Morphology of β‐BaB 2 O 4 (BBO) in relation to its crystal structure and growth conditions

A periodic bond‐chain (PBC) analysis has been made of the structure of β ‐BaB 2 O 4 (BBO) and related to crystal growth conditions, in order to explain the sometimes tangerine‐shaped, sometimes needle shaped crystals that are observed when BBO is grown experimentally. The periodic bond chains generate eight‐connected nets in BBO. The order of morphological importance (MI) of these F faces is determined by comparing the nearest‐neighbour interaction ionic bond energies. The results are compared with experimental data. Six faces, sometimes observed parallel to the c axis of BBO, were identified as the hexagonal prism {110}. Two other forms are either the trigonal pyramids {012} and {01} or the trigonal pyramids {102} and {01}. {0001} is an important cleavage plane. The tangerine habit is a result of the strong temperature gradient, which is often used when growing BBO. The isotherms of the furnace impose their habit on the growing crystal.