Study on Transport and Mechanical Properties of La and Ce Double Filled $p$-type Skutterudites*

Optimizing the thermoelectric performance of $p$-type skutterudites is extremely challenging due to several factors such as low Seebeck voltage and bipolar contribution in electrical and thermal conductivity at elevated temperature, leading to small \textit{ZT }value. In this work, we report improved thermoelectric performance of La and Ce double filled $p$-type skutterudites by melting-quenching-annealing-ball milling-hot pressing. The observed high power factor ($\sim $35 $\mu $W cm$^{-1}$ K$^{-2}$ at 500 $^{\circ}$C) and low thermal conductivity ($\sim $2.5 W m$^{-1}$ K$^{-1}$ at 500 $^{\circ}$C) leads to a peak \textit{ZT} about 1.1 in the optimized composition. With a $\Delta T$ of 475 $^{\circ}$C between heat source and sink, the estimated output power density in the best sample is $\sim $8 W cm$^{-2}$. The nano-indentation experiment reveals that the hardness and Young's modulus of elasticity of the sample is much better than Bi$_{2}$Te$_{3}$ and PbTe-based samples, indicating skutterudites is suitable for practical applications where mechanical strength is also important.