Polytype families in zinc sulphide crystals

Growth of unusual silicon carbide polytypes by island formation

“…However, in order to explain the growth mechanism of these isolated cases, certain modifications in the screw-dislocation mechanism are required. Mardix et al (1967) and Mardix & Kiflawi (1970) have proposed a mechanism called periodic slip for the growth of ZnS polytypes forming polytypic families. Because of many similarities between ZnS and SiC, the question first considered was whether periodic slip is a feasible mode of growth for SiC polytypes as well.…”

“…This characteristic difference between SiC and ZnS crystals arises because their modes of growth differ. A satisfactory explanation for the growth of ZnS polytypes forming polytypic families has been given by Mardix et al (1967). The present paper deals particularly with the growth mechanism of unusual SiC polytypes.…”

“…Polytypes having the same primitive periodicity along c, but different structures, constitute one polytypic family (Edward & Lipson, 1942;Wilson, 1942;Mardix, Alexander, Brafman & Steinberger, 1967). In particular, when a substance crystallizes into hexagonal as well as rhombohedral structures, the hexagonal polytypes of periodicity m and rhombohedral polytypes of periodicity 3m are said to constitute one polytypic family.…”

On the inapplicability of the layer-transposition mechanism to polytype formation in ZnS

“…The transformation takes place by expansion of basalplane stacking faults in the 2H parent structure on atomic planes spirally interconnected around a [00.1] screw dislocation. The experimental evidence for this model in vaporphase-grown ZnS includes: (a) all polytypes are of even order (Mardix, Alexander, Brafman & Steinberger, 1967); (b) polytypes in a given specimen occur in families (Mardix: Alexander, Brafman & Steinberger, 1967); (c) transformations can be induced even at room temperature by mechanical stresses ; (d)the polytypic regions are nearly perfect (Farkas-Jahnke & DornbergerSchiff, 1970;Steinberger, Alexander, Brada, Kalman, Kiflawi & Mardix, 1972); (e)there are exact correlations between homogeneous shear and crystal structure (Mardix, Kalman & Steinberger, 1968); (f) the generating screw dislocations were directly observed and their Burgers vector measured by X-ray topography (Mardix, Lang & Blech, 1971); (g) tilting was found to occur during the coolingdown period of the crystals .…”

New families of ZnS polytypes

“…During an investigation of ZnS polytypes, new polytypes were found, some of them belonging to hitherto unknown families (Steinberger & Mardix, 1967). The crystals investigated were ZnS platelets grown by sublimation at about 1200 C. Each crystal contains a large number of polytype regions having a common c axis.…”