High temperature thermoelectric properties of the type-I clathrate Ba8AuxSi46-x
Résumé
The thermoelectric properties of the type-I clathrate Ba8AuxSi46-x (4.10 <= x <= 6.10) were characterized from 300 to 700K. Increasing the Au concentration leads to a transition from an n-type (x < 5.43) to a p-type (x > 5.43) electrical conduction. The experimental data are well described by a single-parabolic-band model assuming a single scattering mechanism of the charge carriers in this temperature range. The lattice thermal conductivity, inferred from degeneracy-adjusted Lorenz numbers, is low regardless of the composition. However, the measured values are significantly lower in the p-type samples possibly due to a combination of a higher degree of disorder in the crystal structure at high Au contents and an enhanced phonon-charge carrier coupling. Even though high thermopower values are achieved, the high electrical resistivity remains the main obstacle to push the dimensionless figure of merit ZT (0.2 at around 600 K for x = 5 .59) beyond the level of the best Si-based clathrate compounds.
Domaines
Physique [physics]
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