Vibrations and Phase Stability in Mixed Valence Antimony Oxide.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Computational Materials Science

Background:

• Antimony tetroxide exists in alpha (cervantite) and beta (clinocervantite) phases, both mixed valence compounds (SbIII SbV O4).
• The presence of SbIII lone-pair electrons complicates theoretical calculations of their structure and properties.

Purpose of the Study:

• To investigate the lattice dynamics and vibrational properties of alpha- and beta-antimony tetroxide.
• To understand the factors governing the phase stability of antimony tetroxide, particularly the alpha phase.
• To explore the influence of oxygen vacancies on the stoichiometry and properties of these compounds.

Main Methods:

• Inelastic neutron scattering (INS)
• Mössbauer spectroscopy
• Nuclear inelastic scattering (NIS)
• Density functional theory (DFT) calculations, including those accounting for lone-pair electrons and oxygen vacancies.

Main Results:

• DFT calculations incorporating lone-pair electrons accurately reproduced experimental phonon state densities.
• Mössbauer spectroscopy indicated that the beta phase is considerably harder than the alpha phase.
• Calculations suggested that oxygen vacancies allow for nonstoichiometric SbIII/SbV ratios in both phases.
• Vibrational entropy differences were found to be small, making them unlikely drivers for alpha phase stability.

Conclusions:

• The stability of the alpha phase over the beta phase is likely due to nonstoichiometry rather than vibrational entropy.
• The findings provide insights into the complex behavior of mixed valence antimony oxides and the role of defects.