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

Among the lead-free piezoceramics, (1-x)BiFeO3-xBaTiO(3) (BF-BT) is considered a promising candidate for high-temperature piezoelectric materials owing to its high Curie temperature (T-C>400(degrees)C) and good electromechanical properties. In this work, the hydrothermal synthesis method was used to prepare the precursor powders of BiFeO3 and BaTiO3, 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 (12-24h) of BiFeO3 on the structures and electric properties of the sintered ceramics was instigated. First, all the samples synthesized with the tetragonal BaTiO3 and BiFeO3 powders were identified with relatively stable dielectric properties. As the hydrothermal reaction time to synthesize BiFeO3 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 24h, the sample obtained possesses both the lowest temperature coefficient of dielectric constant (Tk(epsilon)=1.53x10(-2)/C-degrees between RT and 300(degrees)C) and the highest Curie temperature (T-C=471(degrees)C at 100kHz). 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.