Orthorhombic to cubic phase transition in La1-XCaXMnO3 perovskites

The variations of the polycrystalline X-ray diffraction patterns of La1-xCaxMnO3 perovskites (x = 3/8, 1/2, 2/3) with composition and temperature have been studied. When the temperature increased to 750 or 900 degreesC, a phase transition from orthorhombic to cubic perovskites was observed for the first time, This phase transition confirms further that the orientation domains in La1/3Ca2/3MnO3 are induced by a cubic to orthorhombic phase transition, but not by charge ordering. Moreover, the unit cell parameters a(O), b(O) and c(O) of these orthorhombic perovskites at room temperature, and also a(p) of these cubic perovskites at high temperature, decrease with increasing x.