Comparative study of ultrafast high-temperature sintering (UHS) configurations for accelerated synthesis of (MgCoNiCuZn)O high-entropy oxide

Ultrafast high-temperature sintering (UHS) was employed to synthesize (MgCoNiCuZn)O in just 60 s using three different heating configurations: Standard with direct graphite felt contact (S-UHS), Alumina-separated (A-UHS), and Non-Contact (NC-UHS). All samples developed the targeted rock-salt phase, though their density, oxygen retention, and chemical uniformity varied with the UHS configuration. The NC-UHS required higher electrical power to reach comparable temperatures and showed the most pronounced oxygen loss, consistent with stronger carbon-assisted reduction conditions near the felt. The A-UHS demonstrated the highest uniformity and oxygen retention due to minimized contact with carbon. For comparison, S-UHS achieved the highest density but showed partial surface reduction. Surface impurities followed a trend of S-UHS < A-UHS < NC-UHS. These results suggest that the thermal and chemical contact during UHS significantly impacts heating efficiency, redox processes, and phase purity, enabling reproducible synthesis of high-entropy oxides.