Anionogenic mixed valency in KxBa1-xO 2-δ

Shivakumara Giriyapura, Baomin Zhang, Robert A. de Groot, Gilles A. de Wijs, Antonio Caretta, Paul H.M. van Loosdrecht, Winfried Kockelmann, Thomas T.M. Palstra, Graeme R. Blake*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)


We have synthesized members of an isostructural solid solution series KxBa1-xO2-δ (x < 0.41, δ < 0.11) containing mixed-valent dioxygen anions. Synthesis in liquid ammonia solution allows a continuous range of compounds to be prepared. X-ray and neutron diffraction show that KxBa1-xO2-δ adopts the tetragonal rocksalt-derived structure of the end members KO 2 and BaO2, without any structural phase transition down to 5 K, the lowest temperature studied here. We identify four oxygen-oxygen stretching modes above 750 cm-1 in the measured Raman spectra, unlike the spectra of KO2 and BaO2 which both contain just a single mode. We use density functional theory calculations to show that the stretching modes in KxBa1-xO2-δ arise from in-phase and anti-phase coupling of the stretching of nearest-neighbor oxygen dimers when the valence state of the dimers lies between -1 and -2 because of mixed cation coordination. This coupling is a direct signature of a novel type of anionogenic mixed valency.

Original languageEnglish
Pages (from-to)496-502
Number of pages7
JournalInorganic chemistry
Issue number1
Publication statusPublished - 6 Jan 2014
Externally publishedYes


  • Inelastic neutron-scattering
  • Onitio molecular-dynamics
  • Augmented-wave method
  • Hyperoxides
  • Systems
  • Magnetogyration
  • Ferromagnetism
  • Spectroscopy
  • Peroxides
  • Graphite
  • n/a OA procedure


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