Temperature-Induced Phase Transition in Cu₄TiSe₄

The newly synthesized ultralow thermal conducting Cu4TiSe4 undergoes a temperature-induced reversible structural phase transition at -92 degrees C. The room temperature structure exhibits cubic symmetry (space group P4? 3 m with lattice parameter a=5.6458(1) angstrom) and shows positional disorder in two Cu-sites (4e and 1a Wyckoff sites). In this report, a structural study was carried out on the same sample by means of single-crystal X-ray diffraction data (nitrogen-cryostat) collected at 131 K. At this temperature, Cu4TiSe4 crystallizes in rhombohedral symmetry, space group R3 m, with a=7.9538(5) angstrom and c=19.4828(17) angstrom. The low temperature structure is fourfold twinned. In the low temperature phase, copper atoms at 9b and 3a Wyckoff sites (originally 4e and 1a Wyckoff sites in the room temperature structure) order partially in comparison to room temperature structure. This temperature induced phase transition induce slight increase of the thermal conductivity of the material.