Journal of Chemical Physics, Vol.103, No.13, 5735-5741, 1995
Correlated Reflection and Conductivity Measurements on (2,5-Dimethyl-Dicyanoquinonediimine)(2)Cu Crystals and Films
We present correlated temperature dependent reflection and conductivity measurements on crystals and films of the undeuterated (h(g)) and the partly deuterated (d(6)) (2,5-dimethyldicyanoquinonediimine)(2)Cu radical anion salt. Using thin optical fibers, it was possible to study individual needle like crystals of a diameter of only a few mu m. The temperature dependence of the reflectivity of single (d(6)) needles in the visible and the near-infrared region shows a "dip", which coincides with the phase transition in the conductivity. To interpret our data, we extended the commonly used models for the conductivity from Drude and Epstein, so that we are able to deal with reflection and conductivity in terms of one consistent model. For the (d(6)) films, a metal-insulator phase transition has been proved by reflection and conductivity. With the assumption of a broad distribution of different phase transition temperatures for the crystallites of the films, the observed spectra of films can also be treated with the model used for the crystals.