Periodic slip processes and the formation of polytypes in zinc sulphide crystals

Abstract

Inherent deformations of ZnS polytype regions are determined by measuring angles between linear markings. The deformations are correlated to the crystallographic structures of the polytypes as well. The relations clearly indicate that polytype formation occurred by a periodic slip process after crystal growth had been completed. Further observations substantiating this model are quoted.

The formation of macroscopic polytypic regions in ZnS crystals

“…The walls of the hollow tubes in different regions along the c axis of the specimen are found to be shear-deformed, with the shear perpendicular to the c axis in unison with the prismatic faces of the crystal. This effect is a direct consequence of the periodic-slip process and was discussed in detail in a former publication (Mardix, Kalman & Steinberger, 1968). The direction of the c axis in Fig.…”

“…The mechanism of the 'periodic-slip process" (Mardix, Kalman & Steinberger, 1968) of polytypic formation has by now a large volume of supporting experimental evidence (Alexander, Kalman, Mardix & Steinberger, 1970;Mardix, Lang & Blech, 1971). The same mechanism was found to be operative also in the formation of TiS polytypes (Legendre, Motet, Tronc & Huber, 1975;Legendre & Huber, 1977).…”

Further studies on the phase transformation in cadmium iodide polytypic crystals

“…To date the most detailed studies of polytypic phase transformations have been carried out for zinc sulphide (Secco d'Aragona, Delavignette & Amelinckx, 1966;Mardix & Steinberger, 1966;Mardix, Kalman & Steinberger, 1968) and cadmium iodide (Lal & Trigunayat, 1970;Tiwari & Srivastava, 1972). On the basis of these investigations, it is generally believed that the phase transformation in polytypic crystals occurs as a result of nucleation, propagation and rearrangement of stacking faults.…”

“…It was found that in none of the crystals studied did any noticeable change in shape occur. This shows that the present transformations were not martensitic (Daniels, 1966;Mardix, Kalman & Steinberger, 1968). A local polytypic region, embodying a single partial dislocation ribbon and the accompanying stacking faults, was located by looking at thin crystals in an electron microscope under transmission and selecting an area exhibiting a single partial dislocation ribbon.…”

“…The calculated tilt angle was found to agree with the measured tilt angles. Prior to the work of Alexander et al Danieis (1966) and Mardix, Kalman & Steinberger (1968) studied 2H--+ 3C transformations in zinc sulphide and suggested that the phase transformation proceeds through periodic slip processes embodying rotation and climb of partial dislocations around a screw dislocation parallel to [00.1]. In the case of lead iodide crystals, phase transformations have been studied recently by Prasad & Srivastava (1973) and it has been suggested that low-identity-period polytypes transform to higher-periodicity polytypes through the nucleation, propagation and rearrangement of stacking faults.…”