Tl_0.6Mo₃S₅, an original large tunnel-like molybdenum sulfide with Mo zigzag chains and disordered Tl cations

Patrick Gougeon (1) , Philippe Gall (1) , Sylvie Migot (2) , Jaafar M Ghanbaja (2) , Maryvonne Hervieu (3) , Petr Levinsky (4) , Anne Dauscher (2) , Bernard Malaman (2) , Bertrand Lenoir (2) , Christophe Candolfi (2)

1 ISCR - Institut des Sciences Chimiques de Rennes
2 IJL - Institut Jean Lamour
3 CRISMAT - Laboratoire de cristallographie et sciences des matériaux
4 FZU / CAS - Institute of Physics of the Czech Academy of Sciences

We report on the crystal structure and physical properties of Tl_0.6Mo₃S₅, which belongs to a novel family of materials with large tunnels, reminiscent of those observed in the romanechite structure type. Tl cations are partially filling these tunnels delimited by the Mo-S cluster framework in which the Mo atoms form infinite zigzag chains. Single-crystal X-ray diffraction data indicate that this compound crystallizes in the monoclinic, non-centrosymmetric space group P2₁ (no. 4; a = 9.344(2) angstrom, b = 3.234(2) A, c = 11.669(2) A and beta = 113.09(2)° at 293 K). While electron diffraction performed on single crystals further evidences a commensurate modulation running solely along the b axis with a modulation wave vector further experiments carried out on a polycrystalline sample suggest a compositional dependence of q on the Tl content. Low-temperature transport properties measurements (5-300 K) reveal that Tl_0.6Mo₃S₅ behaves as a narrow-band-gap n-type semiconductor. The strongly non-linear temperature dependence of the thermopower further suggests the presence of several electronic bands contributing to the electrical transport. Consistent with the extended electronic distribution in the tunnels that requires a description using two adjacent Tl sites, specific heat data measured down to 0.35 K evidence the presence of a Schottky-type anomaly that may be associated with the tunneling of the Tl cations between several equivalent, off-centered equilibrium sites. This inherent disorder contributes to suppression of the low-temperature Umklapp peak in the lattice thermal conductivity k_L, the temperature dependence of which mimics that observed in strongly-disordered compounds. In spite of this characteristic, high k_L values of up to 3.8 W m^-1K^-1 are reached at 300 K, due to the covalent Mo-S network that contributes to maintaining high sound velocities.

Domaines: Matériaux; Chimie inorganique

Patrick Gougeon, Philippe Gall, Sylvie Migot, Jaafar M Ghanbaja, Maryvonne Hervieu, et al.. Tl_0.6Mo₃S₅, an original large tunnel-like molybdenum sulfide with Mo zigzag chains and disordered Tl cations. Materials Advances, 2021, 2 (18), pp.6020-6030. ⟨10.1039/d1ma00568e⟩. ⟨hal-03367738⟩