Effet photoplastique dans ZnS de structure blende entre 300 et 620 K

Deformation tests by uniaxial compression in the [110] direction have been performed on ZnS natural single crystals between 300 and 620 K in the dark and under illumination to study the protoplastic effect (P.P.E.). A positive P.P.E. (hardening), vanishing near 620 K, was revealed as well as a repeated yielding effect, the frequency and the amplitude of which were decreasing with increasing temperature. T.E.M. observations, the temperature dependence of the flow stress and the low values of the activation volume are consistent with dislocation glide being controlled by a Peierls mechanism in the dark as well as under illumination. The activation volume is always larger under illumination for a given T or π. This suggests an activation enthalpy larger under illumination. The P.P.E. could mainly originate from an illumination induced increase of the Peierls barrier