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 $R{\mathrm{NiO}}_3$ $(R=\mathrm{lanthanide})$ 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 ${\mathrm{NdNiO}}_3$ and ${\mathrm{PrNiO}}_3$ suggests cooperative bond-length fluctuations in this region.

• Received 11 November 2002

DOI:https://doi.org/10.1103/PhysRevB.67.020404