Structural phase transition and thermal expansion in Bi1−2.5 x Pr1.5 x Ba x FeO3 ceramics.

The temperature dependence of the crystal structure for Bi1−2.5 x Pr1.5 x Ba x FeO3 (x =0.05, 0.1) polycrystallines is studied by X-ray powder diffraction with Rietveld refinements in the temperature range of 25–800°C. A structural phase transition of Rhombohedral-to-Cubic occurs for Bi0.875Pr0.075Ba0.05FeO3 sample in the temperature of 600–700°C, which may relate to its unstable rhombohedra distorted structure with the space group R3c. The rarely decomposition of these samples indicates that the Pr, Ba co-doped make the BiFeO3 ceramics more stable. The thermal expansion determined by the temperature dependence of the unit-cell lattice parameters and volumes for Bi1−2.5 x Pr1.5 x Ba x FeO3 samples is also investigated, which shows an isotropic and positive behavior. The average thermal expansion coefficient decreases with the increasing x. We argue that the Cubic crystal structure with the high symmetrical of the space group Pm3m may be more stable for Bi0.75Pr0.15Ba0.1FeO3 sample, which may explain the reason why no phase transition occurs and its lower thermal expansion efficiencies. An obvious change in the slope of the linear fitted lines between 300°C and 400°C suggests a possible antiferromagnetic–paramagnetic transition, which occurs around the Néel temperature of the Bi1−2.5 x Pr1.5 x Ba x FeO3 samples. [ABSTRACT FROM AUTHOR]