Microstructure, ferroelectric, piezoelectric and ferromagnetic properties of BiFeO_3-BaTiO_3-Bi(Zn_(0.5)Ti_(0.5))O_3 lead-free multiferroic ceramics

摘要

Multiferroic ceramics of (0.70-x)BiFeO_3-0.30BaTiO_3-xBi(Zn_(0.5)Ti_(0.5))O_3 + 1 mol% MnO_2 with perov-skite structure were prepared by a conventional ceramic technique and the effects of Bi(Zn_(0.5)Ti_(0.5))O_3 doping and sintering temperature on the microstructure, multiferroic and piezoelectric properties of the ceramics were studied. All the ceramics possess a pure perovskite structure and no second phases can be detected. After the addition of a small amount of Bi(Zn_(0.5)Ti_(0.5))O_3 (x ≤ 0.05), the ferroelectric and piezoelectric properties of the ceramics are improved and the grain growth is promoted. However, excess Bi(Zn_(0.5)Ti_(0.5))O_3 (x ≥ 0.10) retards the grain growth, degrades the ferroelectricity and piezoelectricity, and induces two dielectric anomalies at high temperature. The ceramics can be well sintered at the very wide range of low sintering temperatures (880-980 ℃) and exhibit good densification (relative density: 96.2-98.4 %) and strong electric insulation. The increase in the sintering temperature promotes the grain growth and improves the ferroelectricity of the ceramics. The ceramic with x = 0.05 sintered at 880-980 ℃ possesses improved ferroelectric and piezoelectric properties with remanent polarizations P_r of 21.9-28.1 μm/ cm2, piezoelectric constants d_(33) of 125-139 pC/N and planar electromechanical coupling factors k_p of 30.1-32.4 %, and high Curie temperatures T_C of 523-565 ℃. A weak ferromagnetism with remanent magnetizations M_r of 0.0411-0.0422 emu/g and coercive fields H_c of 1.70-1.99 kOe were observed in the ceramics with x = 0-0.025.