The phase transition in α-U₃O₈ at 210°C

The structure of α-U₃O₈ above the transition point at 210°C has been determined from neutron powder diffraction data. It was found to be very similar to the structure at room temperature. Contrary to experimental evidence, theory does not allow a second order phase transition from the structure at high temperature (space group P2m) to that at room temperature (space group C2mm).