Local geometric and electronic structures of gasochromic VO(x) films.
VOx films were deposited by radio-frequency reactive magnetron sputtering from a vanadium target at room temperature. Local atomic and electronic structures of the films were then modified by thermal annealing. The oxidation state and structural and gasochromic properties of the films were elucidated by X-ray absorption spectroscopy. Analytical results indicate that the as-deposited VOx films were amorphous with mixed V(4+) and V(5+) valences. The amorphous VOx had a disordered and expanded lamellar structure resembling that of polymer-intercalated V2O5 gels. VOx films were crystallized into orthorhombic V2O5 at 300 °C, and the lamellar structure was eliminated at 400 °C. Additionally, the gasochromic reaction reduced the vanadium valence via intervalence transitions between V(5+) and V(3+). Moreover, removing the lamellar structure reduced the gasochromic rate, and the gasochromic reaction transformed the V2O5 crystalline phase irreversibly into an H1.43V2O5 phase. Based on the results of this study, amorphous VOx with a lamellar structure is recommended for use in H2 gas sensors.
National Synchrotron Radiation Research Center, Hsinchu 30076, Taiwan. dong.cl@nsrrc.org.tw.
Wei-Luen
WL
Jang
Yang-Ming
YM
Lu
Chi-Liang
CL
Chen
Ying-Rui
YR
Lu
Chung-Li
CL
Dong
Ping-Hung
PH
Hsieh
Weng-Sing
WS
Hwang
Jeng-Lung
JL
Chen
Jin-Ming
JM
Chen
Ting-Shan
TS
Chan
Jyh-Fu
JF
Lee
Wu-Ching
WC
Chou