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

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• 作者：Yoshitaka Aoki ; Hiroki Habazaki ; Shinji Nagata ; Aiko Nakao ; Toyoki Kunitake ; Shu Yamaguchi
• 刊名：Journal of the American Chemical Society
• 出版年：2011
• 出版时间：March 16, 2011
• 年：2011
• 卷：133
• 期：10
• 页码：3471-3479
• 全文大小：1110K
• 年卷期：v.133,no.10(March 16, 2011)
• ISSN：1520-5126

文摘

The finite size effect of proton conductivity of amorphous silicate thin films, a-M_0.1Si_0.9O_x (M = Al, Ga, Hf, Ti, Ta, and La), was investigated. The proton conductivity across films, 蟽, was measured in dry air by changing the thickness in the range of 10鈭?000 nm. 蟽 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鈥檚 of nanometers. On the other hand, 蟽 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 R₁ and R₂ (R₁ > R₂) in the form of a simple cubic-type lattice. High-resolution TEM clarified that a-M_0.1Si_0.9O_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鈥檚 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.