Enhanced piezoelectric properties and electrical resistivity in CaHfO₃ modified BiFeO₃–BaTiO₃ lead-free piezoceramics

A number of CaHfO₃ modified BiFeO₃-0.33BaTiO₃ (BF-0.33BT-xCH) lead-free piezoceramics were fabricated through the solid-state sintering method and comprehensively investigated in this work. Under the optimal sintering temperature, all compositions display a typical perovskite structure in a pseudo-cubic phase with slightly larger lattice parameters as the CH content increases. The electrical resistivity is highly enhanced due to the addition of CH. Microstructures, including the grain morphology, core-shell structure, and chemistry inhomogeneities, are demonstrated upon different BF-0.33BT-xCH compositions. In particular, the core-shell structures with non-uniform element distributions in the compositions can be eliminated by adding sufficient CH content (x > 0.05). The highest saturation polarization (40.1 μC/cm²), remnant polarization (26.8 μC/cm²), and converse piezoelectric coefficient (290 pm/V) are achieved in the BF-0.33BT-0.01CH piezoceramic, which are significantly enhanced in comparison with the undoped BF-0.33BT piezoceramic. With further increasing the CH content, the piezoelectric properties of BF-0.33BT-xCH ceramics decline rapidly, and they start to exhibit characteristics of relaxor ferroelectrics.