Deformation twinning in materials of the A 4 (diamond) crystal structure

Abstract
Deformation under certain conditions causes twinning in silicon, germanium, gallium antimonide, indium antimonide and zinc blende which have the A4 crystal structure. In material beneath hardness impressions formed at elevated temperatures a flow stress is superimposed upon hydrostatic compression; under these circumstances deformation twins form at temperatures between 0$\cdot $44 and 0$\cdot $74 of the absolute melting-points. Twins of the {111} type and, except in the case of zinc blende, of {123} type have been observed. Minor boundaries of thick growth twins may be {123} planes which also form boundary faces of etch pits. The only coherent interface possible between a {111} twin and matrix is a {111} plane; it is shown that among semi-coherent boundaries a {123} plane gives the best fit. The translational shears for twinning have been determined: for (111) twinning the shear is 0$\cdot $4084 a in the [11$\overline{2}$] direction with ($\overline{1}$10) as the shear plane; for (123) twinning the shear is 0$\cdot $6552 a in [41$\overline{2}$] direction with (1$\overline{2}$1) as the shear plane; where a is the parameter of the A 4 unit cell.

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