Temperature-dependent Structural and Spectroscopic Studies of (Bi1–xFex)FeO3

We report on temperature-dependent structural and spectroscopic features of (Bi1–xFex)­FeO3 perovskite for x = 0.15 and 0.25. Samples were synthesized by heating quantum crystalline precursors obtained by the polyol method. Crystal structures of each composition were obtained from in-house X-ray, synchrotron X-ray, and time-of-flight neutron powder diffraction data Rietveld refinements. Partial replacement of the Bi site by the Fe3+ cation significantly changes the crystal physicochemical properties, such as thermal expansion, polyhedral distortion, Debye temperature, and vibrational and magnetic properties. Whereas BiFeO3 is multiferroic, both Bi0.85Fe0.15FeO3 and Bi0.75Fe0.25FeO3 are found to be superparamagnetic, as observed by temperature-dependent Mössbauer and SQUID measurements. Lattice thermal expansion was modeled using the Debye–Einstein-anharmonicity approach. Debye temperatures obtained from the mean-squared atomic displacement parameter and lattice thermal expansion are compared. Temperature dependence of selective Raman modes is also analyzed.