Persistence of Mixed and Non-intermediate Valence in the High-Pressure Structure of Silver(I,III) Oxide, AgO: A Combined Raman, X-ray Diffraction (XRD), and Density Functional Theory (DFT) Study

Adam Grzelak; Jakub Gawraczyński; Tomasz Jaroń; Maddury Somayazulu; Mariana Derzsi; Viktor Struzhkin; Wojciech Grochala

doi:10.1021/acs.inorgchem.7b00405

Persistence of Mixed and Non-intermediate Valence in the High-Pressure Structure of Silver(I,III) Oxide, AgO: A Combined Raman, X-ray Diffraction (XRD), and Density Functional Theory (DFT) Study

Inorg Chem. 2017 May 15;56(10):5804-5812. doi: 10.1021/acs.inorgchem.7b00405. Epub 2017 May 2.

Authors

Adam Grzelak^{1

2}, Jakub Gawraczyński^{1

2}, Tomasz Jaroń^{2

3}, Maddury Somayazulu³, Mariana Derzsi², Viktor Struzhkin³, Wojciech Grochala²

Affiliations

¹ Faculty of Chemistry, University of Warsaw , ul. Pasteura 1, 02-093 Warsaw, Poland.
² Center of New Technologies, University of Warsaw , ul. Banacha 2C, 02-097 Warsaw, Poland.
³ Geophysical Laboratory, Carnegie Institution of Washington , 5251 Broad Branch Road NW, Washington, D.C. 20015, United States.

PMID: 28463489
DOI: 10.1021/acs.inorgchem.7b00405

Abstract

The X-ray diffraction data collected up to ca. 56 GPa and the Raman spectra measured up to 74.8 GPa for AgO, or Ag^IAg^IIIO₂, which is a prototypical mixed valence (disproportionated) oxide, indicate that two consecutive phase transitions occur: the first-order phase transition occurs between 16.1 GPa and 19.7 GPa, and a second-order phase transition occurs at ca. 40 GPa. All polymorphic forms host the square planar [Ag^IIIO₄] units typical of low-spin Ag^III. The disproportionated Imma form persists at least up to 74.8 GPa, as indicated by Raman spectra. Theoretical hybrid density functional theory (DFT) calculations show that the first-order transition is phonon-driven. AgO stubbornly remains disproportionated up to at least 100 GPa-in striking contrast to its copper analogue-and the fundamental band gap of AgO is ∼0.3 eV at this pressure and is weakly pressure-dependent. Metallization of AgO is yet to be achieved.