Silicon single crystals were deformed in tensile tests along the  direction between 1173K and 1373K. The yield point phenomenon was observed in the specimens deformed below 1273K, while a continuous yield was observed in the specimens deformed above 1323K. The values of work-hardening rate in stage II were the same as those reported in other single crystals. Orientation maps of the specimen obtained by using electron backscattered electron diffraction method indicated that stage II starts before the Schmid factor of the secondary slip system became larger than that of the primary slip system. Because of the constraint due to the gripping of the test piece, kink bands are formed during stage I before the onset of stage II, and then the stress state becomes non-uniaxial. This suggests that the formation of kink bands triggers the activation of the secondary, i.e., conjugate slip system to increase the resolved shear stress on the conjugate slip systems.
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