Preparation and characterization of Sr_0.09Ce_0.91O_1.91, SrCeO₃, and Sr₂CeO₄ by glycine–nitrate combustion: Crucial role of oxidant-to-fuel ratio

The title compositions were prepared by the gel-combustion process using glycine as the fuel and the corresponding metal nitrates as oxidants. The powders after calcination at 600 °C were characterized by x-ray diffraction for phase identification. The lattice parameters were refined by least squares method for each of the title compounds. Sr_0.09Ce_0.91O_1.91 could be prepared in situ, that is, without any further external heating at higher temperatures, whereas phase pure SrCeO₃ and Sr₂CeO₄ could be prepared only after calcination at 950 °C for 3 h. Sr_0.09Ce_0.91O_1.91 was prepared using three different oxidant-to-fuel ratios: the fuel-deficient ratio, the propellant chemistry (stoichiometric) ratio, and the fuel-excess ratio. The crystallite size as calculated by x-ray line broadening was found to be 13 nm, 20 nm, and 42 nm for the products from fuel-deficient, propellant, and fuel-excess ratios, respectively. It was found that the extreme fuel-deficient ratio of 1:0.5 failed to give phase pure Sr_0.09Ce_0.91O_1.91. The transmission electron microscopy studies showed that majority of the particles were in the range 80–100 nm and 200–250 nm for SrCeO₃ and Sr₂CeO₄, respectively. The compositional characterization was done by energy dispersive x-ray. A careful control of the oxidant-to-fuel ratio was found to be necessary to get the desired products, due to their different thermodynamic stabilities. Thus, the versatility of combustion process in synthesizing the products with different thermodynamic stabilities has been shown, which was hitherto unexplored.