Controlled Jahn-Teller distortion in (MgCoNiCuZn)O-based high entropy oxides

The influence of the synthesis conditions, stoichiometry and post-annealing treatments on the crystal structure of (MgCoNiCuZn)O-based high-entropy oxides have been investigated in details. The particular role of copper in the emergence of a distortion and a disordering of the randomly-distributed rocksalt structure has been evidenced by electron paramagnetic resonance and X-ray diffraction studies. An evolution of the local environment of copper from octahedral in Cu-sub-stoichiometric samples to rhombic in Cu-enriched samples leads to a deviation of the crystal structure from the ideal rocksalt one, which depends on the thermal history of the samples. Besides giving new clues to understand the behavior of this new class of materials, this controllable evolution of the crystal structure offers new possibilities of tuning the functional properties of the (MgCoNiCuZn)O-based compounds.