REINVESTIGATION OF THE RE-ENTRANT CORNER EFFECT IN TWINNED CRYSTALS

Morphological characteristics of twinned crystals, such as flattened or elongated morphology have so far been explained in terms of the re-entrant corner effect at twin junction, which was originally proposed as preferential growth site for perfect crystals. The validity of this effect has been critically re-investigated for real crystals. It is shown that this effect in its original sense can operate only under low supersaturation and only for perfect crystals containing no screw dislocations. For real crystals containing screw dislocations, no re-entrant corner effect will be expected whatsoever. Flattened or elongated morphology of twinned crystals is due to either pseudo re-entrant corner effect or one-directional growth along the twin junctions, both resulted from screw dislocation bundles concentrated in the composition plane. © 1979.