The effects of bismuth intercalation on structure and thermal conductivity of TiS2

The structure and thermal conductivity of the bismuth (Bi) intercalated compounds BixTiS2 (0 ≤ x ≤ 0.25) were investigated by using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and thermal conductivity measurements. The results indicated that besides lattice expansion and distortion, bismuth intercalation caused structural transition of BixTiS2 from stage-1 to stage-2 as x ≥ ∼0.1, which led to the appearance of D4 and A2 modes in Raman spectra. The enhancement of relative intensities of D4 and A2 peaks with increasing Bi content reflected increase of the concentration of stage-2 phase in the samples. The red shift of mode Eg as well as D4 and A2 would reflect weakening of intra-layer bonds, while the blue shift of A1g after intercalation suggested the enhancement of chemical binding in the van der Waals gaps due to charge transfer. In addition, the weakening of A1g intensity can be explained by the lattice distortion produced by bismuth intercalation. Remarkable reduction in (lattice) thermal conductivity of titanium disulfide (TiS2) through Bi intercalation was realized, which could be attributed to the phonon scattering by “rattling” of the intercalated bismuth atoms in the van der Waals gaps of TiS2.