The Effect of Cr-Doping on the Structure, Dielectric and Magnetic Properties of BiFeO_3 and Pb(Fe_(0.5)Sb_(0.5))O_3 Multiferroics

摘要

X-ray diffraction and M?ssbauer studies of perovskite BiFe_(1-x)Cr_(xO3) and PbFe_(0.5-x)Cr_xSb_0._5O_3 solid solution ceramics, fabricated under high pressure (4-6 GPa) have been carried out. Two morphotropic phase boundaries were revealed in the BiFe1-xCrxO3 system: one between rhombohedral (R3c) and orthorhombic (Pham) phases at x ≈ 0.5-0.6 and the other between the orthorhombic (Pbam) and monoclinic (C2/c) phases at x ≈ 0.9. It was found out that substitution of Cr~(3+) for Fe~(3+) in BiFeO_3 does not lead to the appearance of a low-spin state of Fe~(3+) ions, as was predicted by some first-principles calculations. A composition dependence of the magnetic phase transition temperature for BiFe_(1-x)Cr_(xO3) is very similar to that in the solid solutions of BiFeO_3 with non-magnetic ions, implying the lack of magnetic exchange between Fe~(3+) and Cr~(3+). The reason of such behavior seems to be a difference in their electronic configuration. Addition of Cr to PbFe_(0.5)Sb_(0.5)O_3 leads to a dramatic lowering and diffusion of the dielectric permittivity maximum and its shift to lower temperatures. Thus, Cr substitution for Fe seems to destroy both ferroelectric and magnetic long-range order in perovskite multiferroics.