GiantO16−O18Isotope Effect on the Metal-Insulator Transition ofRNiO3Perovskites (R=Rare Earth)

The observation of unusually large, positive and rare-earth dependent ${}_{}{}^{16}{}_{}{}^{}O\mathrm{-}{}_{}{}^{18}{}_{}{}^{}O$ isotope shifts in the metal-insulator transition temperature $T_{\mathrm{MI}}$ of $R\mathrm{NIO}{}_3$ perovskites is reported $(\Delta T_{\mathrm{MI}}\le +10.3\mathrm{}\mathrm{K})$. The results clearly indicate that the mechanism of the transition involves a strong electron-lattice interaction. A simple model based on the existence of Jahn-Teller polarons in a stoichiometric, metallic, charge-transfer system is used to account for the evolution of $\Delta T_{\mathrm{MI}}$ along the series.