Comparison of citrate-nitrate gel combustion and precursor plasma spray processes for the synthesis of yttrium aluminum garnet

The influence of synthesis conditions on the formation of yttrium aluminum garnet (YAG) powders starting from the same solution precursors was investigated by employing a citrate-nitrate gel combustion process and a precursor plasma spraying technique. YAG powders were formed at ≥500°C, through the citrate-nitrate gel combustion process, without any intermediate phase formation. Time-resolved x-ray experiments were performed for the first time on these citrate-nitrate precursor materials to understand their mode of decomposition. The in situ data confirmed a single-step conversion to YAG from the precursor powder without any intermediate phase formation. Ex situ experiments also produced similar results. However, the use of the same citrate-nitrate precursor solution as a liquid feedstock material in the precursor plasma spraying technique revealed an entirely different transformation mechanism to YAG through intermediate phases like H-YAlO₃ and O-YAlO₃.