Thermal Behaviour of Sm(0.5)R(0.5)FeO(3) (R = Pr, Nd) Probed by High-Resolution X-ray Synchrotron Powder Diffraction

Mixed ferrites Sm(0.5)Pr(0.5)FeO(3) and Sm(0.5)Nd(0.5)FeO(3) with orthorhombic perovskite structure isotypic with GdFeO(3) 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 SmFeO(3)–PrFeO(3) and SmFeO(3)–NdFeO(3) pseudo-binary systems. Sm(0.5)Pr(0.5)FeO(3) and Sm(0.5)Nd(0.5)FeO(3) 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(0.5)Pr(0.5)FeO(3) and Sm(0.5)Nd(0.5)FeO(3) 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 RFeO(3) compounds. Subtle anomalies in the lattice expansion of Sm(0.5)Pr(0.5)FeO(3) and Sm(0.5)Nd(0.5)FeO(3) detected at 650–750 K reflect magnetoelastic coupling at the magnetic ordering temperature T(N).