Microstructure and Electrical Properties of Nonstoichiometric 0.94(Na0.5Bi0.5+x)TiO3-0.06BaTiO3 Lead-Free Ceramics

0.94(Na0.5Bi0.5+x)TiO3-0.06BaTiO(3) (x=-0.04, 0, 0.02; named NB0.46T-6BT, NB0.50T-6BT, NB0.52T-6BT, respectively) lead-free piezoelectric ceramics were prepared via the solid-state reaction method. Effects of Bi3+ nonstoichiometry on microstructure, dielectric, ferroelectric, and piezoelectric properties were studied. All ceramics show typical X-ray diffraction peaks of ABO(3) perovskite structure. The lattice parameters increase with the increase in the Bi3+ content. The electron probe microanalysis demonstrates that the excess Bi2O3 in the starting composition can compensate the Bi2O3 loss induced during sample processing. The size and shape of grains are closely related to the Bi3+ content. For the unpoled NB0.50T-6BT and NB0.52T-6BT, there are two dielectric anomalies in the dielectric constant-temperature curves. The unpoled NB0.46T-6BT shows one dielectric anomaly accompanied by high dielectric constant and dielectric loss at low frequencies. After poling, a new dielectric anomaly appears around depolarization temperature (T-d) for all ceramics and the T-d values increase with the Bi3+ amount decreasing from excess to deficiency. The diffuse phase transition character was studied via the Curie-Weiss law and modified Curie-Weiss law. The activation energy values obtained via the impedance analysis are 0.69, 1.05, and 1.16eV for NB0.46T-6BT, NB0.50T-6BT and NB0.52T-6BT, respectively, implying thechange in oxygen vacancy concentration in the ceramics.The piezoelectric constant, polarization, and coercive field of the ceramics change with the variation in the Bi3+ content. The Rayleigh analysis suggests that the change in electrical properties of the ceramics with the variation in the Bi3+ amount is related to the effect of oxygen vacancies.