Structure, phase diagram and magnetic properties of Bi1−xLaxFeO3 solid solution

Abstract

A series of polycrystalline Bi1−xLaxFeO3 (0≤x≤1.00) solid solution were synthesized by sol–gel method. The effects of lanthanum concentration on the phase formation, phase transition and magnetic properties were studied. The XRD results displayed that there is a clear indication of structural modification and symmetry change brought about by La doping. At room temperature the crystal structure of the solid solution transforms from rhombohedral R3c (x≤0.15) to tetragonal P4mm (0.15<x<0.40), then to cubic Pm3¯m (0.40≤x<0.50), and finally to orthorhombic Pbnm (0.50≤x≤1.00). In situ high temperature X-ray powder diffraction studies reveal that phase transformations of the rhombohedral R3c and the cubic Pm3¯m to the orthorhombic Pbnm occur in the temperature regions of 680–730°C and 300–680°C,respectively. The phase transformations of the tetragonal P4mm to the cubic Pm3¯m occurs in the temperature region of 200–230°C, whereas the phase structure of orthorhombic Pbnm keeps unchanged below 850°C. Based on careful characterization of crystal structure and phase transition as a function of temperature, the phase diagram of the pseudo-binary BiFeO3–LaFeO3 system has been constructed. The phase diagram manifests that the Bi1−xLaxFeO3 (0≤x≤1.00) solid solution provides more options to tune the magnetism and multiferroism, as the crystal structures with polarity feature occur in a wide doping concentration of La (x≤0.30). We then selectively studied the magnetic properties of possible multiferroic phases, i.e. R3c and P4mm phases. The results revealed that both the magnetic remanence and the coercive field of Bi1−xLaxFeO3 (0<x≤0.30) increased with the La content.