A free-standing substrate of a polycrystalline nitride of a group 13 element is composed of a plurality of monocrystalline particles having a particular crystal orientations in approximately a normal direction. The free-standing substrate has a top surface and a bottom surface. The polycrystalline nitride of the group 13 element is gallium nitride, aluminum nitride, indium nitride or a mixed crystal thereof and contains zinc at a concentration of 110.sup.17 atoms/cm.sup.3 or more and 110.sup.20 atoms/cm.sup.3 or less.

A crystal growth apparatus includes: a raw material supplying part that mixes raw materials including a group III element metal and an alkali metal; a growing part disposed at a stage under the raw material supplying part, the growing part having a seed substrate; a tilting mechanism that tilts the raw material supplying part and the growing part; a heater that heats the raw material supplying part and the growing part; a control part that controls an operation of the tilting mechanism; and a supply port that supplies a nitrogen element-containing substance to the growing part, wherein the raw material supplying part having an opening facing to the growing part, the opening being disposed at a bottom portion and one edge portion of the raw material supplying part, and the control part controls the tilting mechanism so as to tilt the raw material supplying part toward the other edge portion on the side opposite to the one edge portion so as to prevent the raw materials from entering the opening when the raw materials are mixed, and the control part controls the tilting mechanism so as to tilt the raw material supplying part toward the one edge portion so that the raw materials drop through the opening to the growing part when the mixing of the raw materials is completed.

A crystal growth apparatus includes: a raw material supplying part that mixes raw materials including a group III element metal and an alkali metal; a growing part disposed at a stage under the raw material supplying part, the growing part having a seed substrate; a tilting mechanism that tilts the raw material supplying part and the growing part; a heater that heats the raw material supplying part and the growing part; a control part that controls an operation of the tilting mechanism; and a supply port that supplies a nitrogen element-containing substance to the growing part, wherein the raw material supplying part having an opening facing to the growing part, the opening being disposed at a bottom portion and one edge portion of the raw material supplying part, and the control part controls the tilting mechanism so as to tilt the raw material supplying part toward the other edge portion on the side opposite to the one edge portion so as to prevent the raw materials from entering the opening when the raw materials are mixed, and the control part controls the tilting mechanism so as to tilt the raw material supplying part toward the one edge portion so that the raw materials drop through the opening to the growing part when the mixing of the raw materials is completed.

A crystal growth apparatus includes a pressure-resistant vessel; a plurality of support tables arranged inside the pressure-resistant vessel; inner vessels each placed over the support tables, respectively; growth vessels contained the inner vessels, respectively; a heating means for heating the growth vessels; and a central rotating shaft connected to the support tables. The central rotating shaft is distant from central axes of the inner vessels, respectively. A seed crystal, a raw material of the Group 13 element and a flux are charged in each of the growth vessels, and the growth vessels are heated to form a melt and a nitrogen-containing gas is supplied to the melt to grow a crystal of a nitride of said Group 13 element while the central rotating shaft is rotated.

A crystal growth apparatus includes a pressure-resistant vessel; a plurality of support tables arranged inside the pressure-resistant vessel; inner vessels each placed over the support tables, respectively; growth vessels contained the inner vessels, respectively; a heating means for heating the growth vessels; and a central rotating shaft connected to the support tables. The central rotating shaft is distant from central axes of the inner vessels, respectively. A seed crystal, a raw material of the Group 13 element and a flux are charged in each of the growth vessels, and the growth vessels are heated to form a melt and a nitrogen-containing gas is supplied to the melt to grow a crystal of a nitride of said Group 13 element while the central rotating shaft is rotated.

A method for producing a gallium nitride crystal includes growing a gallium nitride crystal 5 by dissolving nitrogen in a mixed melt including gallium and sodium, and collecting the gallium 55 separated from an alloy 51 including the gallium and the sodium by reacting the alloy 51 and a liquid 52 that ionizes the sodium and separating sodium ions and the gallium 55 from the alloy.

A method for producing a gallium nitride crystal includes growing a gallium nitride crystal 5 by dissolving nitrogen in a mixed melt including gallium and sodium, and collecting the gallium 55 separated from an alloy 51 including the gallium and the sodium by reacting the alloy 51 and a liquid 52 that ionizes the sodium and separating sodium ions and the gallium 55 from the alloy.

The present invention provides a method for preparing graphene by using a molten inorganic salt reaction bed. The method includes the following steps: using phthalocyanine substance as a reaction raw material, well-mixing an inorganic salt with the phthalocyanine substance in the inorganic salt reaction bed, performing pyrolysis by using a temperature programmed method in an atmosphere furnace under a protective gas, and separating out a highly planar-oriented graphene material. By adopting the method, a graphene material can be obtained by pyrolysis in a non-hydrogen environment. The method is simple, the process is environmentally friendly, industrial production can be achieved, and the obtained graphene is highly planar-oriented.

The present invention provides a method for preparing graphene by using a molten inorganic salt reaction bed. The method includes the following steps: using phthalocyanine substance as a reaction raw material, well-mixing an inorganic salt with the phthalocyanine substance in the inorganic salt reaction bed, performing pyrolysis by using a temperature programmed method in an atmosphere furnace under a protective gas, and separating out a highly planar-oriented graphene material. By adopting the method, a graphene material can be obtained by pyrolysis in a non-hydrogen environment. The method is simple, the process is environmentally friendly, industrial production can be achieved, and the obtained graphene is highly planar-oriented.

A nonlinear optical crystal of barium cesium borate, a preparation method and use thereof are provided. The nonlinear optical crystal has a chemical formula of CsBa.sub.3B.sub.11O.sub.20 and a molecular weight of 983.84. The nonlinear optical crystal belongs to an orthorhombic crystal system; a space group of the nonlinear optical crystal is Cmc2.sub.1; lattice parameters of the nonlinear optical crystal are a=19.011(7) ?, b=10.837(4) ?, c=8.578(3) ?, Z=4, V=1767.4(11) ?.sup.3; and a Mohs hardness of the nonlinear optical crystal is 4-5. The nonlinear optical crystal is grown by a flux method. The nonlinear optical crystal of the barium cesium borate obtained is used for a manufacture of non-linear optical devices. The nonlinear optical crystal has a large size of centimeter-scale at least and is prepared by fast, simple and low-cost operations. The nonlinear optical crystal prepared has a large size, a wide light transmission band and good mechanical properties.