2O, LiOH, Li.sub.2CO.sub.3, LiNO.sub.3, CH.sub.3COOLi, or Li.sub.2C.sub.2O.sub.4, and said boron-containing compound is H.sub.3BO.sub.3 or B.sub.2O.sub.3; c-1) preparing lithium metaborate seed crystal, wherein the temperature of the melt mixture obtained from step b-1) is reduced by 5-10 C., and the melt mixture is kept for 2-6 hours at each temperature; the temperature reducing and holding process is repeated until a floating crystal is observed on the surface of the melt mixture; then the temperature is slowly decreased at a rate of 0.5-10 C./d until crystallization is completed; after that, the temperature is reduced at a rate of 10-50 C./h to room temperature, and the lithium metaborate seed crystal is obtained; d-1) placing the platinum crucible that contains the melt mixture obtained from step b-1) into a crystal growth furnace, fixing the lithium metaborate seed crystal obtained from step c-1) to a seed rod, decreasing the temperature of the crystal growth furnace to 560-850 C., and placing the rod into the hearth from the top of the crystal growth furnace; thereafter preheating the lithium metaborate seed crystal for 1-30 minutes above a surface of the melt mixture and then moving the lithium metaborate seed crystal down to or beneath the surface of the melt mixture for remelting; keeping the temperature for 1-20 minutes before decreasing the temperature to 550-844 C.; e-1) reducing the temperature slowly at a rate of 0.1-5 C./d, rotating the rod at a rate of 0-30 r/min, and lifting up the lithium metaborate seed crystal at a rate of 0-10 mm/h simultaneously; then lifting the lithium metaborate seed crystal out of the melt mixture when the lithium metaborate seed crystal grows into a desired size and reducing the temperature to room temperature at a rate of 5-50 C./h; thereafter collecting the lithium metaborate seed crystal from the hearth to obtain lithium metaborate crystal in centimetre-size; and wherein said flux method comprises the steps of: a-2) mixing and grinding lithium metaborate compound and flux to obtain a third mixture; placing the third mixture into a platinum crucible, heating the third mixture to 600-900 C. and keeping the third mixture at temperature of 600-900 C. for 1-50 hours, to generate a mixed solution containing flux, wherein a molar ratio of lithium metaborate and the flux is 1:(0.01-4); or, mixing and grinding the lithium-containing compound, boron-containing compound and flux in a molar ratio of 1:1:(0.01-4) to generate a fourth mixture containing flux, placing the fourth mixture into a platinum crucible, heating the fourth mixture to 600-900 C. and keeping the fourth mixture at temperature of 600-900 C. for 1-50 hours, to generate a mixed solution containing flux; wherein the lithium-containing compound is Li.sub.2O, LiOH, Li.sub.2CO.sub.3, LiNO.sub.3, CH.sub.3COOLi or Li.sub.2C.sub.2O.sub.4; the boron-containing compound is H.sub.3BO.sub.3 or B.sub.2O.sub.3; the flux is LiCl, LiBr, LiF, Li.sub.2O, LiOH, Li.sub.2CO.sub.3, B.sub.2O.sub.3, H.sub.3BO.sub.3, Cs.sub.2CO.sub.3, CsF, SrCO.sub.3, SrF.sub.2, Na.sub.2CO.sub.3, NaF, NaCl, KF, KCl, K.sub.2CO.sub.3 or MoO.sub.3; b-2) preparing lithium metaborate seed crystal, wherein the temperature of the mixed solution containing flux obtained from step a-2) is reduced rapidly by 5-10 C., and the melt mixture is kept for 2-6 hours at each temperature; the temperature reducing and holding process is repeated until a floating crystal is observed on a surface of the mixed solution; then the temperature is slowly decreased at a rate of 0.5-10 C./d until crystallization is completed; thereafter the temperature is reduced at a rate of 10-50 C./h to room temperature, and the lithium metaborate seed crystal is obtained; or, fixing a platinum wire to a seed rod and placing the platinum wire into the mixed solution containing flux obtained from step b-2); slowly reducing the temperature at a rate of 1-5 C./h until a crystal forms on the platinum rod; thereafter rotating the rod at a rate of 0-30 r/min, reducing the temperature at a rate of 0.1-10 C./d, and lifting the crystal out of the solution when the lithium metaborate seed crystal grows into a desired size; then decreasing the temperature to room temperature at a rate of 10-50 C./h and obtaining the lithium metaborate seed crystal; c-2) placing the platinum crucible that contains the mixed solution obtained from step a-2) into a crystal growth furnace, fixing the lithium metaborate seed crystal obtained from step b-2) to a seed rod, decreasing the temperature of the crystal growth furnace to 560-850 C., and placing the rod into the hearth from the top of the crystal growth furnace; preheating the lithium metaborate seed crystal for 1-30 minutes above the surface of the mixed solution and then moving the lithium metaborate seed crystal down to or beneath the surface of the mixed solution for remelting; holding the temperature for 1-20 minutes before reducing the temperature to 550-844 C.; d-2) reducing the temperature slowly at a rate of 0.1-5 C./d and rotating the rod at a rate of 0-30 r/min, and lifting up the lithium metaborate seed crystal at a rate of 0-10 mm/h simultaneously; then lifting the lithium metaborate seed crystal out of the mixed solution when the lithium metaborate seed crystal grows into a desired size and reducing the temperature to room temperature at a rate of 5-50 C./d; thereafter collecting the lithium metaborate seed crystal from the hearth to obtain lithium metaborate crystal in centimetre-size.

