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.