Low temperature dislocation hysteresis losses in bismuth single crystals

In order to establish the parameters that govern the thermally activated motion of dislocations, we have studied the amplitude-dependent dislocation internal friction in pure undeformed bismuth single crystals with a [111] orientation over the temperature range 6–300 K and over a wide range of deformation amplitudes. Measurements were performed using a double composite oscillator technique at a frequency of 88 KHz for the longitudinal vibrations. Lowering of the temperature in the range 90–6 K causes the amplitude dependence of the decrement and of the modulus defect to move toward larger values of the amplitude, due to the thermally activated nature of dislocation depinning. The results are compared with the theory of Indenbom and Chernov. Quantitative analysis of the data in terms of this theory provides the activation energy and the activation volume for the depinning of dislocations at trapping centers as a function of the deformation amplitude. The force law is found for the interaction, and the distribution function for the length of the dislocation segments released is found to be a power law with an exponent of –4.9.

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