Transverse Thermoelectric Transport in Polycrystalline NbP

The Nernst effect is a thermoelectric phenomenon which occurs upon the application of a temperature gradient and a perpendicular magnetic field, resulting in a mutually orthogonal output voltage. It is especially pronounced in Weyl semimetals due to their topological band structure, resulting in high-mobility two-carrier systems. Remarkably, for single-crystal NbP, the maximum Nernst thermopower exceeds 800 mV K-1 at 109 K in a magnetic field of 9 T [1]. In published work, polycrystalline NbP with an average grainsize of ~100 microns retains a large Nernst thermopower, although it is decreased by a factor of ~8 at a similar magnetic field and temperature [2]. In an attempt to further explore the efficiency of transverse thermoelectric transport properties in connection to the grain size of polycrystalline NbP, a group of polycrystalline NbP samples are annealed for different lengths of time to produce various grain sizes. Here, transport properties are presented for a polycrystalline sample of NbP annealed for approximately one week at 1000°C.
[1] S. J. Watzman et al. Phys. Rev. B 97(16), 161404(R) (2018).
[2] C. Fu et al. Energy Environ. Sci. 11(10), 2813-2830 (2018).