Defect structure and transport properties of (Co,Cr,Fe,Mn,Ni)3O4 spinel-structured high entropy oxide

Defect structure and chemical diffusion in the (Co,Cr,Fe,Mn,Ni)3O4 high entropy oxide is investigated. The material is synthesized by means of a solid-state reaction, through sintering mixture of composing oxides at 1273 K for 20 h. Presence of the single-phase, spinel-structured high entropy solid solution is confirmed with the use of X-ray diffraction method and scanning electron microscopy. Good thermal stability of the material is documented up to 1273 K. Modified marker experiment allows concluding that defects form predominantly in the oxygen sublattice. Based on thermogravimetric studies, general formula of (Co,Cr,Fe,Mn,Ni)3O4±y is established, with the defect inversion phenomenon (i.e. change of the dominating type of defects from oxygen vacancies to interstitial oxygen) likely to occur at high oxygen partial pressures (pO2). Chemical diffusion coefficient is calculated, based on the measured reequilibration kinetics, showing a very strong dependence on pO2 and relatively small values under low oxygen pressures.