Transition from Curie-Weiss to enhanced Pauli paramagnetism in RNiO3 (R = La,Pr,...Gd)

High-oxygen-pressure annealing, cold pressing, and measurement of properties under pressure have been used to reveal and to follow in the single-valent perovskites RNiO3 (R=lanthanide) a crossover from localized to itinerant electronic behavior. Cold pressing proved critical for obtaining nearly intrinsic transport properties such as electronic and thermal conductivity in polycrystalline samples not available as single crystals. Suppression of the thermal conductivity in the crossover compositions NdNiO3 and PrNiO3 suggests cooperative bond-length fluctuations in this region.