A model for inhomogeneous conduction in anisotropic materials: application to (SN)x

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Abstract
A resistor-network model has been devised which sheds light on many of the resistive properties of inhomogeneous, anisotropic conductors. The model is applied to explain the changes of resistance with temperature (1.5-300K) and pressure (0-140 bar) for samples of (SN)x subjected to small amounts of mechanical damage. The well-known minimum of resistance with respect to temperature frequently seen in (SN)x is due to inhomogeneous current flow, which is greatly enhanced by mechanical damage, while the inhomogeneity which gives rise to the slight minimum in the starting material (apparent resistance ratio of about 40) can be allowed for, giving a corrected resistance ratio of about 120, and also giving corrected values of rho /sub /// (T) over the range 2-300K. The value of d ln rho /sub ////d ln T is approximately two above about 100K, but falls to almost unity near 40K before rising to values of about four below 10K in a way characteristic of phonon scattering with theta R approximately=43K. The quasi-T2 form of rho /sub ///(T) at high temperatures results from thermal expansion, and no evidence is found for any intrinsic 'T2' behaviour.