Structural transitions in Cu2O at pressures up to 11 GPa

The structural states of Cu2O at pressures between ambient and 11 GPa were re-investigated, using angle-dispersive diffraction, an area detector and synchrotron radiation. Thanks to the latter's naturally high collimation, a hitherto suspected transition from the parent cubic phase to a new tetragonal phase was experimentally confirmed at pressures between 0.7 and 2.2 GPa, depending on the hydrostaticity of the pressure medium used. The other transformation, into a pseudocubic phase, was detected at about 8.5 GPa. In the same pressure range, the application of pressure also resulted in a general and strong broadening of the diffraction peaks. This broadening is attributed to the presence of microscopic strains and a reduction in grain size down to the nanocrystalline scale.