Simultaneous first-order valence and oxygen vacancy order/disorder transitions in (Pr0.85Y0.15)0.7Ca0.3CoO3-δ via analytical transmission electron microscopy

Ahmet Gulec, Daniel Phelan, Chris Leighton, Robert F. Klie

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

Perovskite cobaltites have been studied for years as some of the few solids to exhibit thermally driven spin-state crossovers. The unanticipated first-order spin and electronic transitions recently discovered in Pr-based cobaltites are notably different from these conventional crossovers, and are understood in terms of a unique valence transition. In essence, the Pr valence is thought to spontaneously shift from 3+ toward 4+ on cooling, driving subsequent transitions in Co valence and electronic/ magnetic properties. Here, we apply temperature-dependent transmission electron microscopy and spectroscopy to study this phenomenon, for the first time with atomic spatial resolution, in the prototypical (Pr0.85Y0.15)0.70 Ca0.30CoO3-δ. In addition to the direct spectroscopic observation of charge transfer between Pr and Co at the 165 K transition (on both the Pr and O edges), we also find a simultaneous order/disorder transition associated with O vacancies. Remarkably, the first-order valence change drives a transition between ordered and random O vacancies, at constant O vacancy density, demonstrating reversible crystallization of such vacancies even at cryogenic temperatures.

Original languageEnglish (US)
Pages (from-to)938-947
Number of pages10
JournalACS nano
Volume10
Issue number1
DOIs
StatePublished - Jan 26 2016

Keywords

  • Electron energy loss spectroscopy
  • Oxygen vacancy ordering
  • Perovskite cobaltites
  • Spin-state transitions
  • Transmission electron microscopy

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