Twinning of Crystals due to Differences between the Most Favourable Symmetric and Energetic Structural Arrangements, Part II

Twins and oriented intergrowths are often caused by structural instabilities. A conflict arises between the highest symmetric and the most favourable energetic structural arrangement. A necessary condition for twin growth is the presence of lattice pseudosymmetries. This was shown with two additional examples, maleic acid and 3,5‐dimethylbenzoic acid. Both substances are known practically only as twins. Using lattice‐energy calculations, energetic arrangements that are more favourable were found in both cases. These structures explain the transition that can exist between the twin crystal parts.