Evidence for electron-lattice coupling in RNiO3 perovskites

In order to get additional insight into the origin of the metal-insulator transition in RNiO3 perovskites we have investigated (a) the stability of the magnetic structure against the proximity of the metallic state and (b) the effect of the oxygen isotope mass on the metal-insulator transition temperature T-MI. The observation of the same kind of magnetic 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 well as the unusually large, rare-earth-dependent O-16-O-18 isotope shift 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 Science B.V. All rights reserved.