Percolative proton conductivity of sol–gel derived amorphous aluminosilicate thin films

Abstract

The finite size effect of proton conductivity of amorphous aluminosilicate thin films, a-Al(n)Si(1-n)O(x) (n = 0.07, 0.1, 0.2, 0.3 and 0.45), prepared by a sol-gel process was investigated by experimental and numerical techniques. High-resolution TEM clarified that a-Al(n)Si(1-n)O(x) films had the heterogeneous nanoscale microstructures comprised of the ion-conducting, condensed glass microdomain and the poor-conductive, uncondensed glass microdomain. σ of the films with n≤0.1 exponentially increased upon decreasing thickness in the sub-100 nm range because the volume fraction of conductive domains was less than the percolation threshold and cluster size scaling of the conductive domain was operative. The numerical simulation suggested that conductance of the condensed domain was higher than that of the uncondensed domain by 2 orders of magnitude. Volume fractions of the condensed domain increased with increasing Al/Si molar ratio and were over the percolation threshold (24.5%) with n≥0.2. However, conductance of the condensed domain decreased with increasing Al/Si ratio with n≥0.2 because the aluminosilicate glass framework made of 4-fold-connected MO(4) tetrahedra was deformed by forming the octahedral AlO(6) moieties, as checked by Al K-edge XAS. It was found that the optimal Al/Si composition in terms of the conductance of the condensed domain is not in coincidence with that in terms of the average conductivity of the films.

Review: recent progress in low-temperature proton-conducting ceramics

“…Aoki et al [127] reported the proton conductivity of amorphous Al n Si 1-n O x thin film which has the heterogeneous nanoscale microstructure comprised of the ion-conducting, condensed glass microdomain and a poorly conductive, uncondensed glass microdomain.…”

A Review on Low-Temperature Protonic Conductors: Principles and Chemical Sensing Applications

“…Some tin derivates have also been reported to display excellent ionic conduction properties [94]. Clays like silicon dioxide (silica) and aluminosilicate porous structures exhibit similar behavior, particularly those prepared by the sol-gel method [95,96]. Between silica crystalline and amorphous phases, the latter is highly chosen to produce inorganic membranes due to the possibility of forming structures with mesopores and micropores, whose size distribution can be tuned, for instance, using the parameters of the sol-gel process [97].…”

Compositional Dependence of the Proton Conductivity of Anodic ZrO2-WO3-SiO2Nanofilms at Intermediate Temperatures

“…In several glassy ion conducting thin films similar exponential increase of the ion conductivity across the nanometer-thick films with a reduction of film thickness have been found. 17,[28][29][30] When the thickness of the glass film is close to the length of the largest highly ion-conducting pathway inside a film, the pathway percolating from one to another electrode/electrolyte interface is involved in the ion conduction, and thus the overall conductivity across the film must be increased with reducing the film thickness. In the finite-size percolation model, highly conducting channels are present in the poorly conducting matrix.…”