The effect of europium on structure and thermoelectric properties of silicon clathrates by HPHT synthesis

We have fabricated bulk clathrate materials Ba8-xEuxCu6Si40 via high-temperature and high-pressure (HPHT) method, and the structure combined with thermoelectric properties were characterized in detail. Even more surprisingly, this method took just an hour to synthesize clathrates with BaSi2 and EuSi2 as starting materials. The substitution of Ba by Eu has great impact on its microstructure and inevitably alters thermoelectric properties. Temperature dependent thermoelectric parameters have been measured from 320 K to 720 K. The measurements of electrical properties showed the degenerate semiconductor behavior. A minimum thermal conductivity of 1.26 Wm−1K−1 was reached at 720 K for Ba8Cu6Si40. The multi-scale hierarchical microstructure, from atomic scale to micro scale, can effectively enhance the phonon scattering, thus reducing the lattice thermal conductivity.