Segregated tunneling-percolation model for transport nonuniversality

TL;DR

This paper introduces a model explaining how microstructure influences the nonuniversal electrical transport behavior in disordered materials, especially thick-film resistors, through tunneling processes in metallic grain chains.

Contribution

The paper presents a segregated tunneling-percolation model linking microstructure to transport nonuniversality, supported by Monte Carlo simulations.

Findings

Model explains both universal and nonuniversal transport behavior.

Power-law divergence in chain conductivities causes nonuniversality.

Applicable to thick-film resistor microstructures.

Abstract

We propose a theory of the origin of transport nonuniversality in disordered insulating-conducting compounds based on the interplay between microstructure and tunneling processes between metallic grains dispersed in the insulating host. We show that if the metallic phase is arranged in quasi-one dimensional chains of conducting grains, then the distribution function of the chain conductivities g has a power-law divergence for g -> 0 leading to nonuniversal values of the transport critical exponent t. We evaluate the critical exponent t by Monte Carlo calculations on a cubic lattice and show that our model can describe universal as well nonuniversal behavior of transport depending on the value of few microstructural parameters. Such segregated tunneling-percolation model can describe the microstructure of a quite vast class of materials known as thick-film resistors which display universal or nonuniversal values of t depending on the composition.