Observation of double percolation transitions in Ag-SnO$_2$ nanogranular films

TL;DR

This study reports the observation of two distinct percolation transitions in Ag-SnO₂ nanogranular films, highlighting the role of tunneling effects in the second transition, thus supporting existing theories on conduction mechanisms.

Contribution

The paper provides experimental evidence of double percolation transitions and elucidates the tunneling origin of the second transition in nanogranular composites.

Findings

Two percolation thresholds observed in Ag-SnO₂ films.

Power-law behavior near each percolation threshold.

Second transition attributed to tunneling to second-nearest neighbors.

Abstract

Two percolation transitions are observed in Ag$_x$(SnO$_2)_{1-x}$ nanogranular films with Ag volume fraction $x$ ranging from $\sim$0.2 to $\sim$0.9. In the vicinity of each percolation threshold $x_{ci}$ ($i$$=$1, 2), the variation in $\sigma$ with $x$ obeys a power law for $x$$>$$x_{ci}$. The origin of the first percolation transition at $x_{c1}$ ($x_{c1}$$>$$x_{c2}$) is similar to that of the classical one, while the second transition is explained as originating from the tunneling to the second-nearest neighboring Ag particles. These observations provide strong experimental support for the validity of current theories concerning tunneling effect in conductor-insulator nanogranular composites.