Phase stability of the A2Cu3O4X2 (A = alkaline-earth; X = halogen) system

Stability of A(2)Cu(3)O(4)X(2) (A = Sr, Ba; X = Cl, Br) of the 2342 phase with the Cu3O4 plane, which is composed of the Cu(1)O-2 and extra Cu(2) sublattices, has been studied in the temperature range between 600 degrees C and 950 degrees C. Polycrystalline samples of the composition Sr2-xBaxCu3O4Cl2-yBry were prepared by the solid-state reaction method. From the powder x-ray diffraction analysis, we have made the phase diagram (x vs. y vs, heat-treatment-temperature). It has been found that the 2342 phase becomes stable with increasing x and y at high heat-treatment-temperatures instead of a mixture of CuO and the A(2)CuO(2)X(2) (2122) phase with the CuO2 plane. These results can be explained in terms of the structural matching between the Cu3O4 plane and the A(2)X(2) layer.