Effect Of Al Doping On Thermoelectric Power Of Mgi__x Al_xB2 Phonon Drag And Carrier Diffusion Contribution

摘要

The carrier diffusion contribution to the thermoelectric power (S_c~(diff)) is calculated for MgB_2,Mg_(0.9)Al_(0.1)B_2 and Mg_(0.8)Al_(0.2)B_2 within two energy gap method. The phonon drag thermoelectric power (S_(ph)~(drag)) in normal state dominate and is an artifact of strong phonon-impurity and phonon scattering mechanism. The conductivity within the relaxation time approximation for π and σ band carriers has been taken into account ignoring a possible energy dependence of the scattering rates. Both these channels for heat transfer are clubbed to get total thermoelectric power (Stotai) which starts departing from linear temperature dependence at about 150 K, before increasing at higher temperatures weakly. The anomalies reported are well accounted in terms of the scattering mechanism by phonon drag and carrier scattering with impurities, shows similar results as those revealed from experiments.