Preparation, thermal stability and electrical transport properties of vaesite, NiS₂

Abstract

Vaesite, a nickel chalcogenide with NiS2 formula, has been synthetized and studied by theoretical and experimental methods. NiS2 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 NiS2 was studied by thermogravimetric analysis. Both as-synthetized and hot-pressed NiS2 have a single phase nature, although some hot-pressed samples had traces of the sulfur deficient phase, Ni1-xS (<1%vol), due to the strong desulfurization at T > 340ºC. 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 NiS2, 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 182µVK-1, 2257μΩm and 14.1µWK-2m-1, respectively, pointing this compound as a good starting point for a new family of thermoelectric materials.

Tetrahedrite-(Ni), Cu6(Cu4Ni2)Sb4S13, the first nickel member of tetrahedrite group mineral from Luobusa chromite deposits, Tibet, China

“…phases at a temperature above 340 °C (Ferreira et al 2019). In this study, we didn't find millerite-bearing composite inclusions with tetrahedrite-(Ni).…”