Preparation, thermal stability and electrical transport properties of vaesite, NiS 2

Abstract

Vaesite, a nickel chalcogenide with NiS 2 formula, has been synthetized and studied by theoretical and experimental methods. NiS 2 was prepared by solid-state reaction under vacuum and densified by hot-pressing, at different consolidation conditions. Dense single-phase pellets (relative densities >94%) were obtained, without significant lattice distortions for different hot-pressing conditions. The thermal stability of NiS 2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS 2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni 1-x S (<1%vol), due to the strong desulfurization at T > 340 °C. The electronic band structure and density of states were calculated by Density Functional Theory (DFT), indicating a metallic behavior. However, the electronic transport measurements showed p-type semiconductivity for bulk NiS 2 , verifying its characteristic behavior has a Mott insulator. The consolidation conditions strongly influence the electronic properties, with the best room-temperature Seebeck coefficient, electrical resistivity and power factor being 182 µVK −1 , 2,257 µΩ m and 14.1 µWK −2 m −1 , respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.