Preparation method and application of sodium barium fluoroborate birefringent crystal

Abstract

A preparation method and application of a Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F birefringent crystal, the crystal having a chemical formula of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F, and belonging to a hexagonal crystal system, the space group being P6.sub.3/m, and the lattice parameters comprising a=7.3490(6) , c=12.6340(2) , V=590.93(12) .sup.3, Z=2; the crystal is used for an infrared/deep ultraviolet waveband, and is an uniaxial negative crystal, n.sub.e<n.sub.o, the transmission range being 175-3,350 nm, the birefringence of 0.090 (3,350 nm)-0.240 (175 nm), and the crystal being grown by employing a melting method or a flux method; the crystal prepared via the method has a short growth cycle, high crystal quality and large crystal size, is easy to grow, cut, polish and store, is stable in the air, and difficult to deliquesce, and can be used for preparation of various polarization beam polarization beam splitter prism and infrared/deep ultraviolet waveband optical communication elements.

Claims

1. A method for preparing sodium barium fluoborate birefringent crystal, characterized in that said crystal is grown by melt method including the top seeding method, the Kyropoulos method or the Czochralski method, according to the specific steps as follows: a. mixing and grinding a sodium-containing compound, barium-containing compound, boron-containing compound and fluorine-containing compound at a molar ratio of sodium:barium:boron:fluorine=3:2:6:1 to provide a mixture, charging the mixture into a platinum crucible, heating the mixture to a temperature higher than 820 C. to obtain a high-temperature mixed melt, and maintaining this temperature for 1-100 hours; b. growing the crystal on the surface of or inside the mixed melt: decreasing the temperature of the mixed melt of Step (a) to 820-825 C., fixing a seed crystal to a seed crystal rod and preheating the seed crystal above the mixed melt for 1-100 minutes, then decreasing the temperature of the mixed melt to 810-820 C., descending the seed crystal onto the surface of or into the mixed melt while rotating the seed crystal or the crucible at a rotation speed of greater than 0 to 100 r/min, increasing or decreasing the temperature of the mixed melt at a rate of greater than 0 to 5 C./d, and meanwhile drawing the crystal at a drawing speed of greater than 0 to 15 mm/h; c. when growing the crystal to a desired size, increasing the drawing speed so as to draw the crystal out of the surface of the mixed melt, decreasing the temperature to room temperature at a rate of 1-100 C./h, and then taking the crystal out of the crucible to obtain a Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F birefringent crystal.

2. The method for preparing the sodium barium fluoborate birefringent crystal according to claim 1, characterized in that, in Step (a), said sodium-containing compound is 99.9% pure sodium oxide, sodium hydroxide, sodium carbonate, sodium nitrate or sodium metaborate; said barium-containing compound is 99.9% pure barium oxide, barium hydroxide, barium fluoride, barium carbonate or barium nitrate; said boron-containing compound is 99.9% pure boric acid or boron oxide; and said fluorine-containing compound is 99.9% pure sodium fluoride or barium fluoride.

3. The method for preparing the sodium barium fluoborate birefringent crystal according to claim 1, characterized in that the sodium barium fluoborate birefringent crystal obtained by said method is a negative uniaxial crystal, n.sub.e<n.sub.o, having a birefringence index of 0.090-0.240 and a transmission range of 175-3,350 nm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a structural representation of the Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F birefringent crystal.

(2) FIG. 2 shows an X-ray diffraction pattern of the powder of the Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F birefringent crystal.

(3) FIG. 3 shows a schematic illustration of the large-size transparent as-grown Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F birefringent crystal in the invention.

(4) FIG. 4 shows a schematic illustration of a birefringent crystal wedge for polarization beam splitter made from the as-grown crystal according to the method of the invention.

(5) FIGS. 5A and 5B are schematic illustrations of optoisolators made from the as-grown crystal according to the method of the invention.

(6) FIGS. 6A and 6B show a schematic illustration of a beam shifter made from the as-grown crystal according to the method of the invention;

(7) wherein 1 is incident light, 2 is o-ray, 3 is e-ray, 4 is an optical axis, and 5 is the Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal, 6 is the transmission direction of the light, and 7 is an optic-axial plane.

