Showing papers by "S. Chandrasekhar published in 1999"

Quasi-one dimensional electrical conductivity and thermoelectric power studies on a discotic liquid crystal

Abstract: We have studied the electrical conductivity of well aligned samples of hexahexylthiotriphenylene (HHTT) in the pure as well as doped states. The dopant used was a small concentration (0.62 mole %) of the electron acceptor trinitrofluorenone (TNF). In the columnar phases, doping causes the AC(1 kHz) conductivity along the columnar axis (σ ‖) to increase by a factor of 107 or more relative to that in undoped samples; σ ‖ attains a value of 10−2S/m, which was the maximum measurable limit of our experimental set up. On the other hand, in the isotropic phase doping makes hardly any difference to the conductivity. The frequency dependence of the conductivity has been investigated. The DC conductivity of doped samples exhibits an enormous anisotropy, σ ‖/σ ⊥ ≥ 1010, which is 7 orders higher than that reported for any liquid crystalline system, and, to our knowledge, the largest observed in an organic conductor. We also report the first thermoelectric power studies on these ‘molecular wires’. The sign of the thermoelectric power is in conformity with the expected nature of the charge carriers, namely, holes.

Recent developments in discotic liquid crystals

Abstract: After a brief introduction to discotic liquid crystals, we describe recent progress in elucidating the properties of the columnar phases as one-dimensional electrical conductors (or molecular wires), fast photoconductors, light emitting diodes and ferroelectrics, all of which have potentially important practical applications.