Synthesis of yttrium iron garnet (YIG) by citrate-nitrate gel combustion and precursor plasma spray processes

The influence of synthesis conditions on the formation of yttrium iron garnet (YIG) powders starting from the same precursor solution was investigated by employing a citrate-nitrate (C-N) gel combustion process and a precursor plasma spraying technique. Two different C-N ratios were used in the synthesis and their influences on phase formation were studied by thermal analysis (DTA/TGA) and X-ray powder diffraction (XRD). Time-resolved powder XRD experiments were performed for the first time on these C-N precursor materials to understand their mode of decomposition. For a C-N=0.75, the ex-situ XRD data confirmed a single-step conversion to YIG from the amorphous precursor powder without any intermediate phase formation. However, the use of the same C-N precursor solution as a liquid feedstock material in the precursor plasma spraying (PPS) technique revealed an entirely different transformation mechanism to YIG through the intermediate phase YFeO₃. The measured values of saturation magnetization (MS) as well as coercive field (HC) of the powder samples annealed at 1500 °C are close to those reported for bulk YIG.