Ammonium niobate oxalate hydrate

The metal oxide was prepared by the solution combustion technique which is considered a quick and efficient technique to yield nanoparticles with high phase purity.³⁷ A detailed procedure of preparing doped and pristine metal oxide by the solution combustion technique can be found elsewhere.^{29 (link)} Ammonium niobate oxalate hydrate (Sigma-Aldrich, USA) was used as the precursor for niobium and urea as the fuel. All other chemicals used were of analytical grade. To prepare Nb₂O₅, initially, the niobium precursor and urea were dissolved in DI water separately via sonication for 10 min and later mixed together. The mixed clear solution was kept in a preheated muffle furnace at 450 °C for 30 min. Black Nb₂O₅ was obtained.^{38 (link)} This catalyst was then calcined at 550 °C for 4 h to obtain white powdered pseudo hexagonal Nb₂O₅.^{38 (link)} Metal nitrates were used as the precursors for dopants Sr, Y, Zr and Ag. The atomic doping percentages for metal doped niobia were varied in the range of 0.05–2.5% and the resulting compounds were termed Nb_(2−x) M_xO_5−δ where x is the dopant% and M is the dopant. For preparing the doped metal oxide the same procedure was used, in addition, the respective dopant's metal nitrate precursor was mixed with the sonicated niobium precursor urea solution.