Electron-phonon interactions in perovskites containing Fe and Cr studied by Raman scattering using oxygen-isotope and cation substitution

摘要: We use temperature-dependent inelastic light scattering to study the origin of strong multiphonon a local oxygen breathing mode present in mixed $B$-site orthorhombic (space group $Pnma$) perovskite ${\text{LaFe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$ but absent isostructural ${\text{LaFeO}}_{3}$ and ${\text{LaCrO}}_{3}$. It is seen that critically sensitive presence both Fe Cr ions on $B$ site. These results support our interpretation activated by electron-phonon interactions according Franck-Condon picture following an Fe-Cr charge transfer. Further, $^{18}\text{O}$ substitution performed $x=0$, 0.04, 0.5 compounds clearly shows all modes appearing above first-order phonon-scattering region these originate from higher-order stretching vibrations. In particular this case for second-order dominating response ${\text{LaFeO}}_{3}$. Accordingly we propose are generated infrared-active longitudinal optical (IR LO) two-phonon combination Fr\"ohlich interaction. For $x=0.02$ 0.04 characteristic IR LO multiphonon-scattering profiles mix. also influence isovalent cation Sr doping $A{\text{Fe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$ ($A=\text{La}$, Nd, Gd) ${\text{La}}_{1\ensuremath{-}y}{\text{Sr}}_{y}{\text{Fe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3\ensuremath{-}\ensuremath{\delta}}$ ($y=0$, 0.16, 0.5) coupling ${\text{LaFe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$. The effect ${\text{LaFe}}_{0.5}{\text{Cr}}_{0.5}{\text{O}}_{3}$, not significantly affected $A$-site substitution, despite increasing distortion associated with decreasing ionic radii. On contrary, aliovalent causes rapid decrease scattering. This highly lattice electronic decoherence insensitive global distortions. Finally, preliminary assignment ${A}_{g}$ ${B}_{2g}$ phonon made based observations published ${\text{LaCrO}}_{3}$ $A{\text{MnO}}_{3}$. octahedral tilt bending vibrations heavily influenced magnitude distortion.