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.