Off-Stoichiometric NixCo3 – xO4 (x < 1) Spinels by Solution-Combustion Synthesis Using Citric Acid–Glycine Mixtures as a Dual Fuel

Solution-combustion synthesis of NixCo3 – xO4 (x < 1) spinels from aqueous solutions of nickel and cobalt nitrates using citric acid–glycine mixtures as a dual fuel was investigated by XRD and SEM. A decrease in combustion temperature at minimal amounts of glycine (φgl = 0.5) and citric acid (φcitr = 0.2–0.3) afforded for the synthesis of NiCo2O4 spinel after heat treatment of as-synthesized powders at 400°C for 20 h. An increase in the fuel content of starting solutions (for Σφ = φgl + φgl > 0.9) led to an increase in reaction temperature and the formation (after annealing at 400°C) of non-stoichiometric spinels NixCo3 – xO4 (x < 1) with an admixture of double oxides NiyCo1 – yO (y = 0.71–0.77).