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. ${\text{Na}}_{0.5}{\text{Bi}}_{0.5}{\text{TiO}}_3$ (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.