The effect of temperature on libron frequencies in molecular crystals: Implications for TTF-TCNQ

Abstract

Results for the effect of pressure and oemperature on lattice-phonon frequencies in six crystals (As 4S 4, S 8, S 4N 4, C 10H 8, C 14H 10, C 16H 10) have been analyzed to separate the phonon-excitation-driven (“explicit”) and the thermal-expansion-driven (“implicit”) contributions to d v/d T. The data establish that the volume-driven implicit effect dominates the temperature dependence of external-mode frequencies in molecular crystals. This finding has a bearing upon recent proposals for the role of librons in the electron transport of TTF-TCNQ.