| In recent years, multiferroic materials get more and more attention from researchers for its great potential for technological applications in multifunctional sensors, actuators and data storage. Among the multiferroic materials, bismuth ferrite BiFeO3 (abbreviated as BFO) is the only material that exhibits both magnetic and ferroelectric properties at room temperature. However, the large leakage current which lead to poor ferroelectric properties and an incommensurate cycloidal spin structure that cancels the net macroscopic magnetization limit its application. In this work, with BiFeO3 as the research object, (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 (abbreviated as BCZT) and BFO form solid solution in order to enhance the resistivity, which can correctly measure the ferroelectricity and gain saturation polarization and break the cycloidal spin structure of the BFO matrix, thus releasing the locked magnetization. In this study, (1-x) BiFeO3-x (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 ceramics [(1-x) BFO-x BCZT)] were synthesized to investigate their dielectric, ferroelectric, piezoelectric and magnetic properties and discuss its physical mechanism. The main results are as follows:1. Polycrystalline (1-x) BiFeO3-x (Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 [(1-x) BFO-x BCZT)] ceramics were fabricated by a solid state reaction method. The phase structure, microstructure, and dielectric, ferroelectric and magnetic properties of the (1-x) BFO-x BCZT ceramics were systematically investigated. The crystal structure of the (1-x) BFO-x BCZT ceramics transformed from rhombohedral to pseudocubic with increasing x. A morphotropic phase boundary existed at the composition of 0.20≤x≤0.30. The average grain size of the ceramics initially increased to a maximum at x= 0.30 and then decreased. The frequency dependence of dielectric constant and complex impedance plots indicated an electrically heterogeneous microstructure for x< 0.20 caused by the coexistence of Fe2+and Fe3+. Tm and em decreased with increasing x for 0.25≤ x≤0.80, and the hysteresis loops (P-E) became slimmer with increasing x. All samples presented weak ferromagnetic ordering, indicating that the substitution of BCZT into the BFO matrix released its potential magnetization. The optimal ferroelectric and magnetic properties, Pr of 22.7-2.3 μC/cm2 and Mr of 0.0394-0.0744 emu/g, were obtained at 0.30≤x≤0.35.2. The 0.7BiFeO3-0.3(Ba0.85Ca0.15)(Zr0.10Ti0.90)O3 +xwt%MnO2(x=0-0.7) multiferroic ceramics have been prepared. The effect of Mn doping on phase structure, microstructure, dielectric, piezoelectric as well as magnetic properties have been intensively investigated. It is found that all the ceramics are pseudocubic, whereas the grain size decreases with the increase of x. As x increases, the relaxor degree increase, the ferroelectricity and piezoelectricity weaken monotonically. A small amount of Mn doping (x≤0.3) can break the cycloidal spin structure of the BFO matrix, thus releasing the locked magnetization. The highest remnant magnetization Mr=0.1995 emu/g was observed for composition x=0.4.3. The 0.7(Bi1-xLax)FeO3-0.3(Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (x=0-0.04)+0.4 wt% MnO2 multiferroic ceramics have been prepared by a solid state reaction method. The effect of La substituting on phase structure, microstructure, dielectric, piezoelectric as well as magnetic properties have been intensively investigated. It is found that all the ceramics are pseudocubic. The average grain size increase firstly, reaching the maximum near x= 0.01 or x=0.02, and then decreases. The optimum of the ferroelectric, piezoelectric and resistivity properties are Pr= 6.47 μC/cm2, d33= 30 pC/N, p=1.3×109Ω·cm atx=0.01, the depolarization temperature Td which indicating high-temperature stable piezoelectric properties is 275℃, while the magnetic property is Mr=0.1610 emu/g. Therefore, the ceramics is not only an excellent ferroelectric, piezoelectric material, but also an excellent magnetic material. It has a promising application on information technology, sensor and spintronic devices. |
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