Possible common ground for the metal-insulator phase transition in the rare-earth nickelatesRNiO3(R=Eu,Ho, Y)

Abstract

We report on the infrared spectra of $R{\mathrm{NiO}}_{3}$ $(R=\mathrm{Eu},$ Ho, Y). They provide evidence of phonon and insulating gap behavior and point to the monoclinic distortion at the metal-insulator (MI) transition as a feature for all $R{\mathrm{NiO}}_{3}$ $(R\ensuremath{\ne}\mathrm{La}).$ We hypothesize that the intermediate paramagnetic phase (above ${T}_{N}$ and below ${T}_{\mathrm{MI}})$ in $R{\mathrm{NiO}}_{3}$ $(R=\mathrm{Sm},$ Eu, Ho, Y) might be consequence of a self-doping effect, gradually triggering a phase segregation in electron-rich and electron-poor regions. This picture is concomitant to the temperature-dependent effect of octahedral tilting and distortion and self-trapped electrons in a polaronic medium.