The high piezoelectricity and thermal stability of high-temperature piezoelectric ceramics BiFeO3–0.25BaTiO3–xBi0.5K0.5TiO3 near the MPB

Abstract

Lead-free high-temperature piezoelectric ceramics of 1 mol% Mn-doped (0.75 − x)BiFeO₃–0.25BaTiO₃–xBi_0.5K_0.5TiO₃ were prepared via a conventional solid-state sintering technique. The relationship between the phase structure and the electrical properties of this system was disclosed. A composition-induced structural transformation from rhombohedral to tetragonal was induced by increasing the BKT concentration. A morphotropic phase boundary (MPB) was formed at x = 0.010–0.015, which was confirmed by the Rietveld refinement and Raman spectroscopy deconvolution. In particular, the ceramic with x = 0.010 exhibits excellent performances with d₃₃ = 149 pC N⁻¹, k_p = 38%, P_r = 28.2 μC cm⁻² and T_C = 615 °C. The high-temperature piezoelectricity of the sample with the MPB (x = 0.010) was characterized by in situ Raman spectroscopy and in situ d₃₃ testing. The outstanding thermal stability of the crystal structure and the high depolarization temperature (T_d ∼ 570 °C) indicate that the BF–BT–BKT system is a promising candidate for lead-free high-temperature piezoelectric sensing.