EXAMPLES

Example 1

Growing the Na3Ba2(B3O6)2F birefringent crystal by the top seeding method from the stoichiometric melt

(8) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaCO.sub.3+6H.sub.3BO.sub.3.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O
wherein the raw materials used (analytically pure) were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaCO.sub.3 236.832 g and H.sub.3BO.sub.3 222.616 g (the molar ratio of Na:Ba:B:F was 3:2:6:1), and the method comprises the following steps:

(9) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to a temperature of 830 C. to obtain a mixed melt, followed by maintaining this temperature for 48 hours;

(10) The crystal was grown on the surface of the mixed melt: the temperature of the mixed melt was firstly decreased to 821 C., a seed crystal was then fixed to a seed crystal rod and preheated at a distance of 0-10 mm above the melt for 30 minutes; then the temperature of the mixed melt was decreased to 819-820 C. and the seed crystal was descended onto the surface of the mixed melt while rotating the seed crystal at a rate of 15 r/min, decreasing the temperature of the mixed melt at a rate of 0-0.3 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(11) After 3 days when the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5-25 C./h, and then the crystal was taken out of the furnace slowly to obtain a transparent 503112 mm.sup.3 sodium barium fluoborate birefringent crystal. The obtained crystal was subjected to a light transmission measurement and the results showed that it had a transmission range of 175-3,350 nm and a birefringence index of 0.090-0.240.

(12) The crystal grown according to this method had a significantly shortened growth cycle and much better quality, without wrappages or cracks.

Example 2

Growing the Na3Ba2(B3O6)2F Birefringent Crystal by the Kyropoulos Method from the Stoichiometric Melt

(13) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaCO.sub.3+6H.sub.3BO.sub.3.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O
wherein the raw materials used (analytically pure) were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaCO.sub.3 236.832 g and H.sub.3BO.sub.3 222.616 g (the molar ratio of Na:Ba:B:F was 3:2:6:1), and the method comprises the following steps:

(14) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to a temperature of 830 C. to obtain a mixed melt, followed by maintaining this temperature for 48 hours;

(15) The crystal was grown in the mixed melt: the temperature of the mixed melt was firstly decreased to 821 C., a seed crystal was then fixed to a seed crystal rod and preheated at a distance of 0-10 mm above the melt for 30 minutes; then the temperature of the mixed melt was decreased to 819-820 C. and the seed crystal was descended into the mixed melt while rotating the seed crystal at a rate of 10 r/min, decreasing the temperature of the mixed melt at a rate of 0-0.3 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(16) After 2.5 days when the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5-25 C./h, and then the crystal was taken out of the furnace slowly to obtain a transparent 403513 mm.sup.3 sodium barium fluoborate birefringent crystal. The obtained crystal was subjected to a light transmission measurement and the results showed that it had a transmission range of 175-3,350 nm and a birefringence index of 0.090-0.240.

(17) The crystal grown according to this method had a significantly shortened growth cycle and much better quality, without wrappages or cracks, and in the meantime the obtained crystal had a further increase in thickness, which facilitate further process and application.

Example 3

Growing the Na3Ba2(B3O6)2F Birefringent Crystal by the Czochralski Method from the Stoichiometric Melt

(18) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaCO.sub.3+6H.sub.3BO.sub.3.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O
wherein the raw materials used (analytically pure) were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaCO.sub.3 236.832 g and H.sub.3BO.sub.3 222.616 g (the molar ratio of Na:Ba:B:F was 3:2:6:1), the method comprises the following steps:

(19) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to a temperature of 830 C. to obtain a mixed melt, followed by maintaining this temperature for 48 hours;

(20) The temperature of the mixed melt was decreased to 821 C., a seed crystal was then fixed to a seed crystal rod and preheated at a distance of 0-10 mm above the melt for 30 minutes; then the temperature of the mixed melt was decreased to 819-820 C. and the seed crystal was descended onto the surface of the mixed melt while rotating the seed crystal at a rate of 10 r/min and meanwhile drawing the crystal up at a speed of 0-1 mm/h; when the crystal started to grow, the process of shouldering and necking was performed to further optimize the quality of the seed crystal; the drawing speed was kept at 2 mm/h and the mixed melt was cooled at a rate of 0-0.3 C./d, allowing the crystal to grow continuously at a constant diameter.

(21) After 1.5 days when the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5-25 C./h, and then the crystal was taken out of the furnace slowly to obtain a transparent 424232 mm.sup.3 sodium barium fluoborate birefringent crystal. The obtained crystal subjected to a light transmission measurement and the results showed that it had a transmission range of 175-3,350 nm and a birefringence index of 0.090-0.240.

(22) The crystal grown according to this method had a further shortened growth cycle and a further increased thickness, and the crystal was transparent, without wrappages or cracks. This method further facilitated fast growth of large and thick optical-quality monocyrstal.

