Turnbull, R., Sánchez-Martín, J., Oliva, R., Ibáñez, J., Popescu, C., Rodríguez-Hernández, P., Muñoz, A., Nénert, G., Vie, D., & Errandonea, D. (2023). High-pressure evolution of silver iodate (AgIO3) and the γ−AgIO3 phase. Physical Review Materials, 7(8), 84606. https://doi.org/10.1103/PhysRevMaterials.7.084606
A phase of silver iodate, γ−AgIO3, has been obtained at ambient temperature by compressing α−AgIO3 to 1.60(5) GPa. The γ−AgIO3 crystal structure was identified via Rietveld refinement of high-pressure powder synchrotron x-ray diffraction. The γ−AgIO3 reflections were indexed to an orthorhombic lattice (Pbca) with unit-cell dimensions of a=7.2945(12), b=15.0013(24), c=5.3904(9)Å, and V=589.85(29)Å3 at 2.20(5) GPa. Density-functional theory calculations predict that γ−AgIO3 is more stable than α−AgIO3 above 0.15 GPa. The α→γ-phase transition is characterized by a decrease in the volume per formula unit of approximately 2% and it is reversible on decompression. Single-crystal optical-absorption measurements and density-functional theory calculations reveal the electronic band gap to decrease monotonically with increasing pressure in both α and γ phases, however the α→γ-phase transition (indirect → indirect) is characterized by an abrupt band-gap energy increase of approximately +0.18eV. This pressure induced band-gap evolution is rationalized based on the I-O bond lengths. The γ phase may correspond to an intermediate step between the previously known α and β phases.