Co-Cr-Fe-Mn-Ni Oxide as a Highly Efficient Thermoelectric High-Entropy Alloy

Among the existing materials for heat conversion, high-entropy alloys are of great interest due to the tunability of their functional properties. Here, we aim to produce single-phase high-entropy oxides composed of Co-Cr-Fe-Mn-Ni-O through spark plasma sintering (SPS), testing their thermoelectric (TE) properties. This material was successfully obtained before via a different technique, which requires a very long processing time. Hence, the main target of this work is to apply spark plasma sintering, a much faster and scalable process. The samples were sintered in the temperature range of 1200-1300 degrees C. Two main phases were formed: rock salt-structured Fm (3) over barm and spinel-structured Fd (3) over barm. Comparable transport properties were achieved via the new approach: the highest value of the Seebeck coefficient reached -112.6 mu V/K at room temperature, compared to -150 mu V/K reported before; electrical properties at high temperatures are close to the properties of the single-phase material (sigma = 0.2148 S/cm, sigma approximate to 0.2009 S/cm reported before). These results indicate that SPS can be successfully applied to produce highly efficient TE high-entropy alloys in a fast and scalable way. Further optimization is needed for the production of single-phase materials, which are expected to exhibit an even better TE functionality.