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Phase transition in Pr0.5Ca0.5CoO3 and related cobaltites

  • J. Hejtmánek
  • Z. Jirák
  • O. Kaman
  • K. Knížek
  • E. Šantavá
  • K. Nitta
  • T. Naito
  • H. Fujishiro
Regular Article
Part of the following topical collections:
  1. Topical issue: New Trends in Magnetism and Magnetic Materials

Abstract

We present an extensive investigation (magnetic, electric and thermal measurements and X-ray absorption spectroscopy) of the Pr0.5Ca0.5CoO3 and (Pr1−y Y y )0.7Ca0.3CoO3 (y = 0.0625 − 0.15) perovskites, in which a peculiar metal-insulator (M-I) transition, accompanied with pronounced structural and magnetic anomalies, occurs at 76 K and 40 − 132 K, respectively. The inspection of the M-I transition using the XANES data of Pr-L 3-edge and Co-K-edge proofs the presence of Pr4+ ions at low temperatures and indicates simultaneously the intermediate spin to low spin crossover of Co species on lowering the temperature. The study thus definitively confirms the synchronicity of the electron transfer between Pr3+ ions and Co3+/4+O3 subsystem and the transition to the low-spin, less electrically conducting phase. The large extent of the transfer is evidenced by the good quantitative agreement of the determined amount of the Pr4+ species, obtained either from the temperature dependence of the XANES spectra or via integration of the magnetic entropy change over the Pr4+ related Schottky peak in the low-temperature specific heat. These results show that the average valence of Pr3+/Pr4+ ions increases (in concomitance with the decrease of the formal Co valence) below T MI for (Pr0.925Y0.075)0.7Ca0.3CoO3 up to 3.16+  (the doping level of the CoO3 subsystem decreases from 3.30+  to 3.20+), for (Pr0.85Y0.15)0.7Ca0.3CoO3 up to 3.28+ (the decrease of doping level from 3.30+ to 3.13+) and for Pr0.5Ca0.5CoO3 up to 3.46+ (the decrease of doping level from 3.50+ to 3.27+).

Keywords

Doping Level Spectral Weight XANES Spectrum Magnetic Entropy Change Oxygen Stoichiometry 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  • J. Hejtmánek
    • 1
  • Z. Jirák
    • 1
  • O. Kaman
    • 1
  • K. Knížek
    • 1
  • E. Šantavá
    • 1
  • K. Nitta
    • 2
  • T. Naito
    • 3
  • H. Fujishiro
    • 3
  1. 1.Institute of Physics, ASCRPrague 6Czech Republic
  2. 2.Japan Synchrotron Radiation Research Institute, SayoHyogoJapan
  3. 3.Faculty of Engineering, Iwate UniversityMoriokaJapan

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