Improved Thermoelectric Properties of YbCo₂Zn₂₀ through Ni Doping

As global energy demands escalate and environmental concerns intensify, thermoelectricity emerges as a sustainable and innovative solution for harnessing waste heat and reducing our ecological footprint. While there are now a variety of effective high-temperature thermoelectrics, those that are useful at low temperatures are less common. To address this, we focus on the heavy-fermion compounds YbTM₂Zn₂₀ (TM = Co, Rh, Ir), which previously were shown to exhibit attractive thermoelectric figures of merit at low temperatures [1,2]. In particular, we present an investigation on the chemical substitution series YbCo_2-xNi_xZn₂₀, where we find that modest Ni doping rapidly increases the low-temperature Seebeck coefficient. As a result, the thermoelectric figure of merit is also improved. This is compared to what is seen for Co→Rh→Ir tuning, which also results in a rapid enhancement of the Seebeck coefficient. By comparing the distinct tuning axes of isoelectronic volume expansion (Co → Ir) and isovolume electronic tuning (Co → Ni) using magnetization, heat capacity, electrical resistivity, and Hall effect measurements, we clarify strategies for optimizing the thermoelectric properties of these materials and provide insights into the f-electron ground state.



[1] Mun et al., Phys. Rev. B 86, 115110 (2012).

[2] Wei, et. al. Sci. Adv. 5, eaaw6183 (2019).