2009 Fiscal Year Final Research Report
Size effect on parcolative ion conductivity of amorphous metal oxide nanofilms
| Project/Area Number |
20760460
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| Research Category |
Grant-in-Aid for Young Scientists (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Structural/Functional materials
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| Research Institution | Hokkaido University |
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Principal Investigator |
AOKI Yoshitaka Hokkaido University, 大学院・工学研究科, 助教 (50360475)
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| Project Period (FY) |
2008 – 2009
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| Keywords | パーコレーション / プロトン伝導体 / アモルファス酸化物 / 電解質膜 / 燃料電池 |
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| Research Abstract |
Amorphous silicate nanofilms, a-M_<0.1>Si_<0.9>O_x, exhibit unique size-enhancement of the proton conductivity along thickness direction due to the presence of the zeolite-like, acid site network with the mesoscopically-sized length inside glass matrix. These films revealed the complex temperature-and humidity-dependency of proton conductivity by the existence of two kinds of protonic carriers: Bronsted acidic protons and Lewis acidic protons. The Bronsted acidic protons could be persistent in amorphous films at around 500℃, as checked by thermal desorption spectroscopy, so that the film exhibited the humidity-independent proton conductivity at temperatures above 300℃. Furthermore, the conductivity across the film σ increased in a power low by reduction of the film thickness d to less than 120 nm as σ ∝ d^<-τ>, and it was saturated when the thickness become less than 40 nm. The observed scaling index τ was 2.2 in agreement with the value of the theoretical index (2.3) of cluster size scaling in 3-dimensional percolation system. This conduction behavior is explicable by finite size-scaling of the highly-conductive pathway based on the interconnected Bronsted acid centers in the range of a few tens to hundreds nm.
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