Decays of the diffraction efficiency of gratings written in Fe:LiNbO3have been studied in connection with photorefractive fixing. Measurements have been carried at five different temperatures within the range of interest in photorefractive fixing, 144–168 °C. The decay curves are nonexponential and can be fitted to a sum of three simple exponential components, whose effective activation energies and preexponential factors have been determined. The dependence of the last exponential component on the grating period &Lgr; has been measured and a 1/&Lgr;2law has been found. The decay constants have also been found to depend on the time the crystal is kept at the setting temperature before writing the grating. The difficulties for establishing a model taking into account the occurrence of several sites for protons in LiNbO3are discussed. ©1995 American Institute of Physics.