Insights into the Structure and Electrical Properties of Bi0.5Na0.5TiO3–PbTiO3 Single Crystals near the Morphotropic Phase Boundary

Abstract

Herein, high-quality 0.88(Bi_0.5Na_0.5)TiO₃–0.12PbTiO₃ (BNT–12PT) single crystals were successfully grown by the flux method for the first time, achieving a maximum volume of 9.3 × 9.1 × 3.3 mm³. Furthermore, the phase structure, electrical properties, and domain structure of single crystals were systematically investigated. The average phase structure of as-grown single crystals exhibits a rhombohedral–tetragonal (R3c–P4mm) coexistence. These specimens achieve considerable piezoelectric properties (d₃₃ ∼ 212 pC/N) without deteriorating the depolarization temperature (T_d ∼ 206 °C). The appearance of the stripe-shaped domain structure before poling and the first-cycle ferroelectric and electrostrain responses reveal that the initial state of the BNT–12PT single crystal is a long-range ferroelectric state. In addition, a rapid rise in the piezoelectric coefficient from 248 to 348 pC/N, as well as a significant increase in maximum strain from 0.11% to 0.53%, is observed within the temperature range of 100 °C to T_d, and the corresponding modification in relative permittivity and frequency dispersion tends to coincide. Furthermore, the disappearance of the rhombohedral phase near 300 °C was confirmed by the observation of the optical domain structure. This work further deepens the understanding of the structure and electrical properties of the BNT–PT single crystals.