Transport and Thermoelectric Coefficients of the Co9S8 Metal: A Comparison with the Spin Polarized CoS2

A Co9S8 dense ceramic sintered by spark plasma sintering has been characterized by X-ray powder diffraction and transmission electron microscopy (diffraction and high resolution). This allowed magnetic, electronic, and thermal transport measurements to be made for a cubic (a = 9.927(2)angstrom) Co9S8 sample free of impurities and structural defects. The magnetic susceptibility and magnetic field dependence of the magnetization point toward an antiferromagnetic state, whereas the four-probe resistivity reveals a very metallic behavior with rho(300 K) = 80 mu Omega.cm described by a classical electron phonon model. When compared to CoS2, even if Co9S8 exhibits lower. values associated with the lack of ferromagnetic fluctuations existing in the former, the Co9S8 thermoelectric power factor, negative as in CoS2, is smaller, nonetheless leading to a power factor (PF) reaching PF approximate to 0.5 mW m(-1) K-2 at 300 K. In Co9S8, with its low rho going with a very high electronic part of the thermal conductivity., the lattice part of. is smaller than that of CoS2 (similar to 2 W m(-1) K-1 for Co9S8 at 300 K) suggesting that the more complex structure of Co9S8, with two different types of CoSn polyhedra, plays an important role.

Automated summary

A Co9S8 dense ceramic sintered by spark plasma sintering was characterized and studied for its magnetic, electronic, and thermal transport properties. The material exhibits antiferromagnetic behavior, metallic conductivity, relatively high thermal conductivity, and a moderate thermoelectric power factor. The complex structure of Co9S8, with two different types of CoSn polyhedra, plays a crucial role in its properties.