EVIDENCE FOR ELECTRON-LATTICE COUPLING IN RNIO3 PEROVSKITES

In order to get additional insight into the origin of the metal-insula tor transition in RNiO3 perovskites we have investigated (a) the stabi lity of the magnetic structure against the proximity of the metallic s tate and (b) the effect of the oxygen isotope mass on the metal-insula tor transition temperature T-MI. The observation of the same kind of m agnetic ordering in the four nickelates studied (PrNiO3, NdNiO3 with T -MI = T-N, and (SmNiO3)-Sm-154, (EuNiO3)-Eu-153 with T-N < T-MI), as w ell as the unusually large, rare-earth-dependent O-16-O-18 isotope shi ft we found in these materials (Delta T-MI less than or equal to + 10. 3 K) strongly support the electron-lattice interaction as the driving force for the metal-insulator transition. The possibility of a dynamic to static Jahn-Teller transition is discussed. (C) 1998 Elsevier Scie nce B.V. All rights reserved.