An oxychloride infrared nonlinear optical crystal and the preparation method and use thereof, the optical crystal has a general chemical formula of Pb.sub.2+xOCl.sub.2+2x, therein 0<x<0.139 or 0.141<x<0.159 or 0.161<x0.6. The crystal is non-centrosymmetric, belongs to orthonormal system with space group of Fmm2, cell parameter is a=35.4963(14)0.05 , b=5.8320(2)0.05 , c=16.0912(6)0.05 . The crystal is prepared by high temperature melt method or flux method. The crystal has a strong second harmonic generation efficiency of 4 times that of KDP (KH.sub.2PO.sub.4) tested by Kurtz method, it is phase machable, transparent in the range of 0.34-7 m. The laser damage threshold is 10 times that of the current commercial infrared nonlinear optical crystal AgGaS.sub.2. No crystalline water exists in lead oxychloride, and it is stable in the air and has good thermal stability.

An oxychloride infrared nonlinear optical crystal and the preparation method and use thereof, the optical crystal has a general chemical formula of Pb.sub.2+xOCl.sub.2+2x, therein 0<x<0.139 or 0.141<x<0.159 or 0.161<x0.6. The crystal is non-centrosymmetric, belongs to orthonormal system with space group of Fmm2, cell parameter is a=35.4963(14)0.05 , b=5.8320(2)0.05 , c=16.0912(6)0.05 . The crystal is prepared by high temperature melt method or flux method. The crystal has a strong second harmonic generation efficiency of 4 times that of KDP (KH.sub.2PO.sub.4) tested by Kurtz method, it is phase machable, transparent in the range of 0.34-7 m. The laser damage threshold is 10 times that of the current commercial infrared nonlinear optical crystal AgGaS.sub.2. No crystalline water exists in lead oxychloride, and it is stable in the air and has good thermal stability.

A method for producing a group 13 nitride single crystal includes dissolving and crystal growing. The dissolving includes dissolving nitrogen in a mixed melt in a reaction vessel that contains the mixed melt, a seed crystal, and a surrounding member. The mixed melt contains an alkali metal and a group 13 metal. The seed crystal is a seed crystal that is placed in the mixed melt and includes a group 13 nitride crystal in which a principal face is a c-plane. The surrounding member is arranged so as to surround the entire area of a side face of the seed crystal. The crystal growing includes growing a group 13 nitride crystal on the seed crystal.

A method for producing a group 13 nitride single crystal includes dissolving and crystal growing. The dissolving includes dissolving nitrogen in a mixed melt in a reaction vessel that contains the mixed melt, a seed crystal, and a surrounding member. The mixed melt contains an alkali metal and a group 13 metal. The seed crystal is a seed crystal that is placed in the mixed melt and includes a group 13 nitride crystal in which a principal face is a c-plane. The surrounding member is arranged so as to surround the entire area of a side face of the seed crystal. The crystal growing includes growing a group 13 nitride crystal on the seed crystal.

Provided is a method for producing a SiC single crystal wherein generation of polycrystals can be inhibited even if the temperature of the SiC solution is changed after seed touching. This is achieved by a method for producing a SiC single crystal wherein a SiC seed crystal substrate held on a seed crystal holding shaft is contacted with a SiC solution having a temperature gradient in which the temperature decreases from the interior toward the surface, to grow a SiC single crystal, comprising the steps of: (A) bringing the temperature of the solution to a first temperature, (B) contacting the substrate held on the holding shaft with the solution, (C) bringing the temperature of the solution to a second temperature after the contacting the substrate with the solution, and (D) moving the substrate held on the holding shaft in the vertical direction according to the change in liquid surface height of the solution when the temperature of the solution is brought from the first temperature to the second temperature.

Provided is a method for producing a SiC single crystal wherein generation of polycrystals can be inhibited even if the temperature of the SiC solution is changed after seed touching. This is achieved by a method for producing a SiC single crystal wherein a SiC seed crystal substrate held on a seed crystal holding shaft is contacted with a SiC solution having a temperature gradient in which the temperature decreases from the interior toward the surface, to grow a SiC single crystal, comprising the steps of: (A) bringing the temperature of the solution to a first temperature, (B) contacting the substrate held on the holding shaft with the solution, (C) bringing the temperature of the solution to a second temperature after the contacting the substrate with the solution, and (D) moving the substrate held on the holding shaft in the vertical direction according to the change in liquid surface height of the solution when the temperature of the solution is brought from the first temperature to the second temperature.

Disclosed is a nonlinear optical material (NLO) for use in deep-UV applications, and methods of fabrication thereof. The NLO is fabricated from a plurality of components according to the formula A.sub.qB.sub.yC.sub.z and a crystallographic non-centrosymmetric (NCS) structure. The NLO material may be fabricated as a polycrystalline or a single crystal material. In an embodiment, the material may be according to a formula Ba.sub.3ZnB.sub.5PO.sub.14.

In the present invention, a crucible formed of SiC as a main component is used as a container for a SiC solution. A metal element M (M is at least one metal element selected from at least one of a first group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Lu, a second group consisting of Ti, V, Cr, Mn, Fe, Co, Ni and Cu and a third group consisting of Al, Ga, Ge, Sn, Pb and Zn) is added to the SiC solution and the crucible is heated to elute Si and C, which are derived from a main component SiC of the crucible, from a high-temperature surface region of the crucible in contact with the SiC solution, into the SiC solution. In this way, precipitation of a SiC polycrystal on a surface of the crucible in contact with the SiC solution is suppressed.

In the present invention, a crucible formed of SiC as a main component is used as a container for a SiC solution. A metal element M (M is at least one metal element selected from at least one of a first group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho and Lu, a second group consisting of Ti, V, Cr, Mn, Fe, Co, Ni and Cu and a third group consisting of Al, Ga, Ge, Sn, Pb and Zn) is added to the SiC solution and the crucible is heated to elute Si and C, which are derived from a main component SiC of the crucible, from a high-temperature surface region of the crucible in contact with the SiC solution, into the SiC solution. In this way, precipitation of a SiC polycrystal on a surface of the crucible in contact with the SiC solution is suppressed.

A method for producing a SiC substrate with an epitaxial layer, which can prevent inventory of wafers from unduly increasing and wasteful production, is provided. This is achieved by a method for producing a SiC substrate with an epitaxial layer one at a time, the method comprising growing an epitaxial layer and growing a SiC substrate on a seed crystal substrate, and the method further comprising removing the obtained SiC substrate with the epitaxial layer from the seed crystal substrate.