2. The method according to claim 1, wherein said melt method comprises top seeded melting method, Czochralski method, Kyropoulos method and Bridgman-Stockbarger method.

3. The method according to claim 1, wherein said lithium-containing compound and boron-containing compound have purity of 99.0%.

4. The method according to claim 1, wherein said flux has purity of 99.0%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the structure of the lithium metaborate crystal used in the infrared-visible-deep ultraviolet range.

(2) FIG. 2 shows a XRD spectrum of the lithium metaborate crystal used in the infrared-visible-deep ultraviolet range.

(3) FIG. 3 shows a photograph of the lithium metaborate crystal used in the infrared-visible-deep ultraviolet range.

(4) FIG. 4 shows a schematic diagram of the wedge-shaped birefringent crystal polarization splitter made by the lithium metaborate crystal obtained in the invention.

(5) FIG. 5 shows a schematic diagram of the beam shifter made by the lithium metaborate crystal obtained in the invention, in which 1 represents incident light 2 represents light o (ordinary light). 3 represents light e (extraordinary light), 4 represents optical axis, 5 represents LiBO.sub.2 crystal, 6 represents light direction, and 7 represents optic axial plane.

(6) FIG. 6 shows a schematic diagram of the optical isolator made by the lithium metaborate crystal obtained in the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Example 1. Growth of Lithium Metaborate Crystal by Czochralski Method

(7) Lithium metaborate crystal was produced according to the reaction formula, Li.sub.2O+2H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. The ran materials Li.sub.2O and H.sub.3BO.sub.3 used were of analytical grade (99%).

(8) Li.sub.2O and H.sub.3BO.sub.3 were directly mixed and ground thoroughly in a molar ratio of 1:1 (Li:B) before placed into a platinum crucible. The mixture was slowly heated to 900 C. and kept at this temperature for 24 hours, to form a melt mixture.

(9) Preparation of lithium metaborate seed crystal: the temperature of the melt mixture obtained as above was rapidly reduced by 5 C. each time, and held at such a temperature for 2 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the melt mixture. Then the temperature was slowly decreased at a rate of 0.5 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 10 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(10) The crucible containing the melt mixture obtained as above was placed into a crystal growth furnace, and the seed crystal obtained as above was fixed to the seed rod. The temperature was decreased to 845 C., and the seed crystal was placed into the hearth from the top of the furnace. After preheated for 5 minutes above the surface of the melt mixture, the seed crystal was moved down to the surface of the melt mixture for remelting. The temperature was kept for 1 minute before reduced rapidly to 840 C.

(11) The rod was rotated at a rate of 2 r/min and at the same time, the crystal was lifted up at a rate of 1 mm/h. When crystal began to grow, the quality of the seed crystal was further optimized by shoulder extending and necking down process. Then the lifting rate was kept at 0.5 mm/h, and the temperature was slowly reduced at a rate of 0.1 C./d. The crystal entered an equal-diameter growth process. As the crystal grew into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 10 C./h. Then the crystal, i.e., lithium metaborate crystal with a size of 261933 mm.sup.3 was obtained and collected from the hearth.

(12) The lithium metaborate crystal obtained using this method possesses high transparency. Transmission spectrum measurement showed that the crystal had a transmission range of 150-4000 nm and a birefringence of 0.08-0.28.

Example 2. Growth of Lithium Metaborate Crystal by Czochralski Method

(13) Analytically pure (99%) lithium metaborate was weighted and placed directly into a platinum crucible. Then the sample was slowly heated to 900 C. and held at this temperature for 5 hours, to form melt mixture.

(14) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to the lower part of a seed rod was placed into the melt mixture, and then the temperature was slowly reduced at a rate of 5 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 5 r/min and the temperature was slowly reduced at a rate of 2 C./d. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(15) The crucible containing the obtained melt mixture was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 845 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the melt surface. Then the seed crystal was moved down to the surface of the melt mixture for remelting. The temperature was held for 1 minute before decreased rapidly to 842 C.

(16) The rod was rotated at a rate of 4 r/min and at the same time, the crystal was lifted up at a rate of 1.5 mm/h. When crystal began to grow, the quality of the seed crystal was further optimized by shoulder extending and necking down process. Then the lifting rate was kept at 0.5 mm/h, and the temperature was slowly reduced at a rate of 0.3 C./d. The crystal entered an equal-diameter growth process. As the crystal grew into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 10 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 362947 mm.sup.3 was obtained and collected from the hearth.

Example 3. Growth of Lithium Metaborate Crystal by Top Seeded Melting Method

(17) The lithium metaborate crystal is produced on the basis of the reaction formula, Li.sub.2CO.sub.3+2H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+CO.sub.2+H.sub.2O. Raw materials Li.sub.2CO.sub.3 and H.sub.3BO.sub.3 used were of analytical grade (99%).

(18) Li.sub.2CO.sub.3 and H.sub.3BO.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and round thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C., for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 5 days; and then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(19) Then the polycrystalline powders of lithium metaborate obtained as above was placed in to a platinum crucible, heated to 900 C. and held at this temperature for 24 hours, to generate melt mixture.

