The low-frequency impedance spectroscopy method has been used to investigate the electrical conductivity peculiarities of lithium niobate (LN) crystals reduced in hydrogen. It has been found that the activation energy value of the dark electrical conductivity of such crystals in a temperature range of 288...370 К is equal to 0.68±0.02 eV. It has been demonstrated that the multiple heating of «black» LN crystals up to a temperature of about 420 K results in surface layers with modified electrical properties to occur in the crystal’s polar faces. The electrical conductivity mechanism of LiNbO3 crystals reduced in the hydrogen-containing atmosphere, and the causes of the instability of these properties are discussed.

The temperature dependence of the dark electrical conductivity of the LiNbO3(LN) crystals annealed in saturated H2O and D2O vapor in the range 293...400 K is investigated. It is found that the activation energy of the electrical conductivity is equal to (0.71 ± 0.02) eV and is close this value of LN samples, reduced in hydrogen. Annealing in ampoules with H2O vapor also lead to LN optical spectra changes such annealing in H2. The nature of this phenomenon is discussed.

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The electrical conductivity of single crystals of lithium tantalate and lithium niobate of the con gruent composition not subjected to special thermochemical treatments has been investigated in the temper ature range of 290-450 K. It has been shown that the charge transfer mechanisms and carrier types in these crystals are identical in the temperature range under study. The presence of mobility anisotropy of conduction electrons has been revealed and its influence on the recording and storage of optical phase holograms in these crystals has been established.

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