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Title: ac and dc percolative conductivity of magnetite-cellulose acetate composites

Abstract

ac and dc conductivity results for a percolating system, which consists of a conducting powder (magnetite) combined with an 'insulating' powder (cellulose acetate), are presented. Impedance and modulus spectra are obtained in a percolation system. The temperature dependence of the resistivity of the cellulose acetate is such that at 170 deg. C, it is essentially a conductor at frequencies below 0.059{+-}0.002 Hz, and a dielectric above. The percolation parameters, from the dc conductivity measured at 25 and 170 deg. C, are determined and discussed in relation to the ac results. The experimental results scale as a function of composition, temperature, and frequency. An interesting result is the correlation observed between the scaling parameter (f{sub ce}), obtained from a scaling of the ac measurements, and the peak frequency (f{sub cp}) of the arcs, obtained from impedance spectra, above the critical volume fraction. Scaling at 170 deg. C is not as good as at 25 deg. C, probably indicating a breakdown in scaling at the higher temperature. The modulus plots show the presence of two materials: a conducting phase dominated by the cellulose acetate and the isolated conducting clusters below the critical volume fraction {phi}{sub c}, as well as the interconnected conductingmore » clusters above {phi}{sub c}. These results are confirmed by computer simulations using the two exponent phenomenological percolation equation. These results emphasize the need to analyze ac conductivity results in terms of both impedance and modulus spectra in order to get more insight into the behavior of composite materials.« less

Authors:
 [1];  [1];  [2];  [3]
  1. Materials Physics Research Institute and School of Physics, University of the Witwatersrand, Private Bag 3, Wits 2050 (South Africa)
  2. (South Africa)
  3. Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602 (South Africa)
Publication Date:
OSTI Identifier:
20976720
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. B, Condensed Matter and Materials Physics; Journal Volume: 75; Journal Issue: 9; Other Information: DOI: 10.1103/PhysRevB.75.094202; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; ACETATES; CELLULOSE; COMPOSITE MATERIALS; COMPUTERIZED SIMULATION; DIELECTRIC MATERIALS; ELECTRIC CONDUCTIVITY; IMPEDANCE; IRON COMPOUNDS; MAGNETITE; POWDERS; SCALING; SPECTRA; TEMPERATURE DEPENDENCE

Citation Formats

Chiteme, C., McLachlan, D. S., Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, and Sauti, G.. ac and dc percolative conductivity of magnetite-cellulose acetate composites. United States: N. p., 2007. Web. doi:10.1103/PHYSREVB.75.094202.
Chiteme, C., McLachlan, D. S., Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, & Sauti, G.. ac and dc percolative conductivity of magnetite-cellulose acetate composites. United States. doi:10.1103/PHYSREVB.75.094202.
Chiteme, C., McLachlan, D. S., Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602, and Sauti, G.. Thu . "ac and dc percolative conductivity of magnetite-cellulose acetate composites". United States. doi:10.1103/PHYSREVB.75.094202.
@article{osti_20976720,
title = {ac and dc percolative conductivity of magnetite-cellulose acetate composites},
author = {Chiteme, C. and McLachlan, D. S. and Department of Chemistry and Polymer Science, University of Stellenbosch, Private Bag X1, Matieland 7602 and Sauti, G.},
abstractNote = {ac and dc conductivity results for a percolating system, which consists of a conducting powder (magnetite) combined with an 'insulating' powder (cellulose acetate), are presented. Impedance and modulus spectra are obtained in a percolation system. The temperature dependence of the resistivity of the cellulose acetate is such that at 170 deg. C, it is essentially a conductor at frequencies below 0.059{+-}0.002 Hz, and a dielectric above. The percolation parameters, from the dc conductivity measured at 25 and 170 deg. C, are determined and discussed in relation to the ac results. The experimental results scale as a function of composition, temperature, and frequency. An interesting result is the correlation observed between the scaling parameter (f{sub ce}), obtained from a scaling of the ac measurements, and the peak frequency (f{sub cp}) of the arcs, obtained from impedance spectra, above the critical volume fraction. Scaling at 170 deg. C is not as good as at 25 deg. C, probably indicating a breakdown in scaling at the higher temperature. The modulus plots show the presence of two materials: a conducting phase dominated by the cellulose acetate and the isolated conducting clusters below the critical volume fraction {phi}{sub c}, as well as the interconnected conducting clusters above {phi}{sub c}. These results are confirmed by computer simulations using the two exponent phenomenological percolation equation. These results emphasize the need to analyze ac conductivity results in terms of both impedance and modulus spectra in order to get more insight into the behavior of composite materials.},
doi = {10.1103/PHYSREVB.75.094202},
journal = {Physical Review. B, Condensed Matter and Materials Physics},
number = 9,
volume = 75,
place = {United States},
year = {Thu Mar 01 00:00:00 EST 2007},
month = {Thu Mar 01 00:00:00 EST 2007}
}