(20) Preparation of the lithium metaborate seed crystal: the temperature of the melt mixture obtained as above was rapidly reduced by 10 C. and held for 6 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the melt mixture. Then the temperature was slowly decreased at a rate of 10 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 50 C./h to room temperature and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(21) The crucible containing the obtained melt mixture was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 850 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 30 minutes above the surface of the melt mixture. Then the seed crystal was moved down to contact with the surface of the melt mixture for remelting. The temperature was held for 10 minutes before decreased rapidly to 844 C.

(22) Then the temperature was reduced slowly at a rate of 5 C./d and the seed rod was rotated at a rate of 30 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 10 mm/h. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 50 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 327615 mm.sup.3 was obtained and collected from the hearth

Example 4. Growth of Lithium Metaborate Crystal by Kyropoulos Method

(23) The lithium metaborate crystal was produced on the basis of the reaction formula, LiOH+H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and H.sub.3BO.sub.3 used were of analytical grade (99%).

(24) LiOH and H.sub.3BO.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; and then polycrystalline powder of lithium metaborate compound was obtained. After X-ray analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(25) Then the polycrystalline powders of lithium metaborate obtained as above was placed in to a platinum crucible, heated to 900 C. and held at this temperature for 12 hours, to generate melt mixture.

(26) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to the lower part of a seed rod was placed into the melt mixture, and then the temperature was slowly reduced at a rate of 5 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 30 r/min and the temperature was slowly reduced at a rate of 10 C./d. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was decreased to room temperature at a rate of 50 C./h. As a result, lithium metaborate seed crystal was obtained.

(27) The crucible containing the obtained melt mixture was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 848 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 20 minutes above the surface of the melt mixture. Then the seed crystal was moved into the melt mixture for remelting. The temperature was held for 5 minutes before decreased rapidly to 842 C.

(28) Then the temperature was reduced slowly at a rate of 3 C./d and the seed rod was rotated at a rate of 15 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 5 mm/h. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 25 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 261917 mm.sup.3 was obtained and collected from the hearth.

Example 5. Growth of Lithium Metaborate Crystal by Top Seeded Melting Method

(29) The lithium metaborate crystal was produced on the basis of the reaction formula, LiNO.sub.3+H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+NO.sub.2+H.sub.2O. Raw materials LiNO.sub.3 and H.sub.3BO.sub.3 used were of analytical grade (99%).

(30) LiNO.sub.3 and H.sub.3BO.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and around thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 4 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(31) Then the polycrystalline powders of lithium metaborate obtained as above was placed in to a platinum crucible, heated to 900 C. and held at this temperature for 1 hour, to generate melt mixture.

(32) Preparation of the lithium metaborate seed crystal: the temperature of the melt mixture obtained as above was rapidly reduced by 7 C., and held for 4 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the melt mixture. Then the temperature was slowly decreased at a rate of 5 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 25 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(33) The crucible containing the obtained melt mixture was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 847 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 1 minute above the surface of the melt mixture. Then the seed crystal was moved down to contact with the surface of the melt mixture for remelting. The temperature was held for 8 minutes before decreased rapidly to 843 C.

(34) Then the temperature was reduced slowly at a rate of 2 C./d and the seed rod was not rotated (at a rate of 0/min). At the same time, the crystal was not lifted up (at a rate of 0 mm/h). As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 30 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 22169 mm.sup.3 was obtained and collected from the hearth.

Example 6. Growth of Lithium Metaborate Crystal by Kyropoulos Method

(35) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2CO.sub.3+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2. Raw materials Li.sub.2CO.sub.3 and B.sub.2O.sub.3 used were of analytical grade (99%).

(36) Li.sub.2CO.sub.3 and B.sub.2O.sub.3 were placed directly into a platinum crucible after mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was slowly heated to 900 C. and kept at this temperature for 24 hours, to generate melt mixture.

(37) Preparation of the lithium metaborate seed crystal: the temperature of the melt mixture obtained as above was rapidly reduced by 6 C., and held for 3 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the melt mixture. Then the temperature was slowly decreased at a rate of 8 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 40 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(38) The crucible containing the obtained melt mixture was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 846 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 10 minutes above the surface of the melt mixture. Then the seed crystal was moved into the melt mixture for remelting. The temperature was held for 3 minutes before decreased rapidly to 841 C.

(39) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 5 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.5 mm/h. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 10 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 362234 mm.sup.3 was obtained and collected from the hearth.

Example 7. Growth of Lithium Metaborate Crystal by Czochralski Method

(40) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(41) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 4 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(42) Then the polycrystalline powders of lithium netaborate obtained as above was placed in to a platinum crucible, heated to 900 C. and held at this temperature for 16 hours, to generate melt mixture.

(43) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to the lower part of a seed rod was placed into the melt mixture, and then the temperature was slowly reduced at a rate of 1 C./h until crystal formed on the platinum wire. Then the rod was not rotated (at a rate of 0 r/min) and the temperature was slowly reduced at a rate of 0.1 C./d. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was decreased to room temperature at a rate of 10 C./h. As a result, lithium metaborate seed crystal was obtained.

(44) The crucible containing the obtained melt mixture was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 849 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 15 minutes above the surface of the melt mixture. Then the seed crystal was moved down to contact with the melt mixture for remelting. The temperature was held for 3 minutes before decreased rapidly to 843.5 C.

