Microstructural modification of Co₄Sb₁₂ skutterudite thermoelectric material through Al exceed doping

Thermoelectric (TE) materials are functional materials which could be used to achieve direct conversion between thermal and electric energy. Skutterudite materials have shown promise in the field of thermoelectric materials for the application within the medium temperature range of 200 to 500 °C. In this work, excess doping of Al into Co₄Sb₁₂ was investigated to examine their effect on the skutterudite morphology and ultimately the thermoelectric performance. Fully dense samples of Al_xCo₄Sb₁₂ skutterudite (x = 0.3, 0.6, 2) were obtained; using mechanical alloying technique (MA) followed by spark plasma sintering process (SPS). The XRD result showed that the Al-addition resulted in the formation of a skutterudite phase associated with AlSb as a secondary phase. However, EDX indicated islands of a skutterudite phase surrounded by Al-rich spots located in the grain boundaries. Moreover, the addition of Al had a significant effect on the lattice thermal conductivity of Co₄Sb₁₂, which was reduced by ~45% in the case of x =2. It is believed that grain boundary phonon scattering plays a key role in reducing the thermal conductivity. However, a low figure of merit ZT was obtained as a consequence of a high electrical resistivity. Thus, this work is useful in deriving a pathway for improvement in thermoelectrics through microstructural modification.