LiMo₈O₁₀: Polar Crystal Structure with Infinite Edge-Sharing Molybdenum Octahedra

Polycrystalline LiMo₈O₁₀ was prepared in a sealed Mo crucible at 1380 °C for 48 h using the conventional high-temperature solid-state method. The polar tetragonal crystal structure (space group I4₁md) is confirmed based on the Rietveld refinement of powder neutron diffraction and ⁷Li/⁶Li solid-state NMR. The crystal structure features infinite chains of Mo₄O₅ (i.e., Mo₂Mo_4/2O_6/2O_6/3) as a repeat unit containing edge-sharing Mo₆ octahedra with strong Mo-Mo metal bonding along the chain. X-ray absorption near-edge spectroscopy of the Mo-L₃ edge is consistent with the formal Mo valence/configuration. Magnetic measurements reveal that LiMo₈O₁₀ is paramagnetic down to 1.8 K. Temperature-dependent resistivity [ρ(T)] measurement indicates a semiconducting behavior that can be fitted with Mott's variable range hopping conduction mechanism in the temperature range of 215 and 45 K. The ρ(T) curve exhibits an exponential increase below 5 K with a large ratio of ρ_1.8/ρ₃₀₀ = 435. LiMo₈O₁₀ shows a negative field-dependent magnetoresistance between 2 and 25 K. Heat capacity measurement fitted with the modified Debye model yields the Debye temperature of 365 K.