Structure and Anharmonicity of - and -Sb₂O₃ at Low Temperature

Antimony oxides are important materials for catalysis and flame-retardant applications. The two most common phases, alpha-Sb2O3 (senarmontite) and beta-Sb2O3 (valentinite), have been studied extensively. Specific focus has been placed recently on their lattice dynamics properties and how they relate to the alpha-beta phase transformation and their potential anharmonicity. However, there has not been any direct investigation of anharmonicity in these systems, and a surprising lack of low-temperature structural information has prevented further study. Here, we report the powder neutron diffraction data of both phases of Sb2O3, as well as structural information. alpha-Sb2O3 behaved as expected, but beta-Sb2O3 revealed a small region of zero thermal expansion along the c axis. Additionally, while the beta phase matched well with reported atomic displacement parameters, the alpha phase displayed a marked deviation. This data will enable further investigations into these systems.