Example 4

Growing Na3Ba2(B3O6)2F by the Flux Method

(23) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaO+6H.sub.3BO.sub.3+0.6BaF.sub.2.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HF
wherein the raw materials used (analytically pure) were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaO 184.008 g, H.sub.3BO.sub.3 222.616 g and BaF.sub.2 63.115 g (the molar ratio of Na:Ba:B:F:BaF.sub.2 was 3:2:6:1:0.6, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to BaF.sub.2 was 1:0.6), and the method comprised the following steps:

(24) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 30 hours;

(25) The mixed melt comprising the flux was cooled to 790 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 15 r/min, slowly cooling the mixed melt at a rate of 0.2 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(26) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 30236 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 5

Growing Na3Ba2(B3O6)2F by the Flux Method

(27) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2Ba(OH).sub.2+6H.sub.3BO.sub.3+0.4B.sub.2O.sub.3.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, Ba(OH).sub.2 205.620 g, H.sub.3BO.sub.3 222.616 g and B.sub.2O.sub.3 16.708 g (the molar ratio of Na:Ba:B:F:B.sub.2O.sub.3 was 3:2:6:1:0.4, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to B.sub.2O.sub.3 was 1:0.4), and the method comprised the following steps:

(28) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 25 hours;

(29) The mixed melt comprising the flux was cooled to 787 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace onto the surface of the mixed melt, while rotating the seed crystal rod at a rate of 35 r/min, slowly cooling the mixed melt at a rate of 0.1 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(30) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 8 C./h, and then the crystal was taken out of the furnace slowly to obtain a 23186 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 6

Growing Na3Ba2(B3O6)2F by the Flux Method

(31) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaH.sub.2Ba.sub.2CO.sub.330 2BaCl.sub.2+6H.sub.3BO.sub.3+NaCl.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HCl
wherein the raw materials used (analytically pure) were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaCl.sub.2 249.984 g, H.sub.3BO.sub.3 222.616 g and NaCl 35.064 g (the molar ratio of Na:Ba:BT:NaCl is 3:2:6:1:1, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to NaCl was 1:1), and the method comprised the following steps:

(32) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 30 hours;

(33) The mixed melt comprising the flux was cooled to 782 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 30 r/min, cooling the mixed melt slowly at a rate of 0.5 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h.

(34) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 16156 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 7

Growing Na3Ba2(B3O6)2F by the Flux Method

(35) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaBr.sub.2+6H.sub.3BO.sub.3+2NaBO.sub.2.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HBr
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaBr.sub.2 356.028 g, H.sub.3BO.sub.3 222.616 g and NaBO.sub.2 78.960 g (the molar ratio of Na:Ba:B:F:NaBO.sub.2 was 3:2:6:1:2, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to NaBO.sub.2 was 1:2), and the method comprised the following steps:

(36) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 24 hours;

(37) The mixed melt liquid comprising the flux was cooled to 753 C., a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 35 r/min, slowly cooling the mixed melt at a rate of 0.5 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(38) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 27168 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 8

Growing the Na3Ba2(B3O6)2F by the Flux Method

(39) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaBr.sub.2+6H.sub.3BO.sub.3+2.5NaNO.sub.3.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2HBr+NO.sub.2
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaBr.sub.2 356.028 g, H.sub.3BO.sub.3 222.616 g and NaNO.sub.3 127.485 g (the molar ratio of Na:Ba:B:F:NaNO.sub.3 was 3:2:6:1:2.5, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to NaNO.sub.3 was 1:2.5), and the method comprised the following steps:

(40) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 24 hours;

(41) The mixed melt comprising the flux was cooled to 790 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 20 r/min, slowly cooling the mixed melt at a rate of 0.5 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h.

(42) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 32249 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 9

Growing the NBBF Birefringent Crystal with Flux

(43) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaBr.sub.2+6H.sub.3BO.sub.3+3NaBr.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HBr
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaBr.sub.2 356.028 g, H.sub.3BO.sub.3 222.616 g and NaBr 185.202 g (the molar ratio of Na:Ba:B:F:NaBr is 3:2:6:1:3, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to NaBr was 1:3), and the method comprised the following steps:

(44) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 24 hours;

(45) The mixed melt comprising the flux was cooled to 747 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace onto the surface of the mixed melt, while rotating the seed crystal rod at a rate of 15 r/min and slowly cooling the mixed melt at a rate of 0.2 C./d and meanwhile drawing the crystal up at a speed of 0-15 mm/h.

