1 Transport and mechanical properties of the double-filled p-type skutterudites La 0.68 Ce 0.22 Fe 4-x Co x Sb 12 Tulashi Dahal 1 , Hee Seok Kim 1 , Sonika Gahlawat 2 , Keshab Dahal 1 , Qing Jie 1 , Weishu Liu 1 , Yucheng Lan 1 , Kenneth White 2 *, and Zhifeng Ren 1 * 1 Department of Physics and Texas Center for Superconductivity, University of Houston, TX 77204 2 Department of Mechanical Engineering, University of Houston, TX 77204 *To whom corresponding should be addressed: kwwhite@uh.edu, zren@uh.edu Abstract Till date, the dimensionless figure of merit (ZT) of p-type skutterudites lags its n-type counterpart. In this work, we report improved thermoelectric performance of La/Ce double filled p-type skutterudites. The samples were synthesized by hot pressing nano-powder made by ball milling annealed ingots of La 0.68 Ce 0.22 Fe 4-x Co x Sb 12 with varying Co concentration. By tuning the Fe/Co ratio, we achieved a higher power factor (~35 μW cm -1 K -2 at 475 o C), leading to a peak ZT of 1.15 at 475 o C in La 0.68 Ce 0.22 Fe 3.5 Co 0.5 Sb 12 . Nanoindentation experiment carried on fine surface of the best sample reveals hardness of 5.4 GPa and modulus of elasticity of 126 GPa, which is much higher than those of Bi 2 Te 3 and PbTe based materials, indicating skutterudites are mechanically strong, good for some practical applications. © 2016. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/