ANISOTROPY OF THE ELECTRON AND HOLE DRIFT MOBILITY IN KNBO3 AND BATIO3

We determine the anisotropy of the mobility of photoexcited charge car riers in single crystals of KNbO3 and BaTiO3 by means of a purely opti cal method. In orthorhombic KNbO3 the mobility anisotropy is measured for both electrons and holes giving mu(a)/mu(c) = 1.05 +/- 0.06, mu(b) /mu(c) = 2.9 +/- 0.3 for electrons and mu(a)/mu(c) = 1.15 +/- 0.09, mu (b)/mu(c) = 1.9 +/- 0.2 for holes. In BaTiO3 we find for holes mu(a)/m u(c) = 19.6 +/- 0.6. Our experiment also demonstrates that the acousti c phonon contribution to the dielectric permittivity is substantially different for spatially modulated electric fields as compared to the h omogeneous case.