SPACE-CHARGE POLARIZATION AND X-RAY-DIFFRACTION EXTINCTION REDUCTION IN SYNTHETIC AND NATURAL QUARTZ CRYSTALS

An X-ray diffraction study of alpha-quartz crystals with in situ elect ric field along the different crystallographic axes shows a strong enh ancement in the diffracted intensity. The effect is prominent in natur al crystals when the electric field is along the c-axis. This is evide nced by the increase in the intensity of X-ray rocking curves recorded from several crystals. The X-ray topographs recorded with in situ ele ctric field show extinction contrast consisting of striations parallel to the c-axis. This contrast disappears during irradiation in the abs ence of an electric field. The increase in the diffracted intensity an d the contrast on the topographs are explained by a model on negative space-charge collection.