Abstract
The characteristics of a possible dislocation etch for cadmium have been studied in detail and the factors affecting the action of the solution have been isolated. They are the orientation of the crystal surface and the composition of the etch. It has been shown that for reproducible etching the crystal surface must be parallel to a low index crystallographic plane to within +/-1° and the necessary techniques for preparing square cross-section crystals with such surfaces have been developed. The ionic compositions of the etch and the chemical polish employed, both solutions of nitric acid in ethanol, have been elucidated by chemical and spectroscopic methods and an attempt has been made to identify the fundamental mechanism of dislocation etching in the cadmium-etch system. The etch has been used to study the dislocations injected into cadmium single crystals sectioned by spark erosion machining. The experimental method used has novel features and it has been shown that the nature and depth of the damage introduced by this cutting technique depend on the spark energy employed and the diameter of the cutting wire used. This investigation has enabled thin foils free from sectioning damage to be prepared from bulk crystals and although lack of time has prevented a transmission electron microscopy study of deformed crystals reaching fruition, some observations made on foils prepared from undeformed crystals are recorded in an appendix. The etch has revealed that in crystals deformed in tension the dislocation density increases linearly with shear strain, a result at variance with the only previous report on this aspect of cadmium's behaviour. This report is critically appraised in an appendix. An attempt has been made to correlate the changes in the dislocation density of deformed and subsequently annealed crystals with their attendant changes in residual resistivity, dislocation density being estimated by the etch pit technique and residual resistivity by an a.c. mutual inductance method. An appendix presents a theoretical analysis showing how the complex components of the permeability of a rectangular section specimen placed in the a.c. apparatus may be computed.