Metallic temperature dependence of resistivity in perchlorate doped polyacetylene

TL;DR

This study investigates how the electrical resistivity and thermoelectric power of perchlorate-doped polyacetylene vary with temperature, revealing metallic behavior at high conductivity and a crossover at lower conductivities, with the doping method being crucial.

Contribution

It demonstrates that using anhydrous Fe(ClO_4)_3 as a dopant yields positive temperature coefficient of resistivity in polyacetylene across a wide temperature range, highlighting the importance of doping material.

Findings

Highly conducting samples show positive TCR from 1.5K to 300K.

Less conducting samples exhibit a crossover with a broad minimum at T* > 200K.

Resistivity at 1.5K can be lower than at room temperature in highly conducting samples.

Abstract

We have measured the electrical resistivity ($\rho$) and the thermoelectric power (TEP) of the perchlorate (ClO4^-) doped stretch oriented polyacetylene (PA) film. For the highly conducting samples ($\sigma_{RT} > 41000 S/cm$), the temperature dependence of the 4-probe resistivity shows positive temperature coefficient of resistivity (TCR) from T=1.5K to 300K. For the less conducting samples, the 4-probe resistivity data show the crossover of TCR with a broad minimum peak at T=T* > 200K. For samples of $\sigma_{RT}$$>$20000 S/cm, the $\rho (1.5K)/\rho (300K) <1$, i.e., the resistivity at 1.5K is lower than the room temperature resistivity value. The temperature dependence of the TEP shows diffusive linear metallic TEP becoming temperature independent below 40K. Unlike the others who used Cu(ClO_4)_2 for the ClO_4^- doping, the initial doping material we used is anhydrous Fe(ClO_4)_3 which is crucial to obtain the positive TCR from T=1.5K to 300K.