M. Sergent

Sur de nouvelles phases séléniées ternaires du molybdène

Abstract The synthesis and the crystal properties of new selenides of formula MxMo3Se4 are described. If M = Zn, Ag, Cd, Sn and Pb, they are stoichiometric with x = 0.6; if M = Fe, Mn, Cr, V, Ti, triclinic solid solutions are observed with 0.5

Superconducting Chevrel phases: prospects and perspectives

Abstract Research on superconducting Chevrel phases and other properties is reviewed: the impact of this large family of compounds on solid-state cluster chemistry, their novel pseudo-molecular structures with a new manner of coupling the clusters producing some outstanding physical properties: ternary superconductors, high Tc and Hc2 superconductors, interplay between superconductivity and long-range magnetic order, magnetic-field induced superconductivity and potential developement of superconducting wires are described; the electron donor-acceptor role of the Mo6 cluster and cation donor-acceptor role of the channels of the structure of the quasi rigid Mo6X8 building blocks provide potential for cationic electrodes for secondary batteries.

New pseudo-one-dimensional metals: M2Mo6Se6 (M = Na, In, K, TI), M2Mo6S6 (M = K, Rb, Cs), M2Mo6Te6 (M = In, TI)

Abstract We present a new series of ternary chalcogenides, derived from divalent molybdenum: M2Mo6X6. These compounds crystallize in a hexagonal lattice with a ≈ 9 A, c ≈ 4.5 A, and space group P6 3 m . The compounds are characterized by clusters (Mo3)1∞ in the form of linear chains, resulting from a linear condensation of Mo6 octahedral clusters. The (Mo3)1∞ clusters are well separated from each other, with the shortest MoMo intercluster distance larger than 6 A. The resulting pseudo-one-dimensional structures show remarkable anisotropy of physical properties.

A study of the solid solutions PbyMo6X8−xX′x and Mo6X8−xX′x (X, X′ = S, Se, Te) and their superconducting properties

Abstract The solid solutions Pb y Mo 6 X 8−x X′ x and Mo 6 X 8−x X′ x (X, X′ = S, Se, Te) are studied and it is shown that there are correlations between T c and certain structural parameters.

New compounds of the type Mo2Re4X8 (M = S, Se) containing octahedral Mo2Re4 clusters

We report the preparation and some properties of new compounds with the composition Mo2Re4X8 (X = S, Se) and Mo4Re2Te8. These compounds are isostructural to Mo6Se8 and present mixed octahedral clusters : Mo2Re4 or Mo4Re2. The solid solutions Mo2Re4S8−xSex (0 ⩽ x ⩽ 8) and Mo2Re4Se8−xTex (0 ⩽ x ⩽ 1.2) are semiconducting, whereas Mo4Re2Te8 is metallic and becomes superconducting at Tc = 3.55 K.

Ternary molybdenum chalcogenides: a route to new extended clusters

Within the last decade, the ternary molybdenum chalcogenides have played a major role in superconductivity: opening of the ternary superconductor range, competition between superconductivity and magnetism. It is mainly due to the pseudomolecular nature of the Mo 6 X 8 unit. In these materials, the Mo 6 cluster plays the electron-acceptor role and the number of valence electrons per molybdenum atom is related to the Mo-Mo intracluster bonding. The increase of this valence electron concentration (VEC) per molybdenum in new ternary chalcogenides corresponds to larger and larger clusters. These new extended clusters belong to a very large family containing the general Mo 3n X 3n+2 ( n ≥2) block unit. The tridimensional stacking of these building blocks provides more and more large channels and leads to a more and more anisotropic character of their physical properties.

A new pseudo-one-dimensional superconductor: Tℓ2Mo6Se6

Abstract The properties of a new superconducting pseudo-one-dimensional compound, Tl2Mo6Se6 are presented. The crystal structure of this material contains linear chains in the form of infinite stacks of Mo6 clusters. The anisotropy in the normal state resistivity is found to be of the order of 103 and the parallel upper critical field is 26 times higher than the perpendicular one.

Rare earth based chevrel phases REMo6X8: Crystal growth, physical and superconducting properties

Etude des proprietes magnetiques a basse temperature des phases de Chevrel. Interaction entre supraconductivite et magnetisme

Synthesis and electrical properties of new chalcogenide compounds containing mixed (Mo, Me)6 octahedral clusters (Me = Ru or Rh)

Abstract We report the synthesis and some properties of new compounds and some solid solutions containing mixed octahedral ( Me ) 6 clusters ( Me = Mo, Ru, Rh). The compound Mo 4 Ru 2 Se 8 is semiconducting whereas the limit compounds Mo 4 Ru 2 Te 8 and Mo 4.66 Rh 1.33 Te 8 are metallic. Superconductivity was found around the composition Mo 5 RuTe 8 .

Magnetic relaxation effects in PbMo6S8 superconducting single crystals: A comparison with high-Tc superconductors

Abstract Magnetic measurements performed on PbMo6S8 single crystals show that this classic isotropic superconductor (Tc = 14.5 K) presents surprisingly similar irreversibility and relaxation properties as those generally attributed to layered high-Tc superconductors. An irreversibility line H ∗ = H ∗ 0 (1-t) m with m∼ 3 2 is observed for H ⪅ 1 kOe. From the magnetic relaxation rates measured below this irreversibility line, activation energies U0 around 15 meV are derived within the flux creep picture. The similarity with the high-Tc oxides is explained by the very short coherence length ξ ≈ 25 A of PbMo6S8 which also makes this compound sensitive to disorder and local defects.