(45) Then the temperature was reduced slowly at a rate of 0.1 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.5 mm/h. As growing into a desired size, the crystal was lifted out of the melt mixture and the temperature was reduced to room temperature at a rate of 5 C./h. Then, the crystal, i.e., lithium metaborate crystal in a size of 362947 mm.sup.3 was obtained and collected from the hearth.

Example 8. Growth of Lithium Metaborate Crystal by Flux Method

(46) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2C.sub.2O.sub.4+2H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+CO.sub.2+H.sub.2O. Raw materials Li.sub.2C.sub.2O.sub.4 and H.sub.3BO.sub.3 used were of analytical grade (99%).

(47) Li.sub.2C.sub.2O.sub.4 and H.sub.3BO.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 5 days; and then polycrystalline powder of lithium metaborate compound was obtained. After X-ray analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(48) Lithium metaborate compound obtained as above was mixed with the flux H.sub.3BO.sub.3(analytically pure, 99%) thoroughly in a molar ratio of 1:0.01 (LiBOH.sub.2:H.sub.3BO.sub.3), placed into a platinum crucible, heated to 860 C. and kept at this temperature for 50 hours, to generate a mixed solution containing the lithium metaborate and flux.

(49) Preparation of the lithium metaborate seed crystal: the temperature of the mixed solution obtained as above was rapidly reduced by 5 C., and held for 2 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the mixed solution. Then the temperature was slowly decreased at a rate of 0.5 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 10 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(50) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 830 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 30 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 1 minute before decreased rapidly to 820 C.

(51) Then the temperature was reduced slowly at a rate of 5 C./d and the seed rod was rotated at a rate of 30 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 10 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 50 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 161217 mm.sup.3 was obtained and collected from the hearth.

Example 9. Growth of Lithium Metaborate Crystal by Flux Method

(52) The lithium metaborate crystal was produced on the basis of the reaction formula, LiCH.sub.3COO+H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+CO.sub.2+H.sub.2O. Raw materials LiCH.sub.3COO and H.sub.3BO.sub.3 used were of analytical grade (99%).

(53) LiCH.sub.3COO and H.sub.3BO.sub.3 were weighted in a molar ratio of 1:1 (Li:B), mixed with analytically pure (99%) flux LiOH (in a molar ratio of Li:B:LiOH=1:1:1, corresponding to a molar ratio of LiBO.sub.2:LiOH=1:1) and ground thoroughly. The mixture was then placed into a platinum crucible, slowly heated to 600 C. and kept at this temperature for 10 hours, to generate a mixed solution containing the lithium metaborate and flux.

(54) Preparation of the lithium metaborate seed crystal: the temperature of the mixed solution obtained as above was rapidly reduced by 10 C., and held for 6 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the mixed solution. Then the temperature was slowly decreased at a rate of 10 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 50 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(55) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 560 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 15 minutes above the surface of the mixed solution. Then the seed crystal was moved into the mixed solution for remelting. The temperature was held for 20 minutes before decreased rapidly to 550 C.

(56) Then the temperature was reduced slowly at a rate of 3 C./d and the seed rod was not rotated (at a rate of 0 r/min). At the same time, the crystal was not lifted up (at a rate of 0 nm/h). As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 30 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 17116 mm.sup.3 was obtained and collected from the hearth.

Example 10. Growth of Lithium Metaborate Crystal by Flux Method

(57) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2O+B.sub.2O.sub.3.fwdarw.LiBO.sub.2. Raw materials Li.sub.2O and B.sub.2O.sub.3 used were of analytical grade (99%).

(58) Li.sub.2O and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 4 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(59) The lithium metaborate compound obtained as above was mixed with the flux Cs.sub.2CO.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:0.02 (LiBO.sub.2:flux), placed into a platinum crucible, heated to 760 C. and kept at this temperature for 10 hours, to generate a mixed solution containing the lithium metaborate and flux.

(60) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 1 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 5 r/min and the temperature was slowly reduced at a rate of 0.1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 10 C./h. As a result, lithium metaborate seed crystal was obtained.

(61) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 710 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 1 minute above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 15 minutes before decreased rapidly to 702 C.

(62) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 15 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 5 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 5 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 191516 mm.sup.3 was obtained and collected from the hearth.

Example 11. Growth of Lithium Metaborate Crystal by Flux Method

(63) The lithium metaborate crystal was produced on the basis of the reaction formula, LiNO.sub.3+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+NO.sub.2. Raw materials LiNO.sub.3 and B.sub.2O.sub.3 used were of analytical grade (99%).

(64) LiNO.sub.3 and B.sub.2O.sub.3 were weighted in a molar ratio of 1:1 (Li:B), mixed with analytically pure (99%) flux CsF (in a molar ratio of Li:B:flux CsF=1:1:0.1, corresponding to a molar ratio of LiBO.sub.2:CsF=1:0.1) and ground thoroughly. The mixture was then placed into a platinum crucible, slowly heated to 810 C. and kept at this temperature for 30 hours, to generate a mixed solution containing the lithium metaborate and flux.

(65) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 5 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 10 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 20 C./h. As a result, metaborate seed crystal was obtained.

(66) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 760 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 10 minutes above the surface of the mixed solution. Then the seed crystal was moved into the mixed solution for remelting. The temperature was held for 5 minutes before decreased rapidly to 750 C.

(67) Then the temperature was reduced slowly at a rate of 0.5 C./d and the seed rod was rotated at a rate of 10 r/min. At the same time, the crystal was lifted up at a rate of 3 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 15 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 211617 mm.sup.3 was obtained and collected from the hearth.

