ELECTRON-MICROSCOPIC INVESTIGATION OF AGBR NEEDLE CRYSTALS

Needle shaped AgBr crystals are investigated using electron diffraction and conventional transmission electron microscopy. It will be shown that the particular morphology and growth of the needles result from the defect structure of the crystals, which consists of three non-parallel twin planes, i.e. two (111) type and one (221) type twin planes. Unilateral growth is shown to occur in a [110] type direction, being the intersection of the two non-parallel (111) twin planes. On both ends of the needle, three self-perpetuating reentrant grooves are present, responsible for the rapid growth of the needle.