Crystalline electric field of the rare-earth nickelates RNiO3 (R = Pr, Nd,Sm, Eu, and Pr1-xLax, 0 <= x <= 0.7) determined by inelastic neutron scattering

The rue-earth based nickelates RNiO3 (R=Pr, Nd, Sm, Eu, and Pr1-xLax, 0 les s than or equal to x less than or equal to 0.7) were studied by inelastic n eutron scattering. Energy splittings due to the crystalline-electric-field (CEF) interaction at the R3+ site within the electronic ground-state J mult iplet (for R=Pr, Nd, and Pr1-xLax) as well as within the two lowest-lying J multiplets (for R = Sm and Eu) were directly: observed, and the correspond ing CEF energy-level schemes were reconstructed. The latter were rationaliz ed in terms of CEF parameters, which vary smoothly over: the rare-earth ser ies and give magnetic properties associated with the R sublattice in agreem ent with results from neutron powder diffraction experiments, Across the me tal-insulator transition, a continuous change in the electronic part of the CEF parameters is observed. However, an attempt to quantify a charge trans fer from the observed variation of the CEF parameters in an effective point charge model failed, probably due to the strong covalency in these compoun ds. Across the structural transition occurring in Pr1-xLaxNiO3 at x = 0.7, a change in the symmetry of the CEF ground state is observed, which has a p rofound influence on the thermodynamic properties. [S0163-1829(99)01145-5].