Cubic yttria-stabilized zirconias (YSZs) (15 mol% Y2O3) doped with 2 wt% CuO and 0.3 wt% Fe2O3, respectively, have been compared with undoped YSZ. The lattice constants were found to increase in the sequence : a(YSZ) < a(YSZ/Fe) < a(YSZ/Cu). Vickers microhardness of polycrystalline YSZ/Fe exceeds that of polycrystalline YSZ/Cu, whereas the hardness of the single crystalline materials YSZ/Fe and YSZ/Cu are nearly identical and consistently lower than the polycrystalline values. Raman and infrared spectra reveal a breakdown of the selection rules, i.e. these techniques probe the local, non-cubic arrangement of oxygen vacancies. The findings are discussed in terms of a substitutional versus an interstitial-doping model.