Role of sodium deficiency on the relaxor properties of Bi1/2Na1/2TiO3-BaTiO3

The influence of A-site deficiency on the relaxor properties in the lead-free (1-x)(Bi1/2Na1/2)TiO3-xBaTiO3 solid solution system was studied by intentionally reducing Na content in reference to the stoichiometric compositions. We observed that for all compositions, the higher the level of Na deficiency was, the lower the transition temperature from a ferroelectric to relaxor state became. The compositions with intermediate BaTiO3 contents (x = 0.06, 0.09, 0.13, and 0.40) showed sprout-shaped strains and pinched polarization curves at room temperature, indicating a crossover from a non-ergodic relaxor to ergodic relaxor state above a certain level of Na deficiency. We demonstrate that the presence of recently proposed oxygen octahedral tilt disorder as a prerequisite for the relaxor features in this system is not necessarily true, but the presence of stress-field-induced defect dipoles matters. A transmission electron microscopy confirmed that micro domains break down into nano domains with increasing Na deficiency level.