The microstructure of ZrO2 fine particles produced by a novel synthesis method at 450 degrees and 950 degrees C has been studied. The fundamentals of the synthesis method, which involves both chemical and diffusion phenomena, are presented. The method is based on mass transport through the gaseous phase between metallic zirconium and Fe2O3 powder. The mass-transporting chemical species are zirconium and iron chlorides. This article focuses on the microstructure and structure of ZrO2 particles formed by the reaction between gaseous ZrCl4 and solid Fe2O3, which is a relevant reaction step that occurs during the synthesis process. The resulting ZrO2 crystals grown on Fe2O3 particles have been analyzed using transmission electron microscopy, Microstructural characterization has been complemented by X-ray diffractometry analysis. Tetragonal-ZrO2 is produced at 450 degrees C and monoclinic-ZrO2 single crystals are produced at 950 degrees C.