Evidence for a non-rhombohedral average structure in the lead-free piezoelectric material Na_0.5Bi_0.5TiO₃

The potential lead-free piezoelectric material sodium bismuth titanate, Na_0.5Bi_0.5TiO₃, was investigated by means of high-resolution single-crystal X-ray diffractometry. The splitting of Bragg peaks observed in the high-resolution reciprocal-space maps suggests that the average structure of Na_0.5Bi_0.5TiO₃ has lower than rhombohedral symmetry. This observation is contrary to the commonly adopted model, which has followed from many previous analyses of neutron and X-ray powder diffraction data.