The quartz-type orthophosphate was grown hydrothermally from acid solutions. During heating at 600 to 800C for several hours, defects which contained OH groups segregated into sub-microscopic bubbles which formed various patterns that were related to growth defects. The formation of oriented disks, star-like forms and helices was attributed to the passive climbing of step dislocation loops which sometimes originated at local growth defects. The growth dislocations were decorated, and revealed the effects of dislocation climb. The boundaries between growth zones and Brazil twin boundaries became clearly visible. Bands and growth striations were attributed partly to growth-condition fluctuations and partly to macro-step propagation. Such microscopic investigation of the patterns created by heat treatment was concluded to be a convenient method for the characterization and study of growth defects and dislocation dynamics.

Segregation Forming and Growth Defect Characterization by Heat Treatment of Hydrothermally Grown GaPO4. W.Wallnöfer, P.W.Krempl, F.Krispel, V.Willfurth: Journal of Crystal Growth, 1999, 198-199, 487-91