The Effects Of Y And La Doping On Structure And Multiferroic Properties Of BiFeO₃

The researches reveal there are a few materials that simultaneously have ferroelectric and ferromagnetic in normal temperature. BiFeO₃ is one of them. The Curie temperature Tc of BiFeO₃ is 830℃which means that when the temperature is higher than that, iron phase of BiFeO₃ will tansform from ferroelectric to para-electric. The antiferromagnetic transformation temperature which can also be named Néel temperature (TN) is 370℃. Curie temperature Tc and Néel temperature (TN) are way higher than the room temperature. The couple of the ferroelectric and ferromagnetic show us the view that electric field can adjust intrinsic magnetism and vice versa. Therefore, multiferroic materials are offer a choice of potential applications in sensors, spintronic devises and multiple-state memories. But they have intrinsic disadvantage for using them, for example they are very tough to be made in single phase which lead to a serious leaking current and BiFeO₃ has G type antiferromagnetic phase. But it is a canted G type phase which means the magnetism of adjacent atom is slightly canted and not antiparallel. This lead to no ferromagnetism due to the incommensurate cycloid spin structure. The researches show that oxygen hole existed in multiferroic materials lead to the high leakage and weak electric polarization. For overcoming these advantage, abundant research reveal that the rare earth element for A-site substitution to change the magnetoelectric properties of BiFeO₃ is the effective mathod.So in this article, we also use A-site substitution to change the properties of BiFeO₃. We obtain the crystal structure,ferroelectric hysteresis loop,ferromagnetic hysteresis loop and dielectric constant verse the change of frequency etc to analyze how the doping of different ratio and atom influent the properties of multiferroic materials. It has the following part:First, we synthesis the sample of Bi_1-xY_xFeO₃ ceramic materials through rapid liquid phase sintering method and the ratio of the x is 0.1,0.15 and 0.2. Through XRD and other test we can research the Y-substitution influence on the structure and multiferroic properties of BiFeO₃. when the doping ratio is 0.2, it will show possible transition of the structure from a rhombohedral phase to an orthorhombic phase. As the doping ratio of Y increases the weak ferromagnetism is gradually increased. The reason for this increasing of magnetism is that Y doped BFO will restrain the the incommensurate cycloid spin structure and make the magnetic structure show YFeO₃'s character.Second, we use the same method to produce the Y and La co-doped materials of Bi_0.9La_0.1-xY_xFeO₃(x=0, 0.05,0.08)samples. We can prevent the production of the second phase through co-doped effect and make the oxygen hole number less than the single doped materials that lead to the small leaking current and enhance the ferroelectric capability. The magnetic capability is still better for the Y element is also presented.Third, we use rapid liquid phase sintering method to produce Bi_0.9-xLa_0.1Y_xFeO₃(x=0,0.05,0.1) samples.Then compare them with Bi0.9-xLa0.1HoxFeO₃ sample. Because Y³⁺ ion has no magnetism, so it can prove the small ion Y can inhibit G type antiferromagnetic phase and increase the magnetism. The doped La ion can stable the BFO phase and inhibit other phases.