SINGLE-CRYSTAL STRUCTURE, MAGNETIC-PROPERTIES, AND ELECTRONIC-STRUCTURE OF TLXCR5S8 (X=1.0 AND 0.7)

TlCr5S8 is isotypic with TlV5S8. It consists of layers of edge sharing CrS6-octahedra connected by other CrS6-octahedra to a three-dimension al network. The distances within the two-dimensional metal atom networ k are irregularly distributed with one short (2.959 angstrom) and two longer (3.332 and 3.339 angstrom) separations between neighboring Cr a toms. The environment of the Tl atoms within the rectangular channels is highly asymmetric and may be described as a 4 + 6 coordination. Mag netic susceptibility measurements show maxima of the susceptibility at about 125 and 145 K for the Tl-rich and Tl-poor samples, respectively . The shape of the susceptibility maxima is atypical and points to a c omplex interaction of the magnetic moments. Ultraviolet photoelectron spectroscopy (UPS) reveals that TlCr5S8 is a semiconductor. The valenc e band is composed of S 3p and Cr 3d states with a broadening due to t he hybridization with Tl 6s and 6p states. The Tl atoms as well as the Cr atoms carry a low formal positive charge and the interactions betw een the guest Tl and the Cr5S8 host matrix are highly covalent. (C) 19 94 Academic Press, Inc.