We investigated the effect of ion nitriding on the crystal structure of 3 mol% Y2O3-doped ZrO2 (3YSZ) thin-films prepared by the sol-gel method. For this purpose, we used X-ray diffractometry to determine the crystalline phases, the lattice parameters, the crystal sizes, and the lattice microstrains, and glow discharge-optical emission spectroscopy to obtain the depth profiles of the elemental chemical composition. We found that nitrogen atoms substitute oxygen atoms in the 3YSZ crystal, thus leading to the formation of unsaturated-substitutional solid solutions with reduced lattice parameters and Zr0.94Y0.06O1.72N0.17 stoichiometric formula. We also found that ion nitriding does not affect the grain size, but does generate lattice microstrains due to the increase in point defects in the crystalline lattice. (c) 2005 Elsevier B.V. All rights reserved.