Imperfections in (010) and (001) crystals were studied by means of X-ray diffraction topography. The results showed that 2 types of dislocation (spiral and ordinary), which were both distributed with an unexpectedly high density and ran almost normal to the (001) face, played an important role in increasing the growth rate of the (001) plane by providing self-perpetuating growth steps or growth centers. The spiral dislocations produced so-called white Borrmann images, and their contrast decreased with decreasing specimen thickness and Borrmann coefficient. The images lost their fine spiral details when a contrast inversion from white to black occurred.

Q.L.Zhao: Journal of Applied Crystallography, 1994, 27[3], 283-7