PEROVSKITES (CA1-XSRX) (CA1/3NB2/3)O3

New perovskite-like compounds (Ca1-xSrx)(Ca 1 3Nb 2 3)O3 were prepared and investigated by X-ray and electron diffraction. They exhibit two low-temperature monoclinic forms, M1 and M2, and at high temperature, two orthorhombic forms, O1 and O2, and a tetragonal one, Q. M1 and M2 oxides agree with a layer-like ordering of Ca and Nb ions in a 1:2 manner on the octahedral and 12-fold sites. O1 and O2 forms are characterized by a random distribution of metal ions. The tetragonal form Q was interpreted as a 1:1 type of order, with transition structure between O2 and M2. A number of twinning phenomena, in agreement with the suggested ordering state, was observed by electron microscopy. © 1979.