Crystal structure, chemical expansion and phase stability of HoMnO3 at high temperature

► Thermal evolution of crystal structure of HoMnO3 studied up to 1623 K in air and N2. ► Anisotropic chemical expansion of HoMnO3 and YMnO3 in N2, air and O2. ► Hexagonal phase destabilized with respect to perovskite in oxidizing atmosphere. ► Crystal structure and phase stability discussed in terms of point defect chemistry. ► Electrical conductivity anomalies associated with excess oxygen at 550-630 K.