ELECTRONIC-STRUCTURE AND MAGNETIC-PROPERTIES OF NONSTOICHIOMETRIC TLXV5S8 - THE INFLUENCE OF TL CONTENT

Ultraviolet photoelectron spectroscopy (UPS) reveals that Tl0.97V5S8 a nd Tl0.51V5S8 are metals. The density of states at the Fermi level is higher in the Tl-rich compound. The well resolved conduction band is s ignificantly smaller in Tl0.51V5S8 and is mainly composed of V d-state s. The broad valence band is composed of S 3p and V 3d states with a b roadening due to the hybridization with Tl 6s and 6p states. The Tl at oms as well as the V atoms carry a low formal positive charge and the bonding interactions between the guest Tl and the V5S8 host matrix is highly covalent. Magnetic susceptibility measurements show a different behaviour for Tl-rich and Tl-poor samples, respectively. The changes of the magnetic properties with decreasing Tl content are attributed t o changes of the crystal structure.