Enhanced electric field induced strain of Hf4+ doped 0.67BiFeO3-0.33BaTiO3 lead-free piezoelectric ceramics

Abstract

High-temperature solid-phase method were used to prepare lead-free piezoelectric ceramics of 0.67BiFeO₃-0.3BaTi_1 − xHf_xO₃ and the effects of B-site Hf⁴⁺ doping on the microstructure, dielectric properties, and ferroelectric properties of the ceramics were investigated systematically. The results have shown that partial substitution of Hf⁴⁺ for Ti⁴⁺ did not cause significant changes in the phase structure, and the components remained in the multi-phase boundary region where tetragonal and rhombohedral structures coexisted, resulting from the same electricity price and small differences of Hf⁴⁺/Ti⁴⁺ ion radius. However, doping with Hf⁴⁺ can effectively increase the content of Fe³⁺ and reduce the leakage current of BFO-BT binary system. The Curie temperature of BFO-BT-0.05Hf ceramic is 387 ℃, which effectively maintaining the high Curie point of the BFO-BT binary system. The undoped BFO-BT exhibits a typical ferroelectric P-E hysteresis loop, with P_r=26.47µC/cm² and E_C=34.54 kV/cm. After appropriate modification with Hf⁴⁺, the ferroelectric properties of the BFO-BT system were significantly improved, with P_r of 33.34 µC/cm² and E_C of 31.90 kV/cm for BFO-BT-0.05Hf. The strain of BFO-BT-0.05Hf ceramic at room temperature is 0.19%. Meanwhile, the electric field induced-strain of the ceramic at 125 ℃ and 80 kV/cm is 0.43%, and the high-field piezoelectric coefficient (d₃₃^*) is 543 pm/V.