Enhancement of thermoelectric properties of Yb_0.25Co₄Sb₁₂ skutterudites through Ni substitution

In this work, we investigate the effects of Ni doping on the thermoelectric (TE) properties of Yb_0.25Co₄Sb₁₂ sample. Yb_0.25Co_4xNi_xSb₁₂ (0 ≤ x ≤ 0.5) samples were prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The morphology of consolidated samples were characterized by X-ray diffraction (XRD) and scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS). The thermoelectric properties of bulk samples were measured from room temperature to 800 K. The XRD analysis confirmed that, the successful formation of the Co₄Sb₁₂ skutterudite phase and Ni is substituted into Co site of the skutterudite crystal lattice. Moreover, the electrical resistivity decreased to 14.6 μΩm at 785 K for Yb_0.25Co_3.5Ni_0.5Sb₁₂ sample, due to increase of the electron concentration by Ni-addition. The absolute Seebeck coefficient reached the highest value of 223 μV/K at 592 K for Yb_0.25Co_3.7Ni_0.3Sb₁₂ sample, thus yielding a maximum value of power factor of 2.41 × 10^-3 W/mK² at 592 K. The highest dimensionless thermoelectric figure of merit value ZT of 0.49 at 692 K has been achieved for the Yb_0.25Co_3.7Ni_0.3Sb₁₂ sample, compared to ZT=0.06 for the Yb_0.25Co₄Sb₁₂ sample at same temperature. This work indicates a strategy to improve the thermoelectric performance by Ni substitution of Co sites in the Yb_0.25Co₄Sb₁₂ skutterudite through simultaneous improvement of its electrical conductivity, Seebeck coefficient and reduction of its thermal conductivity.