Topotactic Intercalation of a Metallic Dense Host Matrix Chalcogenide with Large Electron−Phonon Coupling: Crystal Structures and Electronic Properties of LixMo2SbS2 (0 ≤ x < 0.7)

Abstract

The functionality of the three-dimensional ternary chalcogenide Mo2SbS2 as a host is demonstrated by low-temperature reactions involving lithium-metal−liquid-ammonia reducing solutions. Rietveld analysis of neutron (T = 1.5 and 270 K) and synchrotron X-ray (T = 300 K) powder diffraction data proves that topotactic insertion of lithium in quasi-one-dimensional channels produces an isostructural family of LixMo2SbS2 (0 ≤ x < 0.7) compounds. The optimization of the electronic properties of such a dense host matrix material via intercalation is studied by band structure calculations using the density functional theory (DFT). Mulliken population analysis indicates that a major effect of the presence of Li in the Mo2SbS2 is the filling of the d-holes close to Fermi level and therefore only the p-orbitals give rise to mobile carriers in the LixMo2SbS2. Charge disproportionation at the two Mo nonequivalent crystallographic sites and the favorable electrostatic environment of the Li (which is partially depleted of its charge) point to polaron formation, consistent with partial localization upon Li-doping. The resistivity, ρ(T) (2 ≤ T ≤ 270 K), for all compositions studied is modeled by the Bloch−Gruneisen function. Phenomenologically, a percolation model describes the crossover of ρ(T) to a higher conductivity regime at a critical Li composition of xc ≈ 0.19. As reflected in the small overall modification to its electronic conductivity, the host efficiently accommodates the perturbations due to chemical and physical (P ≤ 17 kbar) pressure. The data analysis finds an enhanced electron−phonon coupling constant for Mo2SbS2 (λt ≈ 2.45) on the basis of the one-electron band-theory model.