Kigook Song, Robert D. Miller, et al.
Macromolecules
We report results of electrical-conductivity, thermoelectric-power, and optical experiments on single crystals of Ni1-xCoxS2 (0x0.12). The results cannot be explained by means of a conventional one-electron model. However, if it is assumed that both strong electronic correlations and strong electron-phonon coupling exists for electrons in the narrow d bands associated with the transition-metal cations, the experimental results can be understood quantitatively. In the model presented, NiS2 is a Mott insulator, in which the gap is due to a correlation splitting of the 3d-eg band. The introduction of Co substitutionally for Ni results in one hole per Co atom in the lower of these bands. However, strong electron-phonon coupling leads to small-polaron formation, and thus a drastic band narrowing with increasing temperature. For this range of x, the d-band holes conduct only by means of thermally activated hopping for temperatures above 100 K. Screening effects due to thermally excited carriers lead to a collapse of the energy gap at a critical temperature, but small-polaron hopping remains the predominant conduction mechanism. © 1980 The American Physical Society.
Kigook Song, Robert D. Miller, et al.
Macromolecules
Thomas E. Karis, C. Mark Seymour, et al.
Rheologica Acta
David B. Mitzi
Journal of Materials Chemistry
Corneliu Constantinescu
SPIE Optical Engineering + Applications 2009