Growth of Single Crystals and Bicrystals of Alkali Halides

Abstract

Techniques are described for the growth of large (6.3 cm2 by 15 cm) single crystals and bicrystals of NaCl. Grain boundaries from 2 to 45° mismatch across the interface were grown for pure tilt and pure twist misorientation in NaCl by the Czochralski technique. The method of crystal growth and the techniques required for good control of the misorientation and the planarity of the grain boundary are described. Similar techniques can be applied to KCl, LiF, and CsBr. The tilt grain boundaries of the NaCl bicrystals were found to be strong mechanically and not easily cleaved apart. The twist grain boundaries were very weak mechanically, especially at mismatch angles greater than 20°. Techniques and results for growing long thin single crystals of NaCl which have great flexibility and for observing the substructure of the growing interface of a single crystal are described.