Structures, dielectric properties and AC impedance characteristics of BiFeO₃–BaTiO₃ high-temperature lead-free piezoceramics synthesized by the hydrothermal method

Abstract

Among the lead-free piezoceramics, ([Formula: see text])BiFeO[Formula: see text]BaTiO 3 (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature ([Formula: see text]C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO 3 and BaTiO 3 , and then the mixed powder compacts with the chemical composition of 0.7BF–0.3BT were sintered under pressureless conditions. The influence of the hydrothermal reaction times (12–24[Formula: see text]h) of BiFeO 3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO 3 and BiFeO 3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO 3 increased, the dielectric properties as well as the temperature stability of the 0.7BiFeO 3 –0.3BaTiO 3 ceramics also improved. At the condition of a hydrothermal reaction time of 24[Formula: see text]h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant ([Formula: see text]C between RT and [Formula: see text]C) and the highest Curie temperature ([Formula: see text]C at 100[Formula: see text]kHz). Moreover, at high temperatures, it exhibits a higher AC impedance than others. The calculating result based on the resistive constant-phase-element model (R-CPE) circuit model showed that the grain boundary of the 0.7BF–0.3BT ceramics contributes more resistance to the conductivity at high temperatures. In summary, the hydrothermal reaction proved to be a useful way that achieves the preparation of single-phase 0.7BF–0.3BT ceramics with improved electrical properties.

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