Phase diagram of SrOCaOCuO ternary system

Abstract

The phase diagrams of SrOCuO, SrOCaO and CaOCuO binary systems, the room temperature section of SrOCaOCuO ternary system, vertical section of Sr2CuO3Ca2CuO3 system and crystallographic parameters of compounds in SrOCaOCuO system are investigated by X-ray powder diffraction and thermal analysis. There sre three binary compounds: Sr2CuO3, SrCuO2 and Sr3Cu5O8 in SrOCuO system. They are all formed by peritectic reactions and all of them belong to orthorhombic lattice. The space group of Sr2CuO3 is Immm with lattice parameters: a = 1.2708 nm, b = 0.3913 nm, c = 0.3502 nm. The space group of SrCuO2 is Cmcm with lattice parameters: a = 0.3573 nm, b = 1.6333 nm, c = 0.3915 nm. Sr3Cu5O8 has a face-centre lattice with parameters: a = 1.3402 nm, b = 1.1470 nm, c = 0.3939 nm. In CaOCuO system only one compound Ca2CuO3 is observed. Ca2CuO3 is isostructural with Sr2CuO3. Its lattice parameters are a = 1.2243 nm, b = 0.3779 nm, c = 0.3258 nm. The continous solid solution is formed in the CaOSrO system. The section at room temperature in SrOCaOCuO system can be divided into four two-phase regions and two three-phase regions. Solid solutions of Sr2(1-x)Ca2xCuO3 (x = 0 to 1), Sr1-xCaxCuO2 (x ⩽ 0.65) and Sr3(1-x)Ca3xCu5O8 (x ⩽ 0.50) are formed. The lattice parameters of solid solutions decrease with increasing Ca-contents.