Application of the faulted matrix model to the growth of polytype structures in mica

Abstract

Following Baronnet's theoretical deduction of the possible polytype structures in mica that can result from spiral growth round single screw dislocations of different Burgers vectors created in a perfect matrix, this paper reports a systematic deduction of mica polytypes on the basis of the faulted matrix model, proposed earlier by Pandey and Krishna to explain the growth of polytype structures observed in SiC, CdI 2 and PbI 2. All possible intrinsic and extrinsic fault configurations are worked out that can occur in the basic structures of mica, namely 1M [0], 2M 1 [2 2 ] and 3T [222]. The most probable fault configurations for each basic structure are predicted by estimating the relative stacking fault energies (SFE) of all possible fault configurations. Polytype structures that can result by spiral growth round screw dislocations of different Burgers vectors originating in faulted basic structures of mica are deduced by considering the most probable fault configuration to lie at different distances from the surface at the time of the origin of the screw dislocation step. Of the various structures resulting from screw dislocations of the same Burgers vector, the structure having the lowest SFE would be more probable. The most probable series of structures so predicted are found to be in excellent agreement with those observed.