Abstract
The pressure dependence of sound velocity of longitudinal and shear waves were measured up to 0.5 GPa using a pulse echo overlap method on polycrystalline single-phase MgB 2 superconductor which was high pressure synthesized and with a T c of 39 K. The pressure dependence of Debye temperature and specific heat were calculated based on sound velocity data. The results indicate that Debye temperature increases with the applied pressures while specific heat decreases. The Grüneisen constant was calculated as well. From the sound velocities, the pressure coefficient of the averaged phonon frequency was obtained, which is consistent with the value estimated by Vogt et al. This indicates that the importance of phonon hardening in the variation of T c under pressure. Upon changing the Debye temperature, unit cell volume and transition temperature with the pressure, volume dependence of electron-phonon coupling constant are also calculated.
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