We report the f ixing of photorefractive holographic gratings with high eff iciency in a sample of K12yLiyTa12xNbxO3 doped with Cu, V, and Ti. Holograms are thermally fixed through the screening of a photorefractive space-charge f ield by a nonphotoactive species at elevated temperatures. Fixed holograms are revealed by illumination at lower temperatures. Diffraction efficiencies of 25% in a 0.54-cm-thick sample are measured. Holograms undergo thermal decay with a 0.67-eV activation energy.