RELATIONS BETWEEN OXYGEN DEFICIENCY AND STRUCTURES IN THE LA-SR-CU-O SYSTEM .2. A NEW OXYGEN-DEFICIENT PHASE (LA, SR)4CU4O10

We report the synthesis and the structural properties of a new oxygen-deficient perovskite with the formula (La1-xSrx)4Cu4O10 (x = 0.1429) (Sr/La = 1/6): 4-4-10). It crystallizes in an orthorhombic cell with the parameters a ≈ 2 2ap, b ≈ 2ap, and c ≈ ap, where ap means the cell constant of an ideal cubic perovskite. According to the crystal structure which has been refined in the space group Pbam by Rietveld analysis of powder X-ray diffraction (XRD), it has the same structure as CaMnO2.5, and lanthanum and strontium ions in the structure are statistically distributed as well as the other compounds, (La1-xSrx)8Cu8O20 (0.16 ≤ x ≤ 0.24:8-8-20) and (La1-xSrx)5Cu5O13 (x = 0.1666 (Sr/La = 1/5): 5-5-13). This newly found 4-4-10 compound, however, is constituted by only one type of Cu-O polyhedron, i.e., CuO5 pyramids, while the 8-8-20 and the 5-5-13 compounds include CuO6 octahedra and/or CuO4 squares in the structure as well. TG-DTA study and XRD measurement at high temperature revealed the structural phase transition of 4-4-10 to 8-8-20 around 550°C without any gain or loss of oxygen. Some physical properties are also reported. © 1993 Academic Press, Inc.