Mechanochemical Synthesis of (Co,Cu,Mg,Ni,Zn)O High-Entropy Oxide and Its Physicochemical Properties

The study describes the physicochemical properties of transition metal (Co,Cu,Mg,Ni,Zn)O high-entropy oxide prepared using mechanochemical synthesis (MS) followed by thermal treatment, as well as the structural evolutions in the powder with milling time. The microstructure and electrical properties of the materials were studied using x-ray diffraction, scanning electron microscopy—energy dispersive spectroscopy and electrochemical impedance spectroscopy. The powders obtained after 30 h and 100 h of MS contained a mixture of two phases with a rock salt structure and, in addition, about 11 wt.% of Co3O4. Sintering these materials for 10 h in air at 1273 K led to the formation of a single-phase, solid solution with a rock salt structure. The developed sinters exhibited a fine-crystalline structure of grains and a uniform distribution of elements. The highest electrical conductivity was measured at 1148 K, and it was equal to 8.03 × 10−2 S cm−1.