Study On Structure, Piezoelectric And Multiferroic Properties Of Metal Oxides Doped BiFeO₃-BaTiO₃ Room Temperature Multiferroic Ceramics

Multiferroic materials possess simultaneously two or more ferroics(ferroelectric, ferromagnetic and ferroelastic properties, etc.). Bi Fe O3, as typical single-phase multiferroic material with high Curie temperature(TC = ~1100 K) and Néel temperature(TN = ~640 K), possesses simple perovskite structure and exhibits simultaneously ferroelectricity and ferromagnetism at room temperature. It has been paid considerable attention in recent years in the field of condensed physics and material science. Bi Fe O3-based ceramics show the magnetoelectric coupling effect due to its electric order and magnetic order, and thus multifunctionaldevicesbased on Bi Fe O3-based materials with excellent performance can be developed. However, some obstacleslimit the applications of Bi Fe O3 such as the difficultity of synthesis for the pure phase, large leakage current and no macroscopic ferromagnetism at room temperature. Adding ABO3 type perovskite titanate into Bi Fe O3 to form Bi Fe O3-based solid solution can improve the insulation of the material and inhibit thegeneration of impurity phase. As classic Bi Fe O3-based solid solution, 0.7Bi Fe O3-0.3Ba Ti O3 shows excellent piezoelectric and multiferroic properties, but there are little work on the effects of metal oxide doping on the structure, piezoelectric and multiferroic properties of the materials. In this work, the microstructure, piezoelectric and multiferroic properties of metal oxides(Fe2O3, Co2O3, Ni O and Nb2O5) doped 0.7Bi Fe O3-0.3Ba Ti O3 ceramics were systematically investigated.The main results are listed as following:(1) 0.7Bi Fe O3–0.3Ba Ti O3 + 1 mol% Mn O2 + x mol % Ni O(x = 0-3.0) multiferroic ceramics were successfully prepared by a conventional oxide-mixed method, and the effects of Ni O doping on phase structure, microstructure, piezoelectric and multiferroic properties of the ceramics were studied. All the ceramics exhibit pure rhombohedral perovskite phase and no second phases can be detected. The grain growth is inhibited with Ni O doping and the insulation, piezoelectric, ferroelectric and ferromagnetic properties are improved. The ceramic has high resistivity(~6.30×109 ?·cm), strong ferroelectricity(Pr = 20 μC/cm2), excellent piezoelectricity(d33 = 151 p C/N, kp = 35%) and ferromagnetism(Mr = 0.117emu/g) with x = 0.5.(2) 0.7Bi Fe O3-0.3Ba Ti O3 + 1mol % Mn O2 + ymol% Co2O3(y = 0-3.0) multiferroic ceramics were fabricated by an ordinary sintering technique. All the ceramics exhibit rhombohedral perovskite structure and show excellent electrical insulation performance(6.62×109 ?·cm, 2.17×10-5 A/cm2). Improved ferroelectric and ferromagnetic properties are observed. The ceramic with y = 1.0 has the excellent piezoelectricity(d33 = 134 p C/N, kp = 0.33%) and the optimal ferromagnetism(Mr = 0.191 emu/g). Best ferroelectricity(Pr = 23.0 μC/cm2) of the ceramic is obtained at y = 1.5.(3) 0.7Bi Fe O3-0.3Ba Ti O3 + 1mol % Mn O2 + z mol% Fe2O3(z = 0-3.0) multiferroic ceramics were fabricated by the traditional solid state reaction method. All the ceramics show R3 c rhombohedral perovskite structure and no any impurity phase can be detected. All the ceramics exhibit good electrical insulation(R ~109 ?·cm). Enhanced piezoelectric property(d33 = 139 p C/N) is obtained in the ceramicwith z = 1.0, Remanent magnetization Mrincreasesmonotonically with z increasing, and optimalferromagnetism(Mr = 0.401emu/g) is obtained with z = 3.0.(4) The Bi0.7Ba0.3(Fe0.7Ti0.3)1-uNb0.66uO3+ 1 mol % Mn O2(u = 0-0.02) ceramics were prepared by a conventional solid-state reaction method. All the ceramics exhibit distorted rhombohedral perovskite structure. For the present ceramics, uniform grains and clearly demarcated grain boundaries are observed with small amount of Nb doping, however, the grain growth is inhibited with excessive ions doping. All the ceramics show low leakage current(J ~10-5-10-4 A/cm2) and high resistivity(R ~109-1010 ?·cm). The ferroelectricity and piezoelectricity of the ceramics decreased with Nb doping(Pr and Ec decreased from 19.7 μC/cm2 and 3.7 k V/mm to 3.1 μC/cm2 and 2.4 k V/mm, d33 decreased from 133 p C/N to 19 p C/N). However, The Curie temperature TC of the ceramics slightly increased from 578 oC to 603 oC with u increasing from 0 to 0.0025.