New Publication.


Sejung Ahn, Honam Yoo,Youngwoo Nam, Jihyun Park, Yukyung Kim, Mikyong Yoo, Chongsu Cho and Yungwoo Park, " Temperature dependent conductivity and thermoelectric power of the iodine doped poly(vinyl alcohol)-Cu2+ chelate ", Synth. Met. 159, 2086-2090 (2009) [pdf]

Abstract.

We have investigated the temperature dependence of electrical conductivity and thermoelectric power
(TEP) at 1.7 K < T < 300 K in an organo metallic complex, the iodine doped poly(vinyl alcohol)–Cu2+
chelate. We observed intrinsic metallic temperature dependence of resistivity from room temperature
to 68K with a broad minimum [ρ(68 K)/ρ(300 K) ∼0.75], which has not been observed previously in
similar organo metallic complexes. There occurs an unusual metal-insulator transition at T ∼68K and
the resisitivity increases upon cooling below 68 K. However, the low temperature resistivity becomes
finite (instead of going to infinity), [ρ(1.7 K)/ρ(300 K) ∼0.98] indicating that a quantum mechanical
tunneling conduction is dominant at this low temperature. It is remarkable that the resistivity at
1.7 K is as small as that of room temperature. Such unusual temperature dependence of conductivity
could be understood as thermally assisted hopping conduction between metallic islands. However,
the observed intrinsic metallic temperature dependence of resistivity implies that such hopping conduction
barrier is not important at high temperature (T > 68 K). The intrinsic metallic characteristics
are confirmed by the quasi-linear temperature dependence of TEP for the whole measured temperature
range (1.7 K< T < 300 K) with a small slope change at low temperature, T < 68K, which is
understood as an effect of variable range hopping (VRH) conduction at low temperature. The results
of magneto resistance (MR) and magneto thermoelectric power (MTEP) are consistent with the above
interpretation.
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http://ntl.snu.ac.kr/438