dc conductivity of tetrathiofulvalene bromide (TTF−Brn) and TTF-Insingle crystals

Abstract

Tetrathiofulvalene (TTF) combines with the halogens to form crystals with interesting electrical properties due to the segregated stacking of the TTF molecules. The monoclinic forms of TTF-${\mathrm{I}}_n$ and TTF-${\mathrm{Br}}_n$ ($n\sim 0.7$) have a high conductivity [100-550 ${\left(\mathrm{\Omega }\mathrm{c}\mathrm{m}\right)}^{-1\mathrm{}}$] which is almost temperature independent for a very broad region near room temperature but display a thermally activated conductivity at low temperature. Unlike monoclinic TTF-${\mathrm{Br}}_n$, monoclinic TTF-${\mathrm{I}}_n$ displays a strong hysteresis in its conductivity upon temperature cycling. The conductivity of the orthorhombic form of TTF-${\mathrm{I}}_n$ ($n=2\mathrm{}$) is about five orders of magnitude lower than the monoclinic form at room temperature and is thermally activated over the entire temperature range.