Abstract: Provided is an apparatus capable of producing a fluoride crystal in a very short period of time, and a method suitable for producing a fluoride crystal using the apparatus. The apparatus comprises a chamber, a window material, and the like, and is modified such that it can evacuate air from the chamber to provide a high degree vacuum there. The apparatus further includes a crucible, which has a perforation at its bottom. The capillary portion of the perforation is adjusted to facilitate the contact of a seed crystal with a melt. By using the apparatus it is possible to stably produce high quality single crystals of fluorides in a short period of time.

Abstract: A material for high-temperature region piezoelectric device that can be used at a high temperature zone exceeding 400 DEG C, having a resistivity whose temperature dependence is slight. The material is characterized by having a composition selected from the group consisting of RE3Ga5?xAlxSiO14 (wherein RE represents a rare earth, and 0<X<5), RE3Ta0.5Ga5.5?xAlxO14 (wherein RE represents a rare earth, and 0<X<5.5) and RE3Nb0.5Ga5.5?xAlxO14 (wherein RE represents a rare earth, and 0<x<5.5) and by exhibiting a 100 to 600° C. resistivity change of ?104. The process for producing the same is characterized by growing a single crystal from a solution in an atmosphere of inert gas containing an oxidative gas and thereafter cooling the single crystal in an inert gas whose oxidative gas molar fraction (z) is lower than in the above growing step.

Abstract: To produce a zinc oxide single crystal having a sufficiently low lithium concentration and a high crystallinity. A zinc oxide crystal is grown by hydrothermal synthesis method using a solution having a lithium concentration of 1 ppm or less (weight basis), while suppressing a fluctuation range of crystal growth temperature within 5° C. or at a temperature within the range of 300 to 370° C.

Abstract: It is an object of the present invention to provide a self-coated single crystal that without any special step conducted after crystal growth, has its circumference coated with a layer of different properties. A self-coated single crystal according to the present invention is characterized in that in operations comprising melting crystal materials for a core and a clad in a single crucible and carrying out growth of a single crystal through a pulling up method or a pulling down method, a grown single crystal in an as-growth condition has its circumference self-coated with a clad whose refractive index is lower than that of the core.

Abstract: It is aimed at providing a fluoride crystal growing method capable of controlling a shape of the crystal by a micro-pulling-down method. Fluoride crystals in shapes depending on purposes, respectively, can be grown by adopting carbon, platinum, and iridium as crucible materials adaptable to fluorides, respectively, and by designing shapes of the crucibles taking account of wettabilities of the materials with the fluorides, respectively.

Abstract: A material for high-temperature region piezoelectric device that can be used at a high temperature zone exceeding 400 DEG C., having a resistivity whose temperature dependence is slight. The material is characterized by having a composition selected from the group consisting of RE3Ga5?xAlxSiO14 (wherein RE represents a rare earth, and 0<x<5), RE3Ta0.5Ga5.5?xAlxO14 (wherein RE represents a rare earth, and 0<X<5.5) and RE3Nb0.5Ga5.5?xAlxO14 (wherein RE represents a rare earth, and 0<x<5.5) and by exhibiting a 100 to 600° C. resistivity change of ?104. The process for producing the same is characterized by growing a single crystal from a solution in an atmosphere of inert gas containing an oxidative gas and thereafter cooling the single crystal in an inert gas whose oxidative gas molar fraction (z) is lower than in the above growing step.