Low temperature synthesis route and structural characterization of (Bi0.5A0.5)(Sc0.5Nb0.5)O3 (A = K+ and Na+) perovskites

Abstract

Two new perovskites, (Bi_0.5A_0.5)(Sc_0.5Nb_0.5)O₃ where A = K⁺ and Na⁺, have been made phase pure for the first time. The synthesis procedure that prevented the formation of pyrochlore impurities is described. B-site ordering in A = K⁺ is successfully achieved by prolonged heating. Combined Rietveld refinement on synchrotron X-ray diffraction and neutron diffraction data is used to determine the complex average structure of these materials. A = Na⁺ crystallizes in the tetragonal P4/mbm space group and has disordered a⁰a⁰c⁺ rotations of BO₆ octahedra. A = K⁺ crystallizes in the cubic Pmm space group, but shows local A-site displacements in the [100] direction. Both materials are highly disordered but illustrate the potential of (A)NbO₃-BiScO₃ solid solutions as useful piezoelectrics or relaxors.