Unusual Behaviors in Electrical Conductivity of Phenanthrene Crystal

Abstract

Abstract Two kinds of unusual behavior in the temperature dependence of electrical conductivity has been observed. One is the anomaly that the resistance begins to increase remarkably with the rise in the temperature around 64°C; the other is a bending-phenomenon in the linear temperature-dependence of the resistance about 54°C. The observed activation energies for conduction are 3.0–3.3 eV below and 4.5–4.8 eV above the anomaly, the energies of which are almost compatible with the intrinsic band-gap energies for conduction, 3.5 and 4.6 eV, estimated, respectively, from the optical absorption and from the values of the ionization potential and the electron affinity. As for below the bending-phenomenon, the observed activation energy is 1.4–1.6 eV, which is quite small compared with the intrinsic band-gap energies estimated. The anomaly beginning around 64°C is interpreted as due to the crystal-phase transition of a higher-order at 60–70°C; the remarkable increase in resistance may be connected with the changes in the intermolecular interaction in the crystal due to the rearrangement of molecules caused by the phase transition. The bending-phenomenon at about 54°C seems to be attributable to an impurity-effect by oxygen.