The Chevrel-phase PbMo6S8 has a value of Hc2(0) of about 60 teslas (600 kilogauss), the largest value observed for any material prior to 1986. Chevrel phase compounds. The diversity of structures of catenated sulfur is also seen in the structures of the polysulfur cations or anions resulting from the redox reactions of the catenated species. Being molecular, they dissolve well in organic solvents, such as CS2. What does Chevra mean? A series of ternary molybdenum chalcogenide compounds. Several of the Chevrel-phase compounds have relatively high values of Tc, the maximum being about 15 K (−433°F) for PbMo6S8. A spoken definition of Chevrel phase. A number of Chevrel-phase compounds of the form RMo6X8, where R is a rare-earth element with a partially filled 4f electron shell and X is S or Se, display magnetic order at low temperatures in addition to superconductivity. The cluster units are connected 3-dimensionally (Figure $$\PageIndex{20}$$). and their structures determined. MoS2 is used as a solid lubricant added to gasoline, and also as a catalyst for hydrogenation reactions. The highest Hc2(0) that had been previously reported for a non-Chevrel-phase material was 40 teslas (400 kilogauss) for the A15 compound Nb3Ge. Missed the LibreFest? 104.232.27.237 The compounds have the general formula M x Mo 6 X 8, where M represents any one of a large number (nearly 40) of metallic elements throughout the periodic table; x has values between 1 and 4, depending on the M element; and X is a chalcogen (sulfur, selenium or tellurium). Cookies help us deliver our services. For more information contact us at [email protected] or check out our status page at https://status.libretexts.org. Prior to 1986, the highest Tc of any known material was 23 K (−418°F) for the A15 compound Nb3Ge. creative writing lost in the jungle; simulation homework help; creative narrative writing. Maple, M. Brian Department of Physics, University of California, San Diego, California. They were reported by R. Chevrel, M. Sergent, and J. Prigent in 1971. Because the electronegativity of sulfur ($$\chi$$ = 2.58) is much smaller than that of oxygen ($$\chi$$ = 3.44) and sulfur is a soft element, the ionicity in the bonds of sulfur compounds is low and hydrogen bonding is not important. The LibreTexts libraries are Powered by MindTouch® and are supported by the Department of Education Open Textbook Pilot Project, the UC Davis Office of the Provost, the UC Davis Library, the California State University Affordable Learning Solutions Program, and Merlot. european studies essay. Catenation is the bonding between the same chalcogen atoms, and both simple substances and ions of chalcogens take a variety of structures. Copyright © McGraw-Hill Global Education Holdings, LLC. Although it has long been recognized that solutions of chalcogen elements in sulfuric acid showed beautiful blue, red, and yellow colors, the polycationic species that give rise to these colors, S42+, S62+, S64+, S82+, S102+, S192+, or those of other chalcogen atoms, have been isolated by the reaction with AsF5, etc. L. Pauling determined the structure of MoS2 in 1923. essay questions for glass castle. There is only one crystalline form of tellurium, which is a spiral chain polymer that shows electric conductivity. This information should not be considered complete, up to date, and is not intended to be used in place of a visit, consultation, or advice of a legal, medical, or any other professional. Sulfur, selenium, and tellurium are called chalcogens. For example, unlike neutral S8, S82+ takes a cyclic structure that has a weak coupling interaction between two transannular sulfur atoms (Figure $$\PageIndex{18}$$). One of these structures, that of PbMo6S8, is shown in the illustration. Black selenium, which is a complicated polymer, is also abundant. Tellurium also has eight stable isotopes and an atomic weight of 127.60+0.03. Information and translations of Chevra in the most comprehensive dictionary definitions … There are superconducting compounds called Chevrel phases which are important examples of the chalcogenide compounds of molybdenum. The problem has many phases. See also: A15 phases. We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. he general formula is described by M x Mo 6 X 8 (M = Pb, Sn, and Cu; X = S, Se, and Te), and six molybdenum atoms form a regular octahedral cluster, and eight chalcogenide atoms cap the eight triangular faces of the cluster.