Ultrasonic Measurements in Single-CrystalNb3Sn

Ultrasonic-velocity and attenuation measurements in ${\mathrm{Nb}}_3$Sn indicate anomalous temperature dependences of the elastic moduli and sound absorption. At room temperature, the elastic moduli and the attenuation of 555-Mc/sec compressional waves are typical of those found for metals. The room-temperature elastic moduli have been determined as $C_{11}=2.538\mathrm{}$, $C_{12}=1.124\mathrm{}$, and $C_{44}=0.3957\mathrm{}$ in units of ${10}^{12}$ dyn/${\mathrm{cm}}^2$. At 4.2°K, $C_{11}$ and $C_{44}$ are reduced by 35.1% and 32.8%, respectively, while $C_{12}$ is increased by 46.4%. At 32°K, and at the superconducting-transition temperature, there are peaks in the attenuation-temperature curve. Below 18°K, the attenuation is temperature-independent.