Photocurrents in doped LiNbO3 crystals are shown to be due to a bulk photovoltaic effect with saturation voltages in excess of 1000 V (∼105 V/cm). This effect accounts for the light-induced index changes in LiNbO3. An explanation of the photovoltaic effect, based on the asymmetry of the lattice, is proposed.

Alkali niobate and tantalate glasses have been prepared by rapid quenching. These glasses exhibit room-temperature ionic conductivities as high as 10−5 (Ω cm)−1 and electronic conductivities less than 10−11(Ω cm)−1. In the case of LiNbO3, the glass conductivity is many orders of magnitude greater than that of the single crystal. These conductivities are sufficiently high for rapidly quenched vitreous oxides to be considered for applications as solid electrolytes.

Raman scattering studies of La2CuO~have revealed a high-frequency component {-3000 cm ') which we interpret as due to scattering by spin pairs. Comparison of the spectra with those of K2Nipg leads to a value of J -1100 cm ' for the exchange interaction. The twodimensional nature of the fluctuations suggested by earlier neutron scattering work is indicated here by the insensitivity of the spectra to temperature as well as to departures from stoichiometry which strongly inhuence the three-dimensional ordering temperature T~.A common feature of the high-temperature

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