Solubility study of Yb in n -type skutterudites YbxCo4Sb12 and their enhanced thermoelectric properties

The solubility of Yb in ${\text{Yb}}_{x}{\text{Co}}_{4}{\text{Sb}}_{12}$ was reported to be 0.19 in bulk skutterudites made by melting and slow cooling method. Surprisingly we increased $x$ close to 0.5 by a special sample preparation method: ball mill and hot press. We show that a higher Yb concentration not only increases the power factor due to a higher electron concentration but also reduces the thermal conductivity $k$ because of stronger phonon scattering. In this way, we have achieved a dimensionless thermoelectric figure of merit ZT of about 1.2 at $550\text{ }\ifmmode^\circ\else\textdegree\fi{}\text{C}$ in ${\text{Yb}}_{0.35}{\text{Co}}_{4}{\text{Sb}}_{12}$.