Microwave Conductivity and Raman Spectroscopy of Porous TiO2

✍ Scribed by Porteanu, H.E. ;Timoshenko, V.Yu. ;Dittrich, Th. ;Koch, F.

• Publisher: John Wiley and Sons
• Year: 2000
• Tongue: English
• Weight: 111 KB
• Volume: 182
• Category: Article
• ISSN: 0031-8965
• DOI: 10.1002/1521-396x(200011)182:1<201::aid-pssa201>3.0.co;2-r

✦ Synopsis

Microwave conductivity and Raman spectroscopy were applied to study the influence of light and thermal annealing on porous TiO 2 properties. Microwave absorption in porous TiO 2 (anatase) showed an anomalous behaviour in the presence of light excitation (at 514 nm, i.e. below, or 356 nm, i.e. above the band gap). Exposure to light at a time scale of minutes reduces the microwave conductivity, in contrast to many bulk semiconductors excited above band gap. A reduced content of oxygen after heating in vacuum leads also to a reduction of microwave absorption. Both observations are in apparent contradiction with dc conductivity in TiO 2 . By comparison with lightinduced EPR experiments, we conclude that the oxygen removal creates deep defects to which are transferred electrons previously trapped in shallow donors. As a consequence, this decreases the polarisability of TiO 2 nanoparticles, the microwave absorption, and the dielectric constant.