Scaling of ac electrical conductivity of powders under compression

Abstract

We measured, at low applied voltage, the ac electrical resistance and capacitance of a metallic powder sample under uniaxial compression. Whatever the applied stress, the frequency-dependent resistance curves can be displayed on a master curve by an appropriate rescaling. The same property is also observed for the capacitance. A one-dimensional model shows that the strong frequency dependence of the macroscopic resistance and capacitance is a consequence of the broad contact resistance distribution between grains. No microscopic model of conduction nor any parameter related to the unknown disorder need to be assumed. Relevance to other systems like random conductor-insulator mixtures or metal-cluster compounds is discussed.

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

“…In order to further study the effects of component values on the resultant electrical responses, we conducted simulations with resistors and capacitors of various magnitudes, detailed in Supplementary Materials. The observed insensitivity of network responses to the properties and positions of elements is consistent with previous literature [8,17,22,24] .…”

“…However, the observed close power exponent values for dependence of * on * ̅̅̅ and * on * ̅̅̅ demonstrate that the characteristic frequency is mainly governed by * for the considered experimental conditions in this work. Noted that the value of * can be also affected by the surface structure of contacting spheres [34,38,41], material properties [19,22,36], grain size [8,10] and applied load [52]. For 10 mm spheres, absolute exponent values of 0.83 ± 0.14 and 0.32 ± 0.09 can be found, corresponding to the five lowest and highest load levels, respectively.…”

The effect of organic additives on the intergranular conductivity of Al-doped ZnO

“…The deviation from Hertz law for the graed powders indicates the non-uniformity of the surface layer as well as the contribution of plastic deformations. 43 All the resistivity measurements show an excellent reproducibility above 2 Â 10 6 Pa. All the molecules used in this study present a positive effect on the conductivity, except for the nonconjugated succinic acid, SA, which does not show any effect at all (the resistivity versus applied pressure exactly superposes with the ungraed material in Fig. 6) Thus, a conjugated pisystem is necessary to improve the intergranular conductivity.…”

“…For an ideal powder of spherical particles with no surface layer, the Hertz model, describing the surface contact area between particles as a function of the applied pressure, predicts that in the elastic regime g ¼ À2/3. 42,43 The values of g obtained on our experimental curves is 1.2 for ungraed ZnO:Al. The deviation from Hertz law for the graed powders indicates the non-uniformity of the surface layer as well as the contribution of plastic deformations.…”

Some aspects of electrical conduction in granular systems of various dimensions

“…The situation for 3D Copper powder samples will be clarified in [31]. Let us add a few comments about the interplay between the irreversibility threshold occuring at a constant dissipated power (P c ), and the saturation threshold (U = 0.4V per contact).…”