Single-Crystal Studies of the Chevrel-Phase Superconductor LaxMo6Se8: I: Correlation betweenTcand the Interatomic Distances

✍ Scribed by F. Le Berre; O. Peña; C. Perrin; M. Sergent; R. Horyń; A. Wojakowski

• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 366 KB
• Volume: 136
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7663

✦ Synopsis

We report, for the first time in the literature, crystal structure studies of rare-earth-based Chevrel-phase selenides of formulae LaxMo 6 Se 8 with variable contents (x) of lanthanum. Single crystals were grown from off-stoichiometric mixtures that had been melted and slowly cooled from about 1675°°C. The origin site of the rhombohedral lattice may present a considerable deficiency in the lanthanum occupancy, whereas no vacancies were found in the Mo 6 Se 8 sublattice. The superconducting temperature of this phase depends strongly on the lanthanum concentration, as we previously reported for powder samples. From the crystal structure data obtained for three crystals with different lanthanum contents, a clear correlation was established between T c and the lanthanum occupancy at the origin site. The critical temperature varied from 9.4 to 11.0 K for x ‫؍‬ 0.839(2) to x ‫؍‬ 0.9412(2), respectively, the lanthanum contents being derived from structural data taken on the same single crystals. Lattice constants, positional parameters, and interatomic distances are presented, and their respective variations are discussed in terms of geometrical effects and charge transfer phenomena. A full comparison is made with the corresponding rare-earth molybdenum sulfides REMo 6 S 8 . Basic physical properties, i.e., electrical resistivity, ac susceptibility, and dc magnetization, are presented in an accompanying paper; they confirm that LaMo 6 Se 8 is an extremely high-field superconductor.