Dislocations in α-sulphur

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Abstract
It is suggested that the orthorhombic α-sulphur structure can be viewed as an elongated f.c.c. lattice with c-axis about twice as long as α-and b-axes. Such a model should favour {111} slip interfaces through which four-plane blocks can glide by the usual ½〈110〉, ½〈011〉 and ½〈101〉 lattice periods. It is proposed that the brittle nature of the solid results from the fact that this {111} slip is limited by special (sessile) dislocation dissociation, to form Lomer-Cottrell like barriers, rather than from high lattice friction as is often proposed for molecular solids. The possible existence of wide faults in the {111} stacking is discussed.