GIANT O-16-O-18 ISOTOPE EFFECT ON THE METAL-INSULATOR-TRANSITION OF RNIO3 PEROVSKITES (R EQUALS RARE-EARTH)

The observation of unusually large, positive and rare-earth dependent O-16-O-18 isotope shifts in the metal-insulator transition temperature T-MI Of RNIO3 perovskites is reported (Delta T-MI less than or equal to +10.3 K). The results clearly indicate that the mechanism of the tr ansition involves a strong electron-lattice interaction. A simple mode l 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-MI along the series.