Quasi-one
dimensional electrical conductivity and thermoelectric
power
studies on a discotic liquid crystal
V S K BALAGURUSAMY, S KRISHNA PRASAD, S
CHANDRASEKHAR*, SANDEEP KUMAR, M MANICKAM and C V
YELAMAGGAD
Centre for Liquid Crystal
Research, P.B. No. 1329, Jalahalli, Bangalore 560 013,
India
*Also at Jawaharlal Nehru
Centre for Advanced Scientific Research, Bangalore 560
064, India
Abstract:
We have studied the
electrical conductivity of well aligned samples
of hexahexylthio-triphenylene (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 (s ê ï ) to
increase by a factor of 10 7 or more relative to
that in undoped samples; s ï ï
attains a value of 10 -2 S/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, s ï ï / s ^ ³ 10
10 , 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.
Keywords. Quasi-one
dimensional conductivity; thermoelectric power;
discotic liquid crystals.
PACS Nos 61.30.Gd;
73.50.Lw
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