Electrical resistivity measurements of lattice defects in hexagonal close packed metals
Lattice defects produced in zinc and cadmium by plastic deformation at 78 K have been investigated by means of electrical resistivity measurements at 78 K. Single crystals and polycrystalline samples of both metals have been used. The annealable increase in the resistivity of single crystals with deformation is generally less than 0.5% for deformations of up to 5% in zinc and 10% in cadmium. This is too small for annealing stages to be resolved satisfactorily, particularly since they are obscured by irregular changes in resistance during annealing, attributed to anisotropic thermal expansion of neighbouring sub-grains. Polycrystalline zinc is too brittle to allow significant deformation at low temperature, but a measurable resistivity increase has been produced in polycrystalline cadmium. The increase is proportional to strain, with a coefficient (12.5 ± 0.7) nQm per unit strain, half due to dislocations and half to point defects. This value is consistent with the point defect production mechanism being nonconservative movement of dislocation jogs, producing a defect concentration of 0.1% per unit strain, the resistivity of defects being 60 nΩm per 1% atomic concentration. Isochronal and sequential isothermal annealing was performed, and the activation energy was determined by an improved version of the change-of-slope method which eliminates the necessity for subjective curve-fitting operations. The annealing spectrum was divided into three stages: stage III, at 80 to 130 K, activation energy 0.16 ± 0.03 eV; stage IV, at 130 to 180 K, activation energy increasing from 0.2 eV to -0.4 eV; and stage V, 180 to 220 K, 0.7 ± 0.1 eV. There was no unique order of kinetics at any stage, and it appears that a number of overlapping processes took place. Stage III is attributed to the annealing of interstitials and stage IV to vacancies, but both these defects probably moved in groups of two or more and interacted with impurities. Stage V is attributed to dislocation rearrangement.