Crystallochemical Studies on the High Temperature Superconductors La2-xMxCuO4-y (M=Ba and Sr)

Abstract

High temperature superconductors La_2-x M _x CuO_4-y (M=Ba and Sr) with the K₂NiF₄ structure were synthesized by solid state reaction and characterized by X-ray diffraction, electron microscopy, IR measurements and thermogravimetry. Anomalous behavior of unit cell parameters was confirmed. Electron diffraction study of the orthorhombic La₂CuO₄ revealed weak forbidden spots for Fmmm symmetry, suggesting a space group of lower symmetry. One of three IR bands observed in La₂CuO₄ rapidly disappeared around x=0.1. Highest superconducting transition temperature was found to be 38.0 K in La_1.85Sr_0.15CuO_3.96.