Electronic contributions to te elastic constants of bismuth and bismuth alloys

Abstract

The Keyes model has been used to formulate the free electron contribution to the elastic constants of bismuth and its alloys with antimony (0-10 at.% Sb) The electronic contribution has been shown theoretically to be negligible in the intrinsic materials but to be observable in highly donor doped bismuth. The elastic stiffness constant tensor components of single crystals of bismuth and its alloys (3 at.% Sb, 5 at % Sb, 7 at.% Sb end 10 at.% Sb) with antimony have been obtained between 4.2 K and room temperature from measurements of ultra sonic wave velocities made by the pulse echo overlap technique. In contradiction with previous work, on polycrystalline alloys the ultrasonic velocities are found to increase monotonically with antimony composition. No electronic contribution to the elastic constants can be observed. The temperature dependences of the elastic constants are independent of the antimony concentration. The elastic constants of bismuth doped with tellurium (0-0.4 at.% Te) have been measured between 4.2 K and room temperature. Changes in some of the elastic moduli have been attributed to electronic contributions, the magnitudes of which are in reasonable agreement with the theoretical predictions. The temperature variation of the ultrasonic velocities, which are independent of tellurium composition, have been explained on the basis of temperature dependent deformation potentials.