High-Density Single-Phase Yttrium-Gadolinum-Iron Garnets by Spray Drying

Yttrium–iron garnet (YIG)-based ceramics are largely used in microwave devices, sensors, lasers, phosphorescent sources, and magneto–optical applications. In this research, high-density, single-phase Gd(0.4)-YIG were obtained by spray drying starting from nonstoichiometric, iron-rich, metal nitrate solutions. Aqueous metal nitrate solutions, containing polyvinyl alcohol (PVA) and polyethylene glycol (PEG), were prepared and sprayed to obtain precursor powders. In some cases either sulfuric acid or hydrochloric acid were added to the initial solution. On the basis of differential thermal analysis and thermogravimetry analysis, as-sprayed powders were calcined between 600°C and 1200°C and then characterized by induced coupled plasma spectroscopy, X-ray diffraction, and high-temperature X-ray diffraction. According to thermal dilatometry results, powders calcined at 1200°C were sintered in air up to 1470°C. The microstructure of sintered ceramics was made up of fine grains, being an average size of about 10 μm. It was found that addition of an inorganic acid to the precursor solution is essential to obtain high-density (98%) sintered materials. Ferromagnetic resonance linewidth (ΔH−3 dB) measurements on sintered materials were also performed.