ZrO2 thin films have been prepared at room temperature by ion beam induced chemical vapour deposition (IBICVD). Two different sets of samples have been prepared depending on whether O-2(+) or mixtures O-2 + Ar+ ions were used for the decomposition of the precursor. The structure, microstructure, surface roughness and optical properties (i.e, refraction index) have been determined for the two sets of samples. The 'as prepared' samples were very compact and dense and had a very low surface roughness. The (O-2(+))-ZrO2 samples were transparent and had a high index of refraction (n = 2.20 at lambda = 660 nm). On the contrary, the (O-2(+)-Ar+)-ZrO2 films showed a greyish aspect after preparation, probably because of the existence of lattice defects in their structure. These defects were removed by annealing in air at TT 573 It. Then, the films became transparent and had a slightly lower refraction index than that of the O-2(+)-ZrO2 films subjected to the same thermal treatments. For the (O-2(+)-Ar+)-ZrO2 thin films, it was shown by X-ray photoelectron spectroscopy (XPS) and Rutherford back scattering (RBS) that Ar (4 at.%) remained incorporated within the oxide lattice even after annealing at T = 773 K. The incorporation of Ar atoms within the ZrO2 network induced significant modifications in the crystallographic structure of the films. Thus, while X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) showed that the (O-2(+))-ZrO2 films consist of a mixture of of monoclinic and tetragonal phases of zirconia, the (O-2(+)-Ar+)-ZrO2 films depicted, at 298 K, a high degree of amorphisation. However, these films yielded a cubic/tetragonal phase after annealing at T > 573 K. The role of the embedded Ar in inducing these structural changes is discussed.