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Metastable YFeO 3 with the hexagonal YAlO 3 structure was obtained by a sol-gel process at 700 °C, using metal nitrate precursors with pH control and the appropriate citric acid to nitrate ratio. Under similar conditions, YFe 1-x Pd x O 3-δ (0 < x e 0.1) compositions were also prepared. The substitution of Fe by Pd stabilizes the YAlO 3 structure at higher temperatures. The crystal structures of YFe 1-x Pd x O 3-δ (0 e x e 0.1) were refined by Rietveld analysis of X-ray and neutron powder diffraction data. The parent hexagonal YFeO 3 (x ) 0) crystallizes in the space group P6 3 /mmc with a ) 3.5099(3) Å and c ) 11.759(2) Å. The redox-driven mobility of Pd to integrate into the oxide host as ions and to dissociate from it as fcc-Pd nanoparticles was monitored by a combination of X-ray diffraction and X-ray photoelectron spectroscopy. Pd nanoparticles in the reduced samples were detected by scanning backscattered electron microscopy and transmission electron microscopy. The Pd 2+ -containing materials showed significant low-temperature (near 100 °C) catalytic activity for CO oxidation, comparable to that of highly dispersed PdO/Al 2 O 3 , despite their relatively low surface areas.