The Effect of Tension on the Electrical Resistance of Single Bismuth Crystals

Abstract

The compensated potentiometer method of measuring minute variation in small resistances which was developed by P. W. Bridgman has been used in the study of the effect of tension, applied parallel to the direction of current flow, on the resistance of single bismuth crystals. The tension coefficient of resistance at 30°C has been found to depend on the orientations both of the principal (111) and secondary ($11\overline{1}$) cleavage planes with respect to the tension. For the limiting case of the principal cleavage plane perpendicular to the tension, the coefficient is independent of the orientation of the secondary cleavage planes; in that of the principal cleavage plane parallel to the tension, the coefficient varies very little and is very probably independent of the secondary orientation. In the case where the normal to the principal cleavage plane makes an angle of about 60° with the tension, the variation of the coefficient with the orientation of the secondary cleavage plane seems to be a maximum. This variation involves a change in sign as well as in magnitude, so that for certain orientations the coefficient becomes positive instead of remaining negative. The coefficient shows trigonal symmetry, as it must do if it is to be consistent with the known corporeal trigonal symmetry of the bismuth crystal. The paper presents only these empirical results.