Valence transition in (Pr,Ca)CoO3 cobaltites: Charge migration at the metal-insulator transition
Abstract
6 páginas, 5 figuras, 1 tabla.-- PACS number(s): 71.30.+h, 75.25.Dk, 75.30.Wx, 78.70.Dm.-- et al. ; X-ray absorption spectroscopy measurements in Pr0.5Ca0.5CoO3 and (Pr,Y)0.55Ca0.45CoO3 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: 1/2Pr3++Co3.5→1/2Pr3+2δ+Co3.5-δ, with 2δ ≈ 0.26e-. ; Financial support from MICINN (Spanish government) under Projects No. MAT2006-11080-C02-02 and No. MAT2009-09308, and NANOSELECT under Project No. CSD2007-00041 is acknowledged. The ALICE diffractometer is funded through the BMBF under Contract No. 05KS7PC1. The research leading to these results has received funding from the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 226716 ; Peer reviewed
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