Abstract

The electrical properties and bonding in Ba 6Cu 12S 13S 27 are analyzed with the extended Hückel tight-binding method. Because the Fermi level crosses several bands, metallic properties could be expected for this material. The electrical conductivity measurements as well as diffuse reflectance spectrum show that Ba 6Cu 12S 13S 27 is a semiconductor with a band gap of 2.49 eV. The discrepancy between the theoretical and experimental electrical properties is attributed to a random distribution of the Cu and Fe atoms in the structure. © 1997 Elsevier Science Ltd.