Elastic Properties of MgB_2 and SiC-doped MgB_2 Superconductors

摘要

We investigated the elastic properties of MgB_2 and 5 wt.% SiC-doped MgB_2 superconductors utilizing the pulse-echo overlap technique. Longitudinal and shear ultrasound velocities were measured for each sample at 80 K and 300 K. The measured velocities at 80 K were used to calculate the various elastic moduli, i.e. longitudinal (Cl), shear (G), bulk (B) and Young's (Y) modulus, and the Debye temperature 6b, for both samples. The high θ_D at 694 K and 706 K obtained for MgB_2 and SiC-doped MgB_2, respectively, provide strong evidences via direct acoustic measurements to support numerous theoretical and non-acoustic data-based calculations. At 300 K, the higher longitudinal velocity of the pure MgB_2 compared to the doped MgB_2 but converging towards the same value of longitudinal modulus at 80 K, seems to suggest that the SiC-doped MgB_2 undergoes greater elastic stiffening through temperature range of 300 K down to 80 K. Using the θ_D values, the electron-phonon coupling constant X was calculated within the BCS framework and the two dimensional van Hove scenario. The results led us to conclude that MgB_2 is a moderately-strong coupled superconductor.