Correlations among defect type, photoconductivity and photoreactivity of doped TiO 2
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Correlations Among Defect Type, Photoconductivity and Photoreactivity of Doped TiO2 Myong-Ho Kim +, Soon-ll Lee, Tae-Kwon Song, Hyunwoong Park*, Wonyong Choi*, Han-llt Yoo** and Tae-Gone Park *** Department of Ceramics Engineering, ***School of Mechatronics, Changwon National University, 9 Sarim-Dong, Changwon, Gyungnam 64f-773, Korea *School of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 790-784, Korea **School of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea (Received 30 Aug~tst 2001 9 accepted 15 October 2001)
Abstract-The electrical conductivity t ~5), photoconductivity and photocatalytic reactivity in doped custalline TiO, were measured as a function of the oxy,gen partial pressure IPQ,). temperature, doping type and t IV irradiation. The Poe dependence of ~5 suggests that the predominant atomic defects in pure TiO, are oxygen vacancies (V;} and interstitial titanium kms t-ti, ), but the dominant deliect is changed with Po, and temperature, The photoexcited electrons in reduced and/or n-~,pe doped TiO: enhance both the phomconductivity and the photocatalytic reactivity by the reduction process. Tberei%re, these behaviors are strongly dependent on the electron concentration. Key words: Defect Type, Photoconductivity, Photoreactivity, Charge Compensation, Doping EffEct
INTRODUCTION
electroded with PI paste and heat treated at l~000"C for 15 rain.
2. Electrical Conductivity After the sample was printed by Pt paste (Hemeus Co,) and annealed for 15 min at 1,000'~C, the sample for the electrical conductivity was attached to PI wires (00.2 ram) for the four point-probe method to eliminate nonohmic contact eflizcts. Fig. 1 shows the apparatus for measuring electrical conductivity. The low oxygen partial pressure (P~) was established by using CO/CQ or Hfl-t:O/Ar mixture as shown in Fig. 1. "fhe established P~ was monitored with a Y_,O~stabilized zireonia (YSZ) oxygen sensor. The resistivity of the sample was measured as a function oftenperamre (700"C-1,300"C) and partial pressure of oxygen (10 *-10 2~atrn). That was converted into electrical conductivity by the following equation
Nonstoichiometric titanium dioxide, which is classified as an oxygen-deficient n-type s,vniconducto~; is one of the most extensively studied metal oxides, because it is one of the promising materials as a Note, catalyst [Fujishima, and l londa, 1972: Kasuge et al., 1997; Jongh et aI., 1997: Nakato et al., 1997; Chaiet al., 2000], oxygen sensor [lien et al., 1975; Baeket al., 1999], varistor, and oxide electrode [Zaban et aL 1997: Watanabe et al., 19761, The photocatalytic mechanism is still controversial, although there are many articles reporting the correlation of photocatalytic activity with the physical preD.:ties of TiO: such as crystal structure, surface area, particle size, and so on [Ohtan[ et at., I997]. The purpose of this research is to investigate the correlation between the photoconductivity and the photocatalytic reactivity in undoped and dop
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