Abstract Powders and thin films of Y-Al-O were synthesized by introducing atomized solutions of Y and Al chlorides or nitrates into an argon inductively coupled plasma at high temperatures above 5000K (the spray-ICP technique). The powders consisted of spherical fine particles of 10–50nm diameter, and were mixtures of amorphous and crystalline material whose phase varied from Y 4Al 2O 9 to hexagonal (h-) YAlO 3 depending on the metal ratio of Y:Al in the precursor solutions. No garnet type Y 3Al 5O 12 was formed even when the Al to Y ratio in the solution was increased past the garnet composition. Films were prepared on single-crystal sapphire surfaces having no background reflection peaks in X-ray diffraction. The films had fine columnar structures, and exhibited a (001) orientation of h-YAlO 3 in the Al-rich region above Y:Al=1:1 in molar ratio. Particle formation occurred by the condensation of oxides from the gas phase formed by the evaporation and reaction of metal salts. h-YAlO 3 was formed as a stable intermediate compound in the deposition process.