XRD study of U3O8 structure at different temperature

The structure change of triuranium octaoxide (U3O8) is studied by X-ray diffraction in ambient atmosphere at temperature from 25 degree C to 850 degree C. There are two kinds of phases of U3O8 in the temperature range, and the transformation temperature is about 300 degree C. The lower temperature phase is orthorhombic with space group Amm2, and it changes to another phase with better symmetry around 300 degree C. Another phase, the higher temperature phase, is hexagonal with space group P-62m, which is stable from 300 degree C to 800 degree C. The lattice parameters of XRD peaks of U3O8 are also investigated at different temperature. It is found that they change with the temperature under rules