Growth Morphology of Hexagonal Selenium at High Pressures

Hexagonal selenium can be grown from the melt either in the form of spherulites or as single crystals. At normal pressures, the transition from spherulitic to single‐crystal growth habit is usually not seen due to the very slow growth rate of single crystals. At higher pressures, the single‐crystal growth rate is enhanced sufficiently to permit observation of this transition. Examination of melt‐grown crystals by Weissenberg x‐ray techniques disclosed a disorder normal to the ``c'' axis direction. The absence of the disorder in vapor‐grown needles produced at 5 kbar indicates that the disorder is built in during growth from the melt.