Synthetic Approach of Ternary Magnesium Niobate(Mg–Nb–O) Compounds

Magnesium based niobium oxides (Mg–Nb–O) were prepared by solid–state reactions owing to understand the function of transition metal oxides as promoters/catalysts for practical application. Magnesium niobate (Mg 3 Nb 6 O 11 ) was synthesized for the first time in nearly pure form reported in this context. MgNb 2 O 6 and Mg 4 Nb 2 O 9 were prepared in oxidizing conditions; on the contrary, Mg 3 Nb 6 O 11 preferred reducing environment. Stoichiometric mixtures of the precursor materials MgO, Nb 2 O 5 and/or metallic Nb were annealed for the syntheses which revealed the effect of temperature on phase formation, reaction kinetics and heat of reaction. The products were examined by ex–situ, in–situ X–ray diffraction (XRD) and differential scanning calorimetry (DSC). Crystallographic parameters of various binary and ternary compounds (Mg/Nb/O) formed in different calcination conditions, were extracted by Rietveld method. In–situ experiment results in single step reaction for the MgNb 2 O 6 synthesis and the heat of formation of the solid–state reaction obtained to be minimum (93 kJ/mol). In contrast, the formation of Mg 4 Nb 2 O 9 and Mg 3 Nb 6 O 11 compounds towards pure phases rather complicated due to multistep reactions and corresponding heat of formation were estimated to be 140 and 190 kJ/mol. Experimental results have been discussed based on kinetic and thermodynamic constrains.