The Effects Of PR And HO Doping On Structure And Multiferroic Properties Of BiFeO₃

Multiferroics materials are the materials that exhibit both ferromagnetism and ferroelectricity, also presence a coupling between them. Because of its excellent property, it becomes a hot multifunctional material. In all of these materials, BiFeO₃ shows a high anti-ferromagnetic and ferroelectric orders temperature (TN=673K, Tc=1103K), made it likely to become to a widely used multiferroics materials at room temperature. However, due to its high leakage and weak ferromagnetism BiFeO₃ is unsuitable for applelication. Many investigations revealed that partial substitutions of rare-earth ions (e.g., La³⁺, Nd³⁺, or Sm³⁺) for bismuth help in eliminating the secondary phase along with a structural phase transition improving ferroelectric properties of BiFeO₃. The introduction of rare-earth cations in BiFeO₃ seems to increase the magnetocrystalline anisotropy, thus making the cycloidal spin structure energetically unfavorable.We have chosen two doping systems as subject of our research, Pr doped Bi_1-xPr_xFeO₃ system (x=0,0.05,0.1,0.15,0.2) and Ho doped sample Bi_0.85La_0.1Ho_0.05FeO₃, the main contents and results are as following:The doping materials were prepared through the rapid liquid phase sintering method. The X-ray diffraction patterns reveales a phase transition from rhombohedral structure to orthorhombic structure in Pr-doped system at x=0.2. The magnetic measurements showed that the substitution enhance the magnetic properties of BiFeO₃ effectively.The ferroelectric properties and leakagemeasurement of the samples were taken. The results reveales that doping can enhance the ferroelectric properties of Pr doped samples. Dielectric measurement shows that the dielectric constant (ε) increased while decreased the dielectric loss effectively along with the doping for Pr doped samples. And also the M-E effect are enhanced for Pr doping sampled.The ferroelectric properties of the Ho doped sample are also enhanced. The temperature dependence of dielectric constant(ε) curve shows a dielectric anomaly in the dielectric constant at 643K. It is believed that this is induced by the magnetoelectricity coupling. The coupling between electric and magnetic dipoles in La and Ho codoped samples has also been demonstrated by measuring the effect of magnetization on the ferroelectric hysteresis loop.