Thermal Behaviour of Sm0.5 R 0.5FeO3 (R?=?Pr, Nd) Probed by High-Resolution X-ray Synchrotron Powder Diffraction

摘要

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 R FeO~(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).