Morphology and twin plane structure of silver bromide rod crystals

Large silver bromide rod crystals have been grown in a solution of silver bromide and potassium bromide in dimethyl sulfoxide. Samples of these crystals were examined by scanning electron microscopy in order to study their side and top face structure. Crystal sides were bounded by {111} and {100} faces. Rod crystals grown from concentrated solutions developed a well-defined top face structure composed of alternating {111} and {100} faces. However, they showed a relatively small length to thickness ratio. On the other hand, top faces of fast growing rod crystals were rough. Slices of rod crystals were examined by transmission electron microscopy to study their twin plane structure, for the first time. All the rod crystals examined showed non-parallel twin planes of (111) type. Surprisingly, all of them also showed parallel twin planes. Rod crystals can transform into tabular or tetrahedral crystals either by formation of new twin planes, or by overgrowth of some twin variants over others in processes that start at the tips of the rod.