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Charge trapping in TiO2 polymorphs as seen by Electron Paramagnetic Resonance spectroscopy
Mario Chiesa1, Maria Cristina Paganini, Stefano Livraghi
1Dipartimento di Chimica and NIS, Università di Torino, Torino, Italy.
Physical Chemistry Chemical Physics : PCCP
|May 23, 2013
Summary
Electron Paramagnetic Resonance (EPR) reveals distinct electron trapping behaviors in TiO2 polymorphs. Anatase shows delocalized electron density, while rutile exhibits localized density in interstitial sites.
Area of Science:
- Materials Science
- Solid State Physics
- Spectroscopy
Background:
- Titanium dioxide (TiO2) is a crucial material with distinct polymorphs, anatase and rutile.
- Understanding charge carrier trapping in TiO2 is vital for its applications.
- Electron Paramagnetic Resonance (EPR) is a powerful technique for probing paramagnetic species.
Purpose of the Study:
- To investigate and differentiate electron trapping sites in anatase and rutile TiO2.
- To clarify the nature and localization of electron spin density in these polymorphs.
- To provide guidelines for interpreting EPR signals in TiO2.
Main Methods:
- Continuous Wave (CW-EPR) spectroscopy to analyze g tensor signals.
- Pulse-EPR hyperfine techniques utilizing oxygen-17 (17O) enrichment.
- Systematic analysis of signals from bulk and surface, regular and defective sites.
Main Results:
- CW-EPR provided systematic guidelines for interpreting signals in both anatase and rutile.
- Pulse-EPR with 17O enrichment revealed differences in electron spin density localization.
- Anatase exhibits delocalized electron density at regular lattice sites.
- Rutile shows localized electron density at interstitial sites.
Conclusions:
- Significant differences in electron wavefunction localization exist between anatase and rutile TiO2.
- EPR techniques, particularly pulse-EPR, are effective in distinguishing these trapping mechanisms.
- This research clarifies electron trapping in TiO2, aiding material design and application.
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