Effect of bismuth excess on ferroelectric and piezoelectric properties of a (Na0.5Bi0.5)TiO3–BaTiO3 composition near the morphotropic phase boundary

(Na0.5Bix)0.93Ba0.07TiO3 (x = 0.500–0.510) ceramics were prepared by a citrate method and the structure and electrical properties of the ceramics were investigated. No significant change in both phase structure and microstructure with the Bi excess was found. A significant influence of the Bi excess on the ferroelectric and piezoelectric properties was detected at relative high excess Bi amounts. The variation of the electrical properties with excess Bi amount was rather slight when x ≤ 0.504, the specimens within this composition range exhibited large remanent polarizations (Pr) of 37.5–41.1 μC/cm2 at room temperature, a constant depolarization temperature (Td) of 85 °C and high piezoelectric constants (d33) of 171–176 pC/N. Higher excess Bi amounts (x ≥ 0.505) resulted in a considerable degradation of the ferroelectricity, a decrease of the depolarization temperature and a remarkable decline of the piezoelectricity. The variation of the electrical properties with excess Bi amount was qualitatively explained with respect to the formation of A-site vacancies originating from incorporation of the excess Bi into the perovskite structure.