Rapid Synthesis and Detailed Characterization of Low-Dimensional Mixed-Valent Sr₆Rh₅O₁₅ Nanofibers: Theory and Experiments

We report the facile growth of one-dimensional strontium rhodium oxide (Sr₆Rh₅O₁₅) nanofibers with high crystallinity by utilizing an electrospinning process, followed by thermal annealing. The Sr₆Rh₅O₁₅ nanofibers retain their characteristic fibrous nanostructure with notably rough surface morphologies even after annealing at 900 °C, demonstrating outstanding structural durability at harsh temperatures. The crystal structure of the Sr₆Rh₅O₁₅ nanofibers was examined through X-ray diffraction patterns combined with Rietveld refinement, confirming the rhombohedral crystal structure belonging to the space group R32. X-ray photoelectron spectroscopy results indicate that some rhodium ions are in an oxidation state higher than that of Rh³⁺, suggesting that Rh cations in Sr₆Rh₅O₁₅ exist in mixed valence states of Rh⁴⁺ and Rh³⁺. Furthermore, micro-Raman scattering analysis elucidated the lattice mode dynamics in the Sr₆Rh₅O₁₅ nanofibers, showing that the overall features of the experimental Raman spectra qualitatively agree with density functional theory calculations. These findings enhance our understanding of the physicochemical properties of Sr₆Rh₅O₁₅ nanofibers and provide insights into potential real-world applications of this material.