Abstract: A method for producing a transparent white large single crystal of zinc oxide includes the steps of mixing zinc oxide as a solute with molybdenum oxide as a solvent, heating the resultant mixture till fusion, and thereafter keeping the temperature of the produced melt intact or lowering the temperature thereof, thereby inducing deposition and growth of a microcrystal represented by the general formula, ZnO, on a seed crystal or substrate.

Abstract: PrBa.sub.2 Cu.sub.3 O.sub.Y exhibiting superconductivity is provided by a method including the steps of preparing a solvent consisting of a mixture of praseodymium oxide, at least one of barium oxide and barium carbonate, and copper oxide at a mixing ratio of between 1:3:5 and 1:8:20, disposing the solvent between a feed rod of PrBa.sub.2 Cu.sub.3 O.sub.7 formed to a high density and a seed crystal, heating the solvent to a temperature of 880.degree.-980.degree. C. in an atmosphere of an inert gas of at least one of argon and nitrogen mixed with 0.01-2% oxygen to form a floating solvent zone, moving the floating solvent zone toward the feed rod at 0.1-1.0 mm/hr under a temperature gradient at the solid-liquid interface of 25.degree.-35.degree. C./mm to precipitate single crystal on the seed crystal, and heat-treating the single crystal obtained in an atmosphere containing not less than 15% oxygen. Another aspect of the invention provides a superconducting device including the superconducting PrBa.sub.2 Cu.

Abstract: Lanthanum cuprate, La.sub.2 CuO.sub.4, is a superconductive oxide. In order to prepare a single crystal of lanthanum cuprate, the phase diagram of La.sub.2 O.sub.3 -CuO system is determined utilizing their differential thermal analysis and X-ray diffractometry. Cu oxide and at least one of lanthanum oxide and lanthanum carbonate are mixed in the molar ratio of 71.1-92.9:28.9-7.1. The resulting mixture is heated to be molten. While slowly cooling the melt, nuclei of La.sub.2 CuO.sub.4 precipitate from the melt, growing to single crystals in the melt. As a result, large scale single crystals are prepared.

Abstract: Lanthanum cuprate, La.sub.2 CuO.sub.4, is a superconductive oxide. In order to prepare a single crystal of lanthanum cuprate, the phase diagram of La.sub.2 O.sub.3 -CuO system is determined utilizing their differential thermal analysis and X-ray diffractometry. Cu oxide and at least one of lanthanum oxide and lanthanum carbonate are mixed in the molar ratio of 71.1-92.9:28.9-7.1. The resulting mixture is heated to be molten. While slowly cooling the melt, nuclei of La.sub.2 CuO.sub.4 precipitate from the melt, growing to single crystals in the melt. As a result, large scale single crystals are prepared.