Universal dielectric response in granular media.

Stress-dependent electrical transport and its universal scaling in granular materials

https://doi.org/10.1016/j.eml.2018.05.005

Recent research has investigated electrical transport in granular systems. A phenomenon that is very important in diverse energy materials. By considering mulitple physical effects, the origins of a power law scaling are revealed with profound implications for energy systems including batteries, fuel cells and more. An in depth discussion explores how contact mechanics, granular packings and equivalent resistor and capacitor elements combine to yield the overall system response in heterogeneous systems. 

Full text and arXiv documents

Abstract

We experimentally and numerically examine stress-dependent electrical transport in granular materials to elucidate the origins of their universal electrical response. The dielectric responses of granular systems under varied compressive loadings consistently exhibit a transition from a resistive plateau at low frequencies to a state of nearly constant loss at high frequencies. By using characteristic frequencies corresponding to the onset of conductance dispersion and measured direct-current resistance as scaling parameters to normalize the measured impedance, results of the spectra under different stress states collapse onto a single master curve, revealing well-defined stress-independent universality. In order to model this electrical transport, a contact network is constructed on the basis of prescribed packing structures, which is then used to establish a resistor–capacitor network by considering interactions between individual particles. In this model the frequency-dependent network response meaningfully reproduces the experimentally observed master curve exhibited by granular materials under various normal stress levels indicating this universal scaling behaviour is found to be governed by (i) interfacial properties between grains and (ii) the network configuration. The findings suggest the necessity of considering contact morphologies and packing structures in modelling electrical responses using network-based approaches.