Abnormal piezoelectric and dielectric behavior of 0.92Na_0.5Bi_0.5TiO₃-0.08BaTiO₃ induced by La doping

Properties and phase structures of lead-free piezoelectric ceramics 0.92Na_0.5Bi_0.5TiO₃-0.08BaTiO₃ (NBT-BT) modified with La₂O₃ have been studied. Because of the different valence and ionic radius between La³⁺ and the exchangeable A-site ions, the lattice distortion and arrangement in the modified compounds can be expected, which will directly influence the phase composition and electrical characteristics of NBT-BT. Differing from familiar frame of gradual variability going with adulteration, NBT-BT doping 0.2–1.0 at.% La₂O₃ presents an abnormal increase of dielectric constant and a dramatic vanish of piezoelectricity. Further study on the relaxor property and domain structure implies that it originates from a typical relaxor-to-antiferroelectric crossover phase transition. However, a larger addition of La₂O₃ could rejuvenate the ferroelectricity and piezoelectricity of NBT-BT, correlating well with the model of competing ferro- and antiferroelectric interactions and metastable intermediate phase behavior in the morphotropic phase boundary region of complex perovskites.