Phonon Drag Effect in Nanocomposite FeSb2
  We study the temperature dependence of thermoelectric transport properties of four FeSb2 nanocomposite samples with different grain sizes. The comparison of the single crystals and nanocomposites of varying grain size indicates the presence of substantial phonon drag effects in this system contributing to a large Seebeck coefficient at low temperature. As the grain size decreases, the increased phonon scattering at the grain boundaries leads to a suppression of the phonon-drag effect, resulting in a much smaller peak value of the Seebeck coefficient in the nanostructured bulk materials. As a consequence, the ZT values are not improved significantly even though the thermal conductivity is drastically reduced. 
Mani Pokharel, Huaizhou Zhao, Kevin Lukas, Bogdan Mihaila, Zhifeng   Ren, and Cyril Opeil
cond-mat.mes-hall cond-mat.mtrl-sci