STRUCTURE AND ELECTRICAL-PROPERTIES OF AU2S

A gold compound Au2S was prepared from K[Au(CN)(2)] and H2S and some physico-chemical properties of the product were examined, that is, X-ray powder diffraction (80-450 K), TG-DTA (300-620 K), DSC (110-300 K), electrical conductivity (150-370 K), thermoelectromotive force (EMF) (210-420 K), and the gold ionic transport number (343, 393 K). The sulfide Au2S was a cuprite-type compound with the space group Pn3m (80-620 K) and the lattice spacing a = 502.057 pm (300 K). The sulfide decomposed to Au and S under an inert atmosphere or Au and SO2 in air over 490 K. The sulfide was a p-type semiconductor with sigma(300 K)=10(-5) Scm(-1) and E(a)(300-370 K)=0.37 eV. The conductivity of Au2S was successfully expressed by the relation sigma=sigma(0)exp (-T--1/4). The absolute Seebeck coefficient of Au2S did not appreciably change with temperature and was about 700 mu V K-1. The random-range hopping model was applicable to the case of Au2S. The gold ionic transport numbers of Au2S at 343 and 393 K by the Tubandt method were negligibly small.