Multiferroic Properties Of Y-doped BiFeO₃ Ceramics And Bi_0.9Y_0.1FeO₃-PbTiO₃ Ceramics

Bismuth ferrite, BiFeO₃, is one kind of important magnetoelectric material, which simultaneously exhibits ferroelectric ordering and antiferromagnetic ordering in the bulk form. It presents opportunities for potential applications in information storage, satellite communication, and magneto-electric sensors.In this thesis, Y-doped BiFeO₃ ceramics were firstly prepared by the conventional solid-state reaction. By X-ray diffraction the crystal structures of the samples were identified to be rhombohedral with R3c space group. A significant enhancement of magnetic properties was clearly observed in Y-doped BiFeO₃ ceramics though no improvement in the ferroelectric properties. The saturation magnetic values were 0.1440, 0.7468, 1.9217, 3.3309 and 6.2774 emu/g at 300K for x=0, 0.05, 0.10, 0.15 and 0.20, respectively.Moreover, the solid solutions of Bi_0.9Y_0.1FeO₃ with PbTiO₃ were prepared. It was clear that in Bi_0.9Y_0.1FeO₃-PbTiO₃ solid solution, the structure remined rhobohedral for 85 mole% of Bi_0.9Y_0.1FeO₃ , from 80 to 70 mole% it were rhobohedral and tetragonal, and below 65 mole%, the structure transformed to tetragonal. The dielectric and ferroelectric properties of the ceramics had been significantly improved by means of ionic substitution of Ti⁴⁺ for Fe³⁺, which reduced the electric conductivity. The dielectric constants of the ceramic samples were enhanced from 84 to 241 and the remnant polarizations were improved from 0.494 to 2.17μC/cm² .Finally, it was discussed for the mechanism of the samples transformed from antiferromagnetism to ferrimagnetism. The saturation magnetization values of Bi_1-xY_xFeO₃(x=0-0.20) were also calculated.