Structural, Mössbauer, and Optical studies of mechano-synthesized Ru3+-doped LaFeO3 nanoparticles

Single-phased Ru³⁺-doped LaFeO₃ nanocrystalline particles (6-70 nm), with nominal compositions of LaFe_1-xRu_xO₃ (x = 0.00, 0.015, 0.03, 0.05 and 0.08), were prepared using mechano-synthesis at temperatures that are ca. 400 °C- 700 °C lower than those used to synthesize cation-doped LaFeO₃ conventionally. The Ru³⁺ ions are found to substitute exclusively for the Fe³⁺ ones at the octahedral sites of the perovskite-related structure. The lattice parameters of all samples are suggestive of a weak Jahn-Teller-like distortion as opposed to the normal distortion of orthorhombic perovskites. ⁵⁷Fe Mössbauer measurements for all samples show the Fe³⁺ ions to be in high-spin state implying that the observed lattice distortion is due to particle-size surface-induced disorder rather than the electronic degeneracy associated with the normal Jahn-Teller distortion. The decrease in the Mössbauer hyperfine magnetic fields with increasing Ru³⁺ content is attributed mainly to particle size reduction rather than the cationic substitution of Fe³⁺ by the Ru³⁺. A monotonic decrease of the optical band gap from 2.17 eV (x = 0.00) to 1.79 eV (x = 0.08) was observed, revealing how doping with Ru³⁺ affects the optical absorption of the LaFeO₃ nanoparticles.