Phase transition behavior and high piezoelectric properties in lead-free BaTiO₃-CaTiO₃-BaHfO₃ ceramics

The transition behavior, structural changes, and electric properties of lead-free (1-x)Ba(Hf_0.16Ti_0.84)O₃ -x(Ba _0.70Ca_0.30)TiO₃ (BCHT) ceramics fabricated by the conventional solid-state reaction method are investigated in this study. A complete phase diagram of BCHT system has been proposed based on their dielectric behavior. It is found that BHCT ceramics undergo a complicated phase evolution, driven by Ca and Hf contents. The results clearly demonstrate that high electric properties are achieved in the ferroelectric orthorhombic- tetragonal phase boundary near the composition with x = 0.48, which could be adjusted by the contents of Ca and Hf in the composition. The optimum composition shows enhanced properties with dielectric constant ε _r = 2889 (at room temperature, 1 kHz), high piezoelectric coefficient d₃₃ = 410 pC/N, and electromechanical coupling factor k_p = 0.47, and a relative high Curie temperature of 106 °C. This investigation yields a sight to understand different phase transition mechanisms of enhanced piezoelectricity for the system.