Phase boundary atx=0.03and its anomalous influence on the structure and properties in the lead-free piezoelectric (1−x)Na_1/2Bi_1/2TiO₃−(x)BaTiO₃

Abstract

The complexity associated with local structures continues to pose challenges with regard to the understanding of the structure-property relationship in Na_1/2Bi_1/2TiO₃ -based lead-free piezoceramics. (1−x) Na_1/2Bi_1/2TiO₃−( x ) BaTiO₃ is an extensively studied system because of its interesting piezoelectric properties. Recently, a room temperature phase boundary was reported at x = 0.03 in this system [Ma et al., Adv. Funct. Mater. 23, 5261 (2013)]. In the present work we have examined this subtle phase boundary using x-ray diffraction, neutron diffraction, dielectric measurements as a function of composition (x < 0.06 ) , temperature, and electric field. Our results show that this boundary separates an R3c + Cc -like structural state for x < 0.03 from an R3c + cubiclike structural state for 0.03 ≤ x ≤ 0.05 in the unpoled specimens. This phase boundary is characterized by an anomalous reduction in the depolarization temperature, and a suppression of the tetragonal distortion of the high temperature P4bm phase. Our results also provide the clue to understand the pathway leading to the cubiclike structure of the critical composition x = 0.06 , known for its highest piezoelectric response.