Charge transfer associated with lithium insertion in Mo1-yNbyS2 layered compounds
The Mo1--yNbyS2 layered compounds form solid solutions. the coordination of the Mo and Nb atoms by S atoms is trigonal prismatic over the entire range of composition, o <y<1.The dz2 band, separated from the other d-bands by a bandgap of the order of 1 eV, contains y empty states per formula unit. For y< 0.6, Li/LixMo1-yNbyS electrochemical cells reveal a sharp voltage drop of V(x) at a critical composition x which is correlated to y by xc=y. This result clearly establishes the transfer of one electron per intercalated lithium (x<0.6) to the dz2 band of the host. Electrochemical cells, made with samples whose X-ray diffraction spectra suggest the presence of structural disorder in the host lattice, show a less abrupt voltage drop near xc, in qualitative agreement with the influence of disorder on the electronic density-of-states distribution N(E) near a band edge. The origin of the voltage drop observed for LixMo0.2Nb0.8S2 is not fully established.