Example 12. Growth of Lithium Metaborate Crystal by Flux Method

(68) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2C.sub.2O.sub.4+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2+CO.sub.2. Raw materials Li.sub.2C.sub.2O.sub.4 and B.sub.2O.sub.3 used were of analytical grade (99%).

(69) Li.sub.2C.sub.2O.sub.4 and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 5 days; then polycrystalline powder of lithium metaborate compound was obtained After X-ray diffraction analysis, it showed that X-ray diffraction spectrum of the the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(70) The lithium metaborate compound obtained as above was mixed with the flux Li.sub.2CO.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:0.05 (LiBO.sub.2:flux), placed into a platinum crucible, heated to 780 C. and kept at this temperature for 30 hours, to generate a mixed solution containing the lithium metaborate and flux.

(71) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on the platinum wire. Then the rod was not rotated (at a rate of 0 r/min) and the temperature was slowly reduced at a rate of 5 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(72) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 730 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 8 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 10 minutes before decreased rapidly to 723 C.

(73) Then the temperature was reduced slowly at a rate of 0.1 C./d and the seed rod was rotated at a rate of 2 r/min so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 5 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature by 20 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 241711 mm.sup.3 was obtained and collected from the hearth.

Example 13. Growth of Lithium Metaborate Crystal by Flux Method

(74) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiCH.sub.3COO+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2+H.sub.2O. Raw materials LiCH.sub.3COO and B.sub.2O.sub.3 used were of analytical grade (99%).

(75) LiCH.sub.3COO and B.sub.2O.sub.3 were weighted in a molar ratio of 1:1 (Li:B), mixed with analytically pure (99%) flux LiF (in a molar ratio of Li:B:flux LiF=1:1:0.6, corresponding to a molar ratio of LiBO.sub.2:LiF=1:0.6) and ground thoroughly. The mixture was then placed into a platinum crucible, slowly heated to 800 C. and kept at this temperature for 40 hours, to generate a mixed solution containing the lithium metaborate and flux.

(76) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 5 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 30 r/min and the temperature was slowly reduced at a rate of 10 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 50 C./h. As a result, lithium metaborate seed crystal was obtained.

(77) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 755 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 20 minutes above the surface of the mixed solution. Then the seed crystal was moved into the mixed solution for remelting. The temperature was held for 3 minutes before decreased rapidly to 751 C.

(78) Then the temperature was reduced slowly at a rate of 1.5 C./d and the seed rod was rotated at a rate of 6 r/min. At the same time, the crystal was lifted up at a rate of 2 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 35 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 221917 mm.sup.3 was obtained and collected from the hearth.

Example 14. Growth of Lithium Metaborate Crystal by Flux Method

(79) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(80) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(81) The lithium metaborate compound obtained as above was mixed with the flux B.sub.2O.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:0.15 (LiBO.sub.2:flux), placed into a platinum crucible, heated to 815 C. and kept at this temperature for 48 hours, to generate a mixed solution containing the lithium metaborate and flux.

(82) Preparation of the lithium metaborate seed crystal: the temperature of the mixed solution obtained as above was rapidly reduced by 8 C., and held for 4 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the mixed solution. Then the temperature was slowly decreased at a rate of 5 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 30 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(83) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 765 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 10 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 4 minutes before decreased rapidly to 758 C.

(84) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 5 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.5 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 25 C./h. Then the crystal, i.e., metaborate crystal in a size of 181513 mm.sup.3 was obtained and collected from the hearth.

Example 15. Growth of Lithium Metaborate Crystal by Flux Method

(85) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2CO.sub.3+2H.sub.3BO.sub.3.fwdarw.CO.sub.2+H.sub.2O. Raw materials Li.sub.2CO.sub.3 and H.sub.3BO.sub.3 used were of analytical grade (99%).

(86) Li.sub.2CO.sub.3 and H.sub.3BO.sub.3 were weighted in a molar ratio of 1:1 (Li:B), mixed with analytically pure (99%) flux LiCl (in a molar ratio of Li:B:flux LiC1=1:1:0.5, corresponding to a molar ratio of LiBO.sub.2:LiCl=1:0.5) and ground thoroughly. The mixture was then placed into a platinum crucible, slowly heated to 720 C. and kept at this temperature for 24 hours, to generate a mixed solution containing the lithium metaborate and flux.

(87) Preparation of the lithium metaborate seed crystal: the temperature of the mixed solution obtained as above was rapidly reduced by 6 C., and held for 3 hours. The temperature reducing and holding process was repeated until floating crystal was observed on the surface of the mixed solution. Then the temperature was slowly decreased at a rate of 8 C./d until crystallization was completed. After that, the temperature was reduced at a rate of 5 C./h to room temperature, and lithium metaborate seed crystal was obtained by the spontaneous crystallization.

(88) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 675 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 20 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 5 minutes before decreased rapidly to 667 C.

(89) Then the temperature was reduced slowly at a rate of 2 C./d and the seed rod was rotated at a rate of 8 r/min. At the same time, the crystal was lifted up at a rate of 1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e., metaborate crystal in a size of 201216 mm.sup.3 was obtained and collected from the hearth.

Example 16. Growth of Lithium Metaborate Crystal by Flux Method

(90) The lithium metaborate crystal was produced on the basis of the reaction formula, LiOH+H.sub.3BO.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and H.sub.3BO.sub.3 used were of analytical grade (99%).

