Abstract
Microdefects in striated (swirls: A and B-defects) and non-striated distribution (D-defects) were observed in dislocation-free crystals with relatively large diameters by x-ray topography following copper decoration. Impurity effect on formation of both the defects was studied by doping with B, C, P and O impurities: Swirl formation is enhanced by doping with by B, C and P, and hindered by O impurity. Whereas, D-defect formation was suppressed by C impurity, and their distribution was striated by O impurity. Comparison of D-defects and swirl defects (interstitial type dislocation-loops) led to the inference that D-defects are clusters of frozen-in vacancies. It was found that the temperature gradient at the interface associated with the growth rate is the critical condition for formation of both the defects rather than the cooling rate. The swirl formation is explained by two actions of the high temperature gradient at the interface: (1) It produces a high stress field to expand their sizes. (2) It decreases concentration of vacancies by out-diffusion to lower the effect by mutual annihilation of interstitials and vacancies.
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