Comment on "Effective medium theory based modeling of the thermoelectric properties of composites: comparison between predictions and experiments in the glass-crystal composite system Si10As15Te75- Bi0.4Sb1.6Te3'' by J.-B. Vaney et al., J-Mater. Chem. C, 2015, 3, 11090

Vaney et al. have found that the thermopower formula for composites derived by Sonntag clearly fails to predict the thermopower of the man-made composites Si10As15Te75-Bi0.4Sb1.6Te3. The reason for this mistake was the fact that the thermal conductivities, ki and k, appearing in this formula were interpreted as the total thermal conductivities. However, only the electronic contributions to the thermal conductivities of the phases are to be taken into account. If this is considered, the thermopower formula is a good description for naturally grown composites. For man-made composites as considered in ref. 1, percolation elements should additionally be included as proposed by Vaney et al.