(91) LiOH and H.sub.3BO.sub.3 were weighted in a molar ratio of 1:1 (Li:B), mixed with analytically pure (99%) flux LiBr (in a molar ratio of Li:B:flux LiBr=1:1:0.3, corresponding to a molar ratio of LiBO.sub.2:LiBr=1:0.3) and ground thoroughly. The mixture was then placed into a platinum crucible, slowly heated to 810 C. and kept at this temperature for 12 hours, to generate a mixed solution containing the lithium metaborate and flux.

(92) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 4 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 25 r/min and the temperature was slowly reduced at a rate of 2 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 20 C./h. As a result, lithium metaborate seed crystal was obtained.

(93) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 765 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 15 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 3 minutes before decreased rapidly to 756 C.

(94) Then the temperature was reduced slowly at a rate of 2 C./d and the seed rod was rotated at a rate of 10 r/min. At the same time, the crystal was lifted up at a rate of 0.2 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 15 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 242118 mm.sup.3 was obtained and collected from the hearth.

Example 17. Growth of Lithium Metaborate Crystal by Flux Method

(95) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2CO.sub.3+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2. Raw materials Li.sub.2CO.sub.3 and B.sub.2O.sub.3 used were of analytical grade (99%).

(96) Li.sub.2CO.sub.3 and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(97) The lithium metaborate compound obtained as above was mixed with the flux MoO.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:4 (LiBO.sub.2:flux) placed into a platinum crucible, heated to 700 C. and kept at this temperature for 20 hours, to generate a mixed solution containing the lithium metaborate and flux.

(98) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on the platinum wire. Then the rod was not rotated at a rate of 0 r/min and the temperature was slowly reduced at a rate of 5 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(99) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 660 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 8 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 10 minutes before decreased rapidly to 653 C.

(100) Then the temperature was reduced slowly at a rate of 0.1 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.5 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 161711 mm.sup.3 was obtained and collected from the hearth.

Example 18. Growth of Lithium Metaborate Crystal by Flux Method

(101) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(102) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate-single crystal.

(103) The lithium metaborate compound obtained as above was mixed with the flux MoO.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:2 (LiBO.sub.2:flux), placed into a platinum crucible, heated to 780 C. and kept at this temperature for 20 hours, to generate a mixed solution containing the lithium metaborate and flux.

(104) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on the platinum wire. Then the rod was not rotated (at a rate of 0 r/min) and the temperature was slowly reduced at a rate of 2 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(105) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 730 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 10 minutes before decreased rapidly to 721 C.

(106) Then the temperature was reduced slowly at a rate of 0.5 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature by 20 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 14109 mm.sup.3 was obtained and collected from the hearth.

Example 19. Growth of Lithium Metaborate Crystal by Flux Method

(107) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiCH.sub.3COO+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2+H.sub.2O. Raw materials LiCH.sub.3COO and B.sub.2O.sub.3 used were of analytical grade (99%).

(108) LiCH.sub.3COO and B.sub.2O.sub.3 were weighted in a molar ratio of 1:1 (Li:B), mixed with analytically pure (99%) flux KF (in a molar ratio of Li:B:flux KF=1:1:1.5, corresponding to a molar ratio of LiBO.sub.3:KF=1:1.5) and ground thoroughly. The mixture was then placed into a platinum crucible, slowly heated to 780 C. and kept at this temperature for 40 hours, to generate a mixed solution containing the lithium metaborate and flux.

(109) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 5 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 30 r/min and the temperature was slowly reduced at a rate of 10 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 50 C./h. As a result, lithium metaborate seed crystal was obtained.

(110) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 735 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 20 minutes above the surface of the mixed solution. Then the seed crystal was moved into the mixed solution for remelting. The temperature was held for 3 minutes before decreased rapidly to 730 C.

(111) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 3 r/min. At the same time, the crystal was lifted up at a rate of 0.1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature by 30 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 12115 mm.sup.3 was obtained and collected from the hearth.

Example 20. Growth of Lithium Metaborate Crystal by Flux Method

(112) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(113) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(114) The lithium metaborate compound obtained as above was mixed with the flux KCl (analytically pure, 99%) thoroughly in a molar ratio of 1:1(LiBO.sub.2:KCl), placed into a platinum crucible, heated to 810 C. and kept at this temperature for 20 hours, to generate a mixed solution containing the lithium metaborate and flux.

(115) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 2 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 5 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(116) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 770 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 10 minutes before decreased rapidly to 740 C.

(117) Then the temperature was reduced slowly at a rate of 0.5 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e. lithium metaborate crystal in a size of 11106 mm.sup.3 was obtained and collected from the hearth.

Example 21. Growth of Lithium Metaborate Crystal by Flux Method

(118) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(119) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray difraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(120) The lithium metaborate compound obtained as above was mixed with the flux K.sub.2CO.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:0.8 (LiBO.sub.2:K.sub.2CO.sub.3), placed into a platinum crucible, heated to 790 C. and kept at this temperature for 10 hours, to generate a mixed solution containing the lithium metaborate and flux.

(121) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 3 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(122) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 740 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 5 minutes before decreased rapidly to 732 C.

(123) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.2 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 1379 mm.sup.3 was obtained and collected from the hearth.

