The role of orbital ordering in the tetragonal-to-cubic phase transition in CuCr2O4

Copper(II) chromite (CuCr2O4) undergoes a first-order structural transition from a tetragonal distorted spinel structure in space group (I41/amd) to a cubic spinel structure in Fd3¯m, near 600 °C. The transition has been followed using synchrotron X-ray powder diffraction between room temperature and 750 °C. The structure changes as a consequence of a transition from an orbitally ordered to orbital disordered state associated with a Jahn–Teller-type distortion of the CuO4 tetrahedron. The orbital melting results in a small increase in cell volume.

The first-order tetragonal–cubic phase transition in CuCr2O4 is accompanied by a noticeably reduction in cell volume associated with the loss of orbital ordering present in the low-temperature Jahn–Teller distorted tetragonal structure.Figure optionsDownload as PowerPoint slide