Damping of Dislocations in Niobium by Phonon Viscosity

Abstract

Attenuation measurements have been made of the body-centered crystal niobium for three waves along the 〈110〉 direction. The room-temperature measurements are consistent with dislocations lying in the (110) planes with glide directions along the 〈100〉 axes. The fast shear has the largest attenuation and it has been measured over a temperature range from 30° to 300°K with frequencies from 10 to 150 MHz. The attenuation can be divided into a square-law attenuation and a dislocation component. The dislocation component can be used to evaluate a drag coefficient which is nearly constant down to 78°K. It rises at low temperatures indicating an electron drag effect. The constant region is consistent with a phonon viscosity damping with a crystal having a peak in the thermal conductivity. The electron drag confirms a theoretical calculation giving a drag inversely proportional to the electrical resistivity.