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Antimony oxides are important materials for catalysis and flame-retardant applications. The two most common phases, α-Sb₂O₃ (senarmontite) and β-Sb₂O₃ (valentinite), have been studied extensively. Specific focus has been placed recently on their lattice dynamics properties and how they relate to the α-β 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. α-Sb₂O₃ behaved as expected, but β-Sb₂O₃ revealed a small region of zero thermal expansion along the c axis. Additionally, while the β phase matched well with reported atomic displacement parameters, the α phase displayed a marked deviation. This data will enable further investigations into these systems.