Syntheses,Structures And Properties Of Novel Multiferroics Oxides

Multiferroics are compounds in which the ferroelectric(FE)(or antiferroelectric(AFE)),ferromagnetic(FM)(or antiferromagnetic(AFM))order and ferroelastic order coexist simultaneously in certain temperature range. The multiferroics researched recently are the materials with both FE order and magnetic order structures, and the coupling effects between these two order structures(Magnetoelectric(ME)effect) triggered a lot of excitement. The materials which have the ME effect-the induction of magnetization by means of an electric field and induction of polarization by means of a magnetic field-are defined as the magnetoelectrics. The first observation of the ME effect triggered a lot of excitement because of the obvious potential of the cross-correlation between the magnetic and electric properties of matter for technical applications. The ferroelectrtomagnets, in which FE ordering and magnetic spin ordering coexist spontaneously at low temperature, have been the object of intensive theoretical and experimental studies from the 60-70's last century for its connection with the finding out this kind of material and their are some special properties of physics own to ME coupling. By ME coupling, the application of an electric field or FE polarization can change one or more of the parameters governing the magnetic behavior of the system. Correspondingly, being possible magnetostrictive effect or electron-phonon interaction, the fluctuation of spin ordering may lead to a dielectric anomaly and FE relaxation.This study searches for new solid state oxide materials with perovskite and perovskite-related structures by two strategies. The first one is by systematically research of subsolidus phase equilibria of ternary oxides; the second is by rational design of new compounds according to the structural features of deficient pervoskite, double pervoskite etc. Then we use diffraction techniques(including Powder X-ray Diffraction, Electron Diffraction and Neutron Diffraction), Electron Microscopy techniques combined with other measurements to determine their crystal structures, as well as their phase transitions, electrical and magnetic properties. And then, we studied the relationship between the crystal structures and their properties. The results are following:The series BaBi_1-xTa_xO₃ (0≤x≤0.5) have been synthesized, by the combining use of the CBED, powder X-ray and neutron diffraction, the space group of them is determined to be P1. However, the current hysteresis measurement does not show they are ferroelectrics; Synthesized a new solid solutions Sr_xBi_1-xMn_xFe_1-xO₃(0≤x≤1.0). From doping, make the paramagnetism BiFeO₃ transform into ferromagnetism in the room temperature ; Study the phase relationship of the Fe₂O₃-PbO-Ta₂O₅ and Fe₂O₃-Bi₂O₃-Ta₂O₅ systems. We find a large pyrochlore phase field in these ternary phase diagrams, the magnetization and ferroelectricity of the pyrochlore phase were mainly studied. We find two new isostructuralism compounds Fe_0.1Bi_2.4Ta_4.5O₁₅ and Bi_1.02Ta_1.98O₄ in the Fe₂O₃-Bi₂O₃-Ta₂O₅ system, and determine their structure. Study the phase relationship of the BaCO₃-HfO₂-MnCO₃ system. Synthesized a new solid solutions BaHfxMn_1-xO₃ (0.218; 0.145≤x≤0.165), their space group is P63/mmc, and the magnetization Ba₅Mn_4.25Hf_0.75O₁₅ and Ba₄Mn_3.128Hf_0.872O₁₅ have been showed paramagnetism in the room temperature and ferromagnetism in the 2K.