Yttrium-doped BaZrO 3 powders have been synthesized by sol-gel method. Powder XRD confirms that BaZr 1− x Y x O 3− δ ( x = 0.00, 0.05, 0.10) crystallize with the perovskite-type unit cell (space group Pm 3 ‾ m ). The effects of doping and hydration on the band gap of BaZr 1− x Y x O 3− δ have been evaluated through the analysis of the diffuse reflection spectra. An additional absorption band is observed near the fundamental absorption edge in the doped samples annealed in dry oxygen. These findings are explained by the impact of defects on O(2 p )–Zr(4 d ) charge transfer transitions and by trapping of electrons by oxygen vacancies. [ABSTRACT FROM AUTHOR]