Example 22. Growth of Lithium Metaborate Crystal by Flux Method

(124) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(125) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(126) The lithium metaborate compound obtained as above was mixed with the flux NaCl (analytically pure, 99%) thoroughly in a molar ratio of 1:0.5 (LiBO:NaCl), placed into a platinum crucible, heated to 830 C. and kept at this temperature for 20 hours, to generate a mixed solution containing the lithium metaborate and flux.

(127) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 2 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 5 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(128) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 780 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 3 minutes before decreased rapidly to 764 C.

(129) Then the temperature was reduced slowly at a rate of 0.5 C./d and the seed rod was rotated at a rate of 5 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.2 nm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e., metaborate crystal in a size of 191011 mm.sup.3 was obtained and collected from the hearth.

Example 23. Growth of Lithium Metaborate Crystal by Flux Method

(130) The lithium metaborate crystal was produced on the basis of the reaction formula, 2LiOH+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+H.sub.2O. Raw materials LiOH and B.sub.2O.sub.3 used were of analytical grade (99%).

(131) LiOH and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(132) The lithium metaborate compound obtained as above was mixed with the flux NaF (analytically pure, 99%) thoroughly in a molar ratio of 1:2 (LiBO.sub.2:NaF), placed into a platinum crucible, heated to 760 C. and kept at this temperature for 5 hours, to generate a mixed solution containing the lithium metaborate and flux.

(133) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 5 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 2 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(134) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 710 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 3 minutes before decreased rapidly to 704 C.

(135) Then the temperature was reduced slowly at a rate of 0.5 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 21119 mm.sup.3 was obtained and collected from the hearth.

Example 24. Growth of Lithium Metaborate Crystal by Flux Method

(136) Lithium metaborate (analytically pure, 99%) was directly mixed with flux Na.sub.2CO.sub.3 (analytically pure, 99%) in a molar ratio of 1:0.5 (LiBO.sub.2:Na.sub.2CO.sub.3) and ground thoroughly. Then the mixture was placed into a platinum crucible, heated to 820 C. and kept at this temperature for 8 hours, to generate a mixed solution containing the lithium metaborate and flux.

(137) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on the platinum wire. Then the rod was not rotated (at a rate of 0 r/min) and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(138) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 770 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 5 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 5 minutes before decreased rapidly to 762 C.

(139) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 30 C./h. Then the crystal, i.e., lithium metaborate crystal in a size of 18138 mm.sup.3 was obtained and collected from the hearth.

Example 25. Growth of Lithium Metaborate Crystal by Flux Method

(140) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2CO.sub.3+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2. Raw materials Li.sub.2CO.sub.3 and B.sub.2O.sub.3 used were of analytical grade (99%).

(141) Li.sub.2CO.sub.3 and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(142) The lithium metaborate compound obtained as above was mixed with the flux SrCO.sub.3 (analytically pure, 99%) thoroughly in a molar ratio of 1:0.2 (LiBO.sub.2:SrCO.sub.3) placed into a platinum crucible, heated to 760 C. and kept at this temperature for 8 hours, to generate a mixed solution containing the lithium metaborate and flux.

(143) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on die platinum wire. Then the rod was rotated at a rate of 2 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution, and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(144) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 720 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 10 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 5 minutes before decreased rapidly to 712 C.

(145) Then the temperature was reduced slowly at a rate of 1 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.1 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 30 C./h. Then the crystal, lithium metaborate crystal in a size of 191012 mm.sup.3 was obtained and collected from the hearth.

Example 26. Growth of Lithium Metaborate Crystal by Flux Method

(146) The lithium metaborate crystal was produced on the basis of the reaction formula, Li.sub.2CO.sub.3+B.sub.2O.sub.3.fwdarw.LiBO.sub.2+CO.sub.2. Raw materials Li.sub.2CO.sub.3 and B.sub.2O.sub.3 used were of analytical grade (99%).

(147) Li.sub.2CO.sub.3 and B.sub.2O.sub.3 were mixed at a molar ratio of 1:1 (Li:B) and ground thoroughly. The mixture was placed into a corundum crucible and pre-heated at 300 C. for 8 hours. After that, the temperature was increased by 100 C. each time until 800 C., during which, at each temperature, the mixture was kept for 8 hours followed by thorough grind and compaction. When the temperature reached 800 C., the mixture was held at this temperature for 3 days; then polycrystalline powder of lithium metaborate compound was obtained. After X-ray diffraction analysis, it showed that the X-ray diffraction spectrum of the polycrystalline powder obtained above was in consistent with that of the powder ground from lithium metaborate single crystal.

(148) The lithium metaborate compound obtained as above was mixed with the flux SrF.sub.2 (analytically pure, 99%) thoroughly in a molar ratio of 1:0.1 (LiBO.sub.2:SrF.sub.2), placed into a platinum crucible, heated to 790 C. and kept at this temperature for 15 hours, to generate a mixed solution containing the lithium metaborate and flux.

(149) Preparation of the lithium metaborate seed crystal: a platinum wire fixed to a seed rod was placed into the mixed solution, and then the temperature was slowly reduced at a rate of 3 C./h until crystal formed on the platinum wire. Then the rod was rotated at a rate of 2 r/min and the temperature was slowly reduced at a rate of 1 C./d. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was decreased to room temperature at a rate of 30 C./h. As a result, lithium metaborate seed crystal was obtained.

