Valence transition in (Pr,Ca)CoO3 cobaltites: Charge migration at the metal-insulator transition

Abstract

X-ray absorption spectroscopy measurements in Pr0.5Ca 0.5CoO3 and (Pr,Y)0.55Ca0.45CoO 3 compositions reveal that the valence of praseodymium ions is stable and essentially +3 (Pr [4f2]) in the metallic state, but abruptly changes when carriers localize approaching the oxidation state +4 (Pr [4f1]). This mechanism appears to be the driving force of the metal-insulator transition. The ground insulating state of Pr0.5Ca0.5CoO3 is a homogeneous Co3.5-δ state stabilized by a charge transfer from Pr to Co sites: 12Pr3++Co3 .5→12Pr3+2δ+Co3.5 -δ, with 2δ 0.26e-. © 2011 American Physical Society.