Electronic contributions to the elastic constants of tellurium-doped bismuth

Keyes' model for the electronic contribution to the elastic constants has been extended to the rhombohedral group Vb semimetal bismuth, and the magnitude of the effect calculated using parameters taken from the literature. The theory predicts that an increase in the free electron density should decrease C11, C66 and C44 and increase C12 and C14. These predictions have been tested by measuring the elastic constants of single crystals of bismuth heavily donor-doped with tellurium (1019-1020 electrons cm-3); the experiments were performed between 4.2K and room temperature by the ultrasonic pulse echo overlap technique. In general, doping of bismuth with tellurium causes the expected decrease in the ultrasonic wave velocities and the elastic constants vary in the manner predicted by the theoretical model. An increase in the free electron concentration causes C11 and C66 to decrease, C12 to increase, while the variation of C33 is negligible.