Material parameters relevant to the photorefractive effect in the paraelectric phase are compared for KLTN doped with iron and KLTN doped with copper. Unlike copper-doped crystals, iron-doped KLTN shows an efficient thermal fixing process occurring at room temperature. Measurements as a function of temperature and applied field reveal the compensation to be a thermally activated process with an activation energy of 1.05 eV, but the process is only weakly dependent on field. FTIR measurements indicate the presence of hydrogen and conductivity measurements suggest that hydrogen migration is the dominant contribution to the conductivity, reinforcing the conclusion that the crystals show "thermal fixing" at room temperature.
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