A New High-Pressure High-Temperature Phase of Silver Antimonate AgSbO₃ with Strong Ag–O Hybridization

We report on a new polymorph of silver antimonate AgSbO₃ discovered with the use of high-pressure high-temperature synthesis at 16 GPa and 1380 °C. The crystal structure is determined from X-ray powder diffraction, and we find this new high-pressure phase crystallizes in monoclinic space group <i>C</i>2/<i>c</i> with the following values: <i>a</i> = 8.4570(3) Å, <i>b</i> = 9.8752(3) Å, <i>c</i> = 8.9291(3) Å, β = 91.1750(12)°, and <i>V</i> = 745.56(4) ų. We synthesized the high-pressure (16 GPa) AgSbO₃ phase from the ilmenite phase as a precursor. This high-pressure monoclinic AgSbO₃ consists of a three-dimensional network of corner- and edge-sharing SbO₆ octahedra with channels along the <i>c</i>-direction containing Ag atoms. We also synthesize AgSbO₃ in the defect pyrochlore phase at 4 GPa from the same ilmenite precursor and compare the Raman spectra and the cation-anion bonding of all three AgSbO₃ phases. The absence of a cubic perovskite form of AgSbO₃ even at pressures of ≤16 GPa is likely due to the covalency of the Sb-O bonds and the moderate electronegativity of Ag⁺. Hybridization of Ag d and O p orbitals results in a variation of Ag-O distances that correlates with the band gap, which is in qualitative agreement with the density of states around the Fermi level from our density functional calculations. We compare AgSbO₃ with other ABX₃ compounds to elucidate the dependence of the structure on the constituent atoms.