Synthesis and crystallization of (Co, Cr, Fe, Mn, Ni)3O4 high entropy oxide: The role of fuel and fuel-to-oxidizer ratio

Abstract

The main object of this study is to synthesize (Co, Cr, Fe, Mn, Ni)3O4 high-entropy oxide through the solution combustion synthesis (SCS) method in the presence of different fuels at various fuel-to-oxidizer (F/O) ratios. Differential thermal analysis (DTA) and in-situ high-temperature XRD (HT-XRD) results demonstrated the high degree of thermal stability of the synthesized powder up to 1100 ​°C. According to XRD results, the single-phase high-entropy oxide was crystallized at fuel-lean conditions without any heat treatment. However, the single-phase high-entropy oxide was crystallized in all samples when they were heat-treated at 600 ​°C. X-ray photoemission spectroscopy (XPS) analysis and elemental-mapping analysis results clarified the high homogeneity of the obtained powder. Statistical analysis of results revealed a direct correlation of F/O, crystallinity, crystallite size, and lattice distortion values with magnetization saturation (Ms). Besides, the data represent an indirect correlation between micro-strain and Ms. The highest amount of Ms (14.6 emu/g) was obtained for the synthesized sample with a lattice distortion of 10.28%. Moreover, a specific surface area (SBET) value of 121 ​m2/g was obtained. In summary, the results indicated the significant role of fuel type and F/O ratio in improving the physicochemical properties of SCS synthesized (Co, Cr, Fe, Mn, Ni)3O4 high-entropy oxide.