A giant Nernst power factor and figure-of-merit in polycrystalline NbSb2 for Ettingshausen refrigeration

Abstract

Ettingshausen refrigeration is a promising solid-state refrigeration technology that can be used in exploring the quantum state of matters and superconducting materials, but its development is greatly limited by the lack of high-performance polycrystalline thermomagnetic materials. In this work, we report that the polycrystalline topological semimetal NbSb₂ has a giant Nernst power factor ((PF)_N) of 1269 × 10⁻⁴ W m⁻¹ K⁻² under 9 T at 28 K and a Nernst figure-of-merit (z_N) of 28.5 × 10⁻⁴ K⁻¹ under 9 T at 18 K, both of which are record-high values among the polycrystalline thermomagnetic materials. The observed high thermomagnetic performance is mainly attributed to the large and unsaturated Nernst thermopower under a high magnetic field. Due to the diminished anisotropy, the polycrystalline NbSb₂ has similar high carrier mobility to the single-crystalline NbSb₂ in the bc-plane, yielding large Nernst thermopower in low temperature ranges. Combining the excellent thermomagnetic performance and low-cost and time-saving fabrication process, polycrystalline NbSb₂ is a very competitive candidate material for Ettingshausen refrigeration.