Influence of Ni-Cu substitution and uneven element content on electrical properties of high entropy oxides

High entropy oxides (HEOs) are of great interest for heat conversion due to their promising electrical and thermal properties. In this research, we aim to obtain single-phase HEO with the chemical composition Co-Cr-Fe-Mn-Ni-O, with the unequal at. % of metals, via Solid-State Reaction (SSR), and substitute Ni with Cu. The samples were sintered at 1000 °C for 20 – 35 h. For the samples with Ni, two main phases were formed: rock salt-structured Fm-3m and spinel-structured Fd-3m. As for the material with Cu, single-phase material was formed with the spinel-crystal structure Fd-3m. Obtained samples exhibit high values of the Seebeck coefficient (330 μV/K at 573 K for the sample with Ni that was synthesized for 35 h and 120 μV/K at 573 K for the sample with Cu) and electrical conductivity (4.58 S/cm at 1073 K for the single-phased sample with Cu). These results indicate that these materials can be used as highly efficient semiconductor high-entropy alloys. Further optimization of the SSR is needed to produce a single-phase material with Ni.