Finite Size Effect of Proton-Conductivity of Amorphous Silicate Thin Films Based on Mesoscopic Fluctuation of Glass Network

Abstract

The finite size effect of proton conductivity of amorphous silicate thin films, a-M(0.1)Si(0.9)O(x) (M = Al, Ga, Hf, Ti, Ta, and La), was investigated. The proton conductivity across films, σ, was measured in dry air by changing the thickness in the range of 10-1000 nm. σ of the films with M = Al, Ga, and Ta was elevated in a power law by decreasing thickness into less than a few hundred nanometers, and the increment was saturated at a thickness of several 10's of nanometers. On the other hand, σ of the films with M = Hf, Ti, and La was not related to the decrease of the thickness in the range of >10 nm. Thickness-dependent conductivity of the former could be numerically simulated by a percolative resistor network model that involves the randomly distributed array of two kinds of resistors R(1) and R(2) (R(1) > R(2)) in the form of a simple cubic-type lattice. High-resolution TEM clarified that a-M(0.1)Si(0.9)O(x) films involved heterogeneous microstructures made of the condensed domain and the surrounding uncondensed matrix due to the fluctuation of glass networks on the nanometer scale. The condensed domain had a wormlike shape with an average length of several 10's of nanometers and performed the role of the proton conduction pathway penetrating through the poorly conducting matrix. It was concluded that the thickness-dependent conductivity could be identical to finite-size scaling of the percolative network of the interconnected domains in the nanometer range.

Thickness dependence of proton conductivity of anodic ZrO2–WO3–SiO2 nanofilms

“…6). This feature is very similar to the size-scaling of ionic conductivity found in the ion-conducting amorphous silicate thin films [20]. This size-scaling behavior is characteristic of amorphous nanofilms consisting of the highly-conducting pathway and poorly-conducting matrix with the concentration of the path below the percolation threshold.…”

Thermally Stable Super Ionic Conductor from Carbon Sphere Oxide

“…The conductivity of H 2 O‐humidified CSO is almost 1.30 times higher than the conductivity of the D 2 O‐humidified CSO (Figure c) sample. This observation indicates the proton oriented conductivities . Figure d shows that the proton conductivity increases gradually with temperature.…”

Reactions between water and vitreous silica during irradiation

“…H + diffusion into the subsurface is analogous to proton conduction and suggests that radiation damage may increase the proton conductivity of silica near water-silica interfaces; similar phenomenon has been observed in mesoporous silica [17][18][19][20]. This effect would provide a means to directly measure the extent of the radiolytic damage of glass surfaces by measuring changes in conductivity.…”

“…For example, abnormally high proton conduction has been observed in mesoporous silica [17][18][19][20], and evidence suggests that defects play a significant role in H + mobility in water-silica systems [21][22][23][24][25]. Given the fact that ballistic radiation creates large concentrations of defects in silica, it is not unreasonable to consider how radiation damage affects the mobility of H + at the silica surface and into the bulk glass.…”