Sub-grains were easily introduced into LaB6 crystals. Their density increased with rotation rate during crystal growth. The sub-grains were cubes, 0.2 to 0.5mm in length; generated parallel and perpendicular to the [100] growth axis. The most effective way of preventing sub-grain generation was to grow a single crystal without crystal rotation, with a stationary molten zone. The sub-boundary in a crystal had a La-rich component as well as a La-rich composition in the molten zone. Sub-grain generation was considered to be a cellular structure generated by the constitutional supercooling mechanism.

Subgrains in LaB6 Crystals Grown with a Xenon Arc Image Furnace. Aida, T., Fukazawa, T.: Journal of Crystal Growth, 1987, 80[1], 9-16