Numerical analysis of the magneto-Seebeck effect of bismuth with anisotropic band structureThe influence of the band structure of BiSb alloys on the magneto-Seebeck coefficient was estimated by the Boltzmann equation using an energy-dependent relaxation time approximation at 100 K. The magneto-Seebeck coefficient along the trigonal direction was calculated under a magnetic field along the bisectrix direction. The scattering factor was supposed as being an acoustic deformation potential scattering. In order to estimate the influence of band structure on the magneto-Seebeck coefficient, both two band and three band models were utilized. The two band model consists of an electron surface at the L-point and a hole surface at the T-point. The influence of the change in band overlap and the effective electron mass was investigated using the two band model. The three band model consists of an electron surface at the L-point and a hole surface at the T-point. The influence of change in the Sb concentration of BiSb alloy was also investigated using the three band model. As a result, the Seebeck coefficient was observed to increase as the band overlap decreased. The band overlap has little influence on the improvement of the magneto-Seebeck coefficient. The Seebeck coefficient decreases as the effective mass decreases; however, improvement in the magneto-Seebeck coefficient increases as the effective mass decreases. The magneto-Seebeck coefficient of Bi 95 Sb 5 was effectively improved under a low magnetic field.
We studied the influence of band structure on the Seebeck coefficient of bismuth under a magnetic field. In this study, the magneto-Seebeck coefficient was calculated by solving the Boltzmann equation with an energy-dependent relaxation-time approximation and by assuming the Lax model of the bismuth band structure, which contains the anisotropy of bismuth. The influence of the scattering factor on the magneto-Seebeck effect was also investigated in the anisotropic band structure. The magneto-Seebeck coefficient varies with the magnetic field direction. Improvement of the Seebeck coefficient under a transverse magnetic field is higher than that under a longitudinal magnetic field. For the acoustic deformation potential scattering, the Seebeck coefficient is improved in a low magnetic field. For other types of scattering, the absolute values of the Seebeck coefficient are decreased in the low magnetic field. Moreover, for scattering factor r of 0, the magneto-Seebeck coefficient for a parabolic band does not vary, while the magneto-Seebeck coefficient for a nonparabolic band decreases. The sign of the Seebeck coefficient was changed under a high magnetic field because of the increase in magnetoresistivity due to high electron mobility. The effect of impurity addition was also investigated by changing the Fermi energy. With increasing Fermi energy, the Seebeck coefficient is more easily affected by an applied magnetic field, because the electron density is increased.
We have used the finite-element method to calculate numerically the equations of electrical and thermal transport. The thermal conductivity of a wire array is analyzed. The influence of the wire array on the effective thermal conductivity of the element is discussed. The effective thermal conductivity decreases as the wire diameter is reduced. Decreasing the packing density significantly reduces the effective thermal conductivity. In the classical regime, the ratio of the effective electrical conductivity to the effective thermal conductivity of the wire array can be expressed as a function of packing density; this ratio decreases as the packing density decreases. The ratio for a wire array with realistic parameters is similar to that of bulk bismuth. Therefore, to improve the thermoelectric figure of merit, it is critical to enhance the intrinsic power factor in a wire by exploiting thermomagnetic or quantum effects.
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