Percolation exponents and thresholds obtained from the nearly ideal continuum percolation system graphite-boron nitride
- Department of Physics and Condensed Matter Physics Research Unit, University of the Witwatersrand, P.O. WITS 2050, Johannesburg (South Africa)
Compressed disks made from graphite and, its mechanical but not electrical isomorph, boron nitride as well as graphite-boron nitride powders, undergoing compression, are nearly ideal continuum percolation systems, as the ratio of their conductivities is nearly 10{sup {minus}18} and the scatter of the experimental points near the critical volume fraction {phi}{sub c} is very small. The following measurements, with the characteristic exponent(s) in brackets, are made on some or all of the samples in (axial) and at right angles (radial) to the direction of compression, as a function of the volume fraction of graphite ({phi}); dc conductivity (s and t), dielectric constant (s), magnetoresistivity (t{sub {perpendicular}}), and noise power (K). The noise power is also measured as function of resistance (w) and volume (b{sup {prime}}). The {phi}{sub c}{close_quote}s obtained for all measurements are consistent and explicable. The results for the exponents are less well understood but, where possible, these results are compared with theoretical predictions and previous experiments. The reasons for the nonuniversality of t are clarified. {copyright} {ital 1997} {ital The American Physical Society}
- OSTI ID:
- 526992
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 56, Issue 3; Other Information: PBD: Jul 1997
- Country of Publication:
- United States
- Language:
- English
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