Thermal Behaviour of Sm0.5R0.5FeO3 (R = Pr Nd) Probed by High-Resolution X-ray Synchrotron Powder Diffraction

摘要

Mixed ferrites Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO3 with orthorhombic perovskite structure isotypic with GdFeO3 were synthesized by solid-state reaction technique in air at 1473 K. Structural parameters obtained at room temperature prove a formation of continuous solid solutions in the SmFeO3–PrFeO3 and SmFeO3–NdFeO3 pseudo-binary systems. Sm0.5Pr0.5FeO3 and Sm0.5Nd0.5FeO₃ show strongly anisotropic nonlinear thermal expansion: thermal expansion in the b direction is twice lower than in the a and c directions. The average linear thermal expansion coefficients of Sm_0.5Pr_0.5FeO₃ and Sm_0.5Nd_0.5FeO₃ in the temperature range of 298–1173 K are in the limits of (9.0–11.1) × 10⁻⁶ K⁻¹, which is close to the values reported for the parent RFeO₃ compounds. Subtle anomalies in the lattice expansion of Sm_0.5Pr_0.5FeO₃ and Sm_0.5Nd_0.5FeO₃ detected at 650–750 K reflect magnetoelastic coupling at the magnetic ordering temperature T_N.