ALBERT

Description: 0.94(Na 0.5 Bi 0.5+ x )TiO 3 –0.06BaTiO 3 ( x  = −0.04, 0, 0.02; named NB 0.46 T-6BT, NB 0.50 T-6BT, NB 0.52 T-6BT, respectively) lead-free piezoelectric ceramics were prepared via the solid-state reaction method. Effects of Bi 3+ 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 Bi 3+ content. The electron probe microanalysis demonstrates that the excess Bi 2 O 3 in the starting composition can compensate the Bi 2 O 3 loss induced during sample processing. The size and shape of grains are closely related to the Bi 3+ content. For the unpoled NB 0.50 T-6BT and NB 0.52 T-6BT, there are two dielectric anomalies in the dielectric constant–temperature curves. The unpoled NB 0.46 T-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 Bi 3+ 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 1.16 eV for NB 0.46 T-6BT, NB 0.50 T-6BT and NB 0.52 T-6BT, respectively, implying the change in oxygen vacancy concentration in the ceramics. The piezoelectric constant, polarization, and coercive field of the ceramics change with the variation in the Bi 3+ content. The Rayleigh analysis suggests that the change in electrical properties of the ceramics with the variation in the Bi 3+ amount is related to the effect of oxygen vacancies.