COMPOUNDS AND PHASE-RELATIONS IN THE SRO-CAO-CUO SYSTEM UNDER HIGH-PRESSURE

The phase relation in the ternary SrO-CaO-CuO system under high pressu re has been studied by means of powder X-ray diffraction, electron dif fraction, and high-resolution electron microscopy. In the SrO-CuO syst em studied in a pressure and temperature range of 1.7-8 GPa and 850-11 50 degrees C, Sr2CuO3, SrCuO2(II), Sr2Cu3O5, and SrCu2O3 form, Tn the CaO-CuO system, CaCuO2 (I) of the infinite-layer type forms at 3-5 GPa and 1050-1200 degrees C. This compound undergoes a polymorphic struct ural transformation into another high-pressure form CaCuO2 (II) which comprises a new type of CuO2 planes. A structural model built on the b asis of electron diffraction and high-resolution electron microscopy i s presented, The ternary phase diagram at 4 GPa and l(sic)20 degrees C is presented. (C) 1997 Academic Press.