1. Transport property of the iodine doped
Poly(vinyl Alcohol)- Cu2+ Chelate
H. N. Yoo1 , J. H. Park1, Y. K. Kim1, Y. W. Nam1, S. W. Chu1, S. J. Ahn1, M. K. Yoo2, C. S. Cho2 and Y. W. Park1
1 Department of Physics and Astronomy & Nano Systems Institute–National Core Research Center, Seoul National University, Seoul , Korea
2 Department of Agricultural Biotechnology, Seoul National University, Seoul , Korea
To investigate transport property, we measured temperature dependence of conductivity from room temperature to T=1.7K. We explain temperature dependence of conductivity by heterogeneous model. The magnetoresistance (MR, Δρ/ρ) is positive and increased linearly as magnetic field increases up to 7 tesla. In view of strong localization, we considered variable range hopping type conduction at low temperature. In barrier region of heterogeneous model, 2 dimensional hopping process is dominant and has positive magnetoresistance at low temperature. Thermoelectric power (TEP) has been measured from room temperature down to 1.8K to identify charge of carrier. At room temperature, the TEP is +110µV/K and it decreases linearly upon cooling to T=1.8K. The positive TEP and high room temperature value indicate that the (PVA/Cu2+/I2) is p-type semiconducting. And yet, the linear temperature dependence of TEP suggests metallic characteristics of the sample. In addition the magneto TEP shows a slight reduction compared to the zero-field results indicating little influence of the magnetic field on the TEP.
Electron energy dispersion relation(π-band)
Phonon dispesion relation
Introduction
I-V Characteristics
Conductivity
Iodine doped PVA-Cu2+ Chelate (PVA/Cu2+/I2)
PVA/CuCl2/I2 (2K)
SEM image
Schematic Diagram of SEM Image
PVA
Cu core
(not seen in SEM image)
Iodine island
poly(vinyl alcohol)
Cu2+
Cu2+ chelate I2
Iodine doped
Results and Discussion of the Iodine Doped PVA-Cu2+ Chelate
Resistivity
1st term
quasi 1D metal conductivity
dominant at high temperature
metallic region of heterogeneous model
A. B. Kaiser, Synth. Met. 45, 183 (1991)
2nd term
2D variable range hopping (VRH)
dominant at low temperature
barrier region of heterogeneous model
G. T. Kim, et al., phys. Rev. B 58, (1998)
Thermoelectric Power (TEP)
Room temperature TEP is +110μV/K.
TEP is linear to temperature and has positive slope. This indicates PVA/Cu/I has metallic characteristic and hole is main carrier
There is slight reduction of TEP value under 50K
Thin and thick sample almost same temperature dependence of TEP. So we assume that transport is achieved at surface.
A= ±
B= ± 78717
C= ±
1st term
Metallic contribution (TEP is linear to temperature)
Dominant characteristic of TEP
A is positive => main carrier is hole.
The origin of hole is Iodine doping. When Iodine is doped, Iodine is ionized to I3- and I5-. So Iodine is hole donor.
2nd term
Semiconducting contribution or 2D Variable Range Hopping
B is negative => main carrier is electron.
2nd term is suppressed rapidly but not vanishes. => C is small
At room temperature, 2nd term is about 1/12 of 1st term
At low temperature, 2nd term is competitive with 1st term, this is the reason of slight suppression of TEP value under T=50K
MR is positive and increases linearly as magnetic field increases up to 7tesla.
Magnetic effect is suppressed as temperature increases.
VRH model can explain positive linear MR at low temperature.
Because Cu2+ is paramagnetic, magnitude of MR can be affected.
Because iodine islands have heavy ion, spin-orbit scattering would suppress MR.
Magneto resistance (MR, Δρ/ρ)
Magneto resistance
Magneto TEP
We applied 7 tesla magnetic field parallel to temperature gradient.
There is slight reduction of magneto TEP value.
When magnetic field is applied, system is ordered and entropy decrease. Because TEP is entropy per carrier, TEP values are decreased.
Summary
Iodine doped PVA-Cu2+ Chelate (PVA/Cu2+/I2) is a mixed system of both metal chelates and charge-transfer complexes.
Temperature dependence of resistivity can be explained by heterogeneous model and the magneto resistance is a consistent with the model of mixed system..
TEP of PVA/Cu/I follows heterogeneous model and there is slight reduction of magneto TEP and it is explained by magnetic ordering.
This work was supported by the Global Partnership Program (GPP) of KICOS through the Ministry of Science and Technology and by the Nano System Institute – National Core Research Center (NSI) through KOSEF, Korea