Monoclinic crystal structure of polycrystalline Na0.5Bi0.5TiO3

Bismuth-based ferroelectric ceramics are currently under intense investigation for their potential as Pb-free alternatives to lead zirconate titanate-based piezoelectrics. Na0.5Bi0.5TiO3 (NBT), one of the widely studied compositions, has been assumed thus far to exhibit the rhombohedral space group R3c at room temperature. High-resolution powder x-ray diffraction patterns, however, reveal peak splitting in the room temperature phase that evidence the true structure as monoclinic with space group Cc. This peak splitting and Cc space group is only revealed in sintered powders; calcined powders are equally fit to an R3c model because microstructural contributions to peak broadening obscure the peak splitting.