High temperature thermoelectric properties of the type-I clathrate Ba8AuxSi46-x

The thermoelectric properties of the type-I clathrate Ba(8)AuxSi(46-x) (4.10 <= x <= 6.10) were characterized from 300 to 700 K. 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 (similar to 0.2 at around 600K for x = 5.59) beyond the level of the best Si-based clathrate compounds. (C) 2012 American Institute of Physics. [doi:10.1063/1.3682585]