(150) The crucible containing the obtained mixed solution was placed into a crystal growth furnace, the obtained seed crystal was fixed to the seed rod, and the temperature was reduced to 740 C. Thereafter, the seed crystal was placed into the hearth from the top of the furnace, and preheated for 10 minutes above the surface of the mixed solution. Then the seed crystal was moved down to contact with the surface of the mixed solution for remelting. The temperature was held for 8 minutes before decreased rapidly to 733 C.

(151) Then the temperature was reduced slowly at a rate of 0.5 C./d and the seed rod was rotated at a rate of 2 r/min, so as to ensure superior growth of the crystal. At the same time, the crystal was lifted up at a rate of 0.2 mm/h. As growing into a desired size, the crystal was lifted out of the mixed solution and the temperature was reduced to room temperature at a rate of 20 C./h. Then the crystal, i.e., metaborate crystal in a size of 14129 mm.sup.3 was obtained and collected from the hearth.

Example 27. Growth of Lithium Metaborate Crystal by Bridgman-Stockbarger Method

(152) The seed crystal obtained from anyone of Examples 1-26 was placed into the seed groove at the bottom of a crucible. Analytically pure (99%) LiBO.sub.2 and B.sub.2O.sub.3 were mixed in a molar ratio of 1:1.02 (Li:B) and ground thoroughly: then placed into the crucible. The crucible was covered by a lid and placed into a furnace with temperature gradient. The temperature was increased to 870 C. and kept for 20 hours. Then the crucible was moved downwards at a rate of 0.5 mm/h. When crystallization was completed, the temperature was reduced to room temperature at a rate of 50 C./h. As a result, lithium metaborate crystal in a size of 342928 mm.sup.3 was obtained.

Example 28. Growth of Lithium Metaborate Crystal by Bridgman-Stockbarger Method

(153) The seed crystal obtained from anyone of Examples 1-26 was placed into the seed groove at the bottom of a crucible. Li.sub.2CO.sub.3 and B.sub.2O.sub.3 were mixed in a molar ratio of 1:1.06 (Li:B) and ground thoroughly. The mixture was sintered before added into the crucible. Thereafter the crucible was covered by a lid and placed into a furnace with temperature gradient. The temperature was increased to 865 C. and held for 10 hours. Then the crucible was moved downwards at a rate of 1 mm/h. When crystallization was completed, the temperature was reduced to room temperature at a rate of 10 C./h. As a result, lithium metaborate crystal in a size of 373134 mm.sup.3 was obtained.

Example 29. Growth of Lithium Metaborate Crystal by Bridgman-Stockbarger Method

(154) The seed crystal obtained from anyone of Examples 1-26 was placed into the seed groove at the bottom of a crucible. Then analytically pure (99%) LiBO.sub.2 was added into the crucible. The crucible was covered by a lid and placed into a furnace with temperature gradient. The temperature was increased to 880 C. and held for 1 hour. Then the crucible was moved downwards at a rate of 2 mm/h. When crystallization was completed, the temperature was reduced to room temperature at a rate of 30 C./h. As a result, lithium metaborate crystal in a size of 342928 mm.sup.3 was obtained.

Example 30. Growth of Lithium Metaborate Crystal by Bridgman-Stockbarger Method

(155) The seed crystal obtained from anyone of Examples 1-26 was placed into the seed groove at the bottom of a crucible. LiNO.sub.3 and B.sub.2O.sub.3 were mixed in a molar ratio of 1:1.1 (Li:B) and ground thoroughly. The mixture was sintered before added into the crucible. Thereafter the crucible was, covered by a lid and placed into a furnace with temperature gradient. The temperature was increased to 850 C. and held for 5 hours. Then the crucible was moved downwards at a rate of 0.1 mm/h. When crystallization was completed, the temperature was reduced to room temperature at a rate of 20 C./h. As a result, lithium metaborate crystal in a size of 352831 mm.sup.3 was obtained.

Example 31

(156) The LiBO.sub.2 crystal obtained from anyone of Examples 1-30 was used to manufacture a wedge-shaped birefringent crystal polarization splitter (as shown in FIG. 4). As a wedge-shaped birefringent crystal, it optic axis was in the direction shown in FIG. 4. When irradiating upon and through the crystal, a natural light beam splited into two rays of linearly polarized light. The larger the birefringence was, the farther the two rays were separated apart, which benefits beam separation.

Example 32

(157) The LiBO.sub.2 crystal obtained from anyone of Examples 1-30 was used to manufacture a beam shifter. Birefringent crystal was processed to have an angle between its optic axial plane and edge (as shown in FIG. 5a). When irradiating upon the crystal vertically, a natural light beam splited into two rays of linearly polarized light vibrating in directions vertical to each other (as shown in FIG. 5b), namely, light o and light e, respectively. The larger the birefringence was, the farther the two rays were separated apart, which benefits beam separation.

Example 33

(158) The LiBO.sub.2 crystal obtained from anyone of Examples 1-30 was used to manufacture an opto-isolator. An opto-isolator was constructed by placing a Faraday rotator, whose incident beam polarization plane had been rotated 45 between two birefringent crystal deflectors arranged at a cross angle of 45. This opto-isolator only allowed the forward transmitting incident light to pass through the system, but interrupted the backward transmitting light. FIG. 6a shows that an incident light passed through the system, whereas FIG. 6b shows that the reflecting light was interrupted.