SUPERCONDUCTING AND NORMAL-STATE PROPERTIES OF BARIUM TANTALUM SULFIDE

Two types of compound in BaTa2S5 were specified according to their physical properties and superlattice arrangements. Electrical resistivity and ac magnetic susceptibility measurements indicate that both compounds are superconducting with transition temperatures T-c = 2.88 or 3.14 K, respectively, being dependent on formation processes of the specimens. The normal state properties, such as resistivity, Hall coefficient, magnetoresistance, and magnetic susceptibility, are also different between the two types of compound. Especially, magnetic susceptibility for the one type with lower T-c shows a Curie-Weiss-type paramagnetism below about 50 K, while that with higher T-c shows a temperature independent paramagnetism with a clear cusp at 70 K. Electron diffraction experiments show that the superlattice of the former compound is a root 28 x a root 28 x nc, while the structure of the latter consists of two types of superlattice which stack alternatively along the c axis. (C) 1995 Academic Press, Inc.