(46) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 352310 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 10

Growing Na3Ba2(B3O6)2F by the Flux Method

(47) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaBr.sub.2+6H.sub.3BO.sub.3+2NaBr.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HBr
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaBr.sub.2 356.028 g, H.sub.3BO.sub.3 222.616 mg and NaBr 123.468 g (the molar ratio of Na:Ba:B:F:NaBr was 3:2:6:1:2, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to NaBr was 1:2), and the method comprises the following steps:

(48) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 30 hours;

(49) The mixed melt comprising the flux was cooled to 772 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 20 r/min, slowly cooling the mixed melt at a rate of 0.4 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(50) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 23156 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 11

Growing Na3Ba2(B3O6)2F by the Flux Method

(51) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaBr.sub.2+6H.sub.3BO.sub.3+4NaBO.sub.2.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HBr
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaBr.sub.2 356.028 g, H.sub.3BO.sub.3 222.616 g and NaBO.sub.2 157.920 g (the molar ratio of Na:Ba:B:F:NaBO.sub.2 was 3:2:6:1:4, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to NaBO.sub.2 was 1:4), and the method comprised the following steps:

(52) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 min100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 24 hours;

(53) The mixed melt comprising the flux was cooled to 724 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 45 r/min, slowly cooling the mixed melt at a rate of 0.3 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(54) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 322412 mm.sup.3 sodium barium fluoborate birefringent crystal.

Example 12

Grow Na3Ba2(B3O6)2F by the Flux Method

(55) The Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal was prepared according to the following reaction equation:
NaF+Na.sub.2CO.sub.3+2BaO+6H.sub.3BO.sub.3+BaF.sub.2.fwdarw.Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F+CO.sub.2+H.sub.2O+HF
wherein the raw materials (analytically pure) used were: NaF 25.194 g, Na.sub.2CO.sub.3 63.597 g, BaO 184.008 g, H.sub.3BO.sub.3 222.616 g and BaF.sub.2 105.192 g (the molar ratio of Na:Ba:B:F:BaF.sub.2 was 3:2:6:1:1, that is, the molar ratio of Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F to BaF.sub.2 was 1:1), and the method comprised the following steps:

(56) The weighed raw materials were mixed and grounded in a mortar, and then charged into a 100 mm100 mm platinum crucible, the obtained mixture was heated to 820 C. to obtain a mixed melt, followed by maintaining this temperature for 30 hours;

(57) The mixed melt comprising the flux was cooled to 772 C.; a seed crystal was fixed to a seed crystal rod and then descended from the top of a furnace into the mixed melt, while rotating the seed crystal rod at a rate of 10 r/min, slowly cooling the mixed melt at a rate of 0.3 C./d, and meanwhile drawing the crystal up at a speed of 0-15 mm/h;

(58) After the monocrystal was grown up to a desired size, the drawing speed was increased so as to draw the crystal out of the melt liquid surface; the temperature of the furnace was decreased to room temperature at a rate of 5 C./h, and then the crystal was taken out of the furnace slowly to obtain a 432813 mm.sup.3 sodium barium fluoborate birefringent crystal.

(59) FIG. 1 shows a structural representation of the Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F sodium barium fluoborate birefringent crystal, wherein the basic unit of the crystal structure is B.sub.3O.sub.6 which constitutes parallel B.sub.3O.sub.6 layers, and Na, Ba and F are intercalated between the layers, so that a three-dimensional net structure is formed.

(60) FIG. 2 shows an X-ray diffraction pattern of the powder of the Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F sodium barium fluoborate birefringent crystal. As shown in the figure, the diffraction peaks are sharp and symmetrical, and high in intensity.

(61) FIG. 3 shows the schematic illustration of the large-size transparent Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F birefringent crystal, which is transparent and of high quality, without cracks.

Example 13

(62) Any Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal obtained in Examples 1-3 was used for preparing a birefringent crystal wedge for polarization beam splitter (as shown in FIG. 4), wherein a wedge birefringent crystal was oriented so that its optical axis was as shown in FIG. 4; after incident upon the crystal, a natural light beam 1 would be split into two linearly polarized light beams (linearly polarized light 2 and linearly polarized light 3), the greater the birefringence index, the farther the two light beams may be separated. in FIG. 4 is the angulus parietalis of the wedge birefringent crystal polarization beam splitter.

Example 14

(63) Any Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal obtained in Examples 1-3 was used for preparing a optoisolator, wherein a Faraday optical rotator with an incident light beam polarization plane rotated by 45 was configured between a pair of birefringent crystal deflectors (1 and 3) which were arranged crosswise at an angle of 45, and therefore an optoisolator was constituted. The optoisolator only allowed forward-propagating light beams to pass through the system but blocked the back-propagating light beams. FIG. 5A shows that the incident light can get through, while FIG. 5B shows that the reflected light is blocked.

Example 15

(64) Any Na.sub.3Ba.sub.2(B.sub.3O.sub.6).sub.2F crystal obtained in Examples 1-3 was used for preparing a beam shifter. A birefringent crystal was processed so that its optic-axial plane formed an Angle with the arris (as shown in FIG. 6A). Upon perpendicular incidence, the natural light may be split into two linearly polarized light beams having perpendicular vibration directions (as shown in FIG. 6B), that is, o-ray and e-ray, the greater the birefringence index, the farther the two light beams may be separated, which facilitates beam splitting.