Temperature dependence of the dielectric and piezoelectric properties of xBiFeO₃–(1 − x)BaTiO₃ ceramics near the morphotropic phase boundary

Lead-free and high-temperature piezoelectric ceramics of xBiFeO₃–(1 − x)BaTiO₃-1.0 mol% MnO₂ (0.67 ≤ x ≤ 0.78) (xBF–(1 − x)BT-Mn) were fabricated by the conventional solid-state reaction method, and their high-temperature dielectric, piezoelectric and ferroelectric properties near the morphotropic phase boundary were studied systematically. XRD analysis revealed that xBF–(1 − x)BT-Mn ceramics exhibited pure perovskite structure, and the phase was driven by composition variation from the pseudo-cubic (0.67 ≤ x < 0.70) to rhombohedral (0.70 ≤ x ≤ 0.78). The dielectric constant ε _r (1 kHz), dielectric loss tanδ (1 kHz), Curie temperature T _C, depolarization temperature T _d, piezoelectric constant d ₃₃, remnant polarization P _r (60 kV/cm) and room temperature planar electromechanical coupling factor k _p of xBF–(1 − x)BT-Mn ceramics of x = 0.70 were 740, 0.045, 487, 430 °C, 35.5 μC/cm², 177 pC/N and 0.37, respectively. The unipolar strain and high field strain coefficient d ₃₃ ^* of xBF–(1 − x)BT-Mn ceramics with x = 0.70 increased up to 0.26% and 652 pm/V at 180 °C. Temperature dependence of ε _r, tanδ and k _p of xBF–(1 − x)BT-Mn ceramics with x = 0.75 was stable from room temperature even up to 500 °C. These results indicated that xBF–(1 − x)BT-Mn ceramics were promising candidates for high-temperature lead-free piezoelectric applications.