Electronic mobility in rutile (TiO2) at high temperatures

Physica Status Solidi (b)

Бак

Burg

2007

IN MEMORIAM. This paper is dedicated to the memory of Dr. J. Bruce Wagner, Jr. (1926–2006), long time Professor of Materials Science and Engineering at the Northwestern University, Evanston, IL and Regents Professor of the Arizona State University, Tempe, AZ. Professor Wagner was prominent scientist in the area of solid‐state science, electrochemistry and high temperature chemistry. He served as Director of the Material Research Centre at the Technological Institute of Northwestern University, Director of the Centre for Solid State Science at the Arizona State University. He was also the President of the Electrochemical Society.The present work reports the electrical properties for high purity polycrystalline TiO2 using the measurements of electrical conductivity in the temperature range 1123–1323 K and in the gas phase of controlled oxygen activity (10–13 Pa < p (O2) < 105 Pa). The slope of the log σ vs. log p (O2) dependence is –1/5.4, which is considered in terms of mixed electronic and ionic compensation. The electrical conductivity data within the n –p transition were used for the determination of the conductivity components related to electrons, electron holes and ions. These data were used for the determination of the n –p transition point. The band gap determined from the conductivity components related to electronic charge carriers is equal to 2.8 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Section: Brief Reference Overviewmentioning

confidence: 94%

Electrical properties of polycrystalline TiO₂ at elevated temperatures. Electrical conductivity

Physica Status Solidi (b)

Бак

Burg

2007

“…As seen, the electrical conductivity data of Blumental et al 10 Baumard et al 14-18 exhibit the p(O 2 ) exponent about 21/5 within the entire studied p(O 2 ) range. While the slope 1/m s 521/6 may be considered in terms of the strongly reduced regime, the slope 1/m s 521/5 seems to be related to the transition regime between the strongly reduced regime and the reduced regime owing to the following reasons: (i) Ti interstitials are the predominant defects only in extremely reduced conditions 1,2 (ii) in the conditions of p(O 2 ) and temperature reported by Blumenthal et al [10][11][12] and Baumard et al [14][15][16][17][18] , the concentration of oxygen vacancies is still substantial. 1 The data of Balachandran and Eror 28 exhibit a change of the slope at p(O 2 )5about 10 210 -10 26 Pa, however, their p(O 2 ) exponent values are different from those of Blumental et al [10][11][12] The recent examination of the electrical conductivity by Nowotny et al, 32 which are shown in Fig.…”

Section: Overview Of Experimental Datamentioning

confidence: 96%

Electrical conductivity of TiO₂within n–p transition Part I – Verification of defect disorder model

Бак

Advances in Applied Ceramics

2007

The present paper reports semiconducting properties and the related defect disorder for undoped TiO 2 single crystal using measurements of the electrical conductivity. Isothermal changes of the electrical conductivity as a function of oxygen activity were determined within oxygen activities ranging between 10 Pa and 75 kPa and temperatures between 1073 and 1323 K. The electrical conductivity data, involving both n and p type regimes, are considered in terms of defect disorder assuming that the predominant mobile defects are oxygen vacancies, which are compensated by immobile titanium vacancies. Application of this model led to the determination of the electrical conductivity components related to electrons, electron holes and ions. The determined empirical relationships between electrical conductivity and oxygen activity may be used for predicting the effect of experimental conditions on semiconducting properties of TiO 2 . The activation energy for the standard conductivity component of electrons and holes is 226 and 102 kJ mol 21 respectively.

“…1 The electrical conductivity data at 1273 K as a function of oxygen activity reported in the literature. [3][4][5][6][7][8][9][10][11] Since electrical properties are very sensitive to defect disorder, the measurements of these properties, such as electrical conductivity, may be used for assessment of the defect disorder. The latter one may be represented in the form of a diagram showing the concentration of defects, including both ionic and electronic defects, as a function of oxygen activity, p(O 2 ), in equilibrium.…”

Section: Definition Of Termsmentioning

confidence: 99%

Defect Chemistry and Electrical Properties of Titanium Dioxide. 2. Effect of Aliovalent Ions

et al. 2007

The present work considers the effect of aliovalent ions (donors and acceptors) on the concentration of electronic charge carriers (electrons and electron holes) in titanium dioxide at elevated temperatures (873-1373 K) and the related electrical properties. The data are derived in the form of diagrams representing (i) the concentration of electronic charge carriers and (ii) electrical conductivity as a function of the effective concentration of acceptors. These diagrams may be used to predict the effect of acceptors and donors on the electrical conductivity for both n-and p-type TiO 2 . It is shown that the concentration of aliovalent ions, added intentionally (dopants) or unintentionally (impurities), has a substantial effect on the semiconducting properties already at the level of several parts per million and, therefore, cannot be ignored. This effect increases with the increasing oxygen activity. The determined critical concentrations of acceptors at 1073 K decreases from 10 -3 at p(O 2 ) ) 10 -10 Pa to 10 -6 at p(O 2 ) ) 75 kPa. These data indicate that well-defined TiO 2 specimens must include an analysis of impurities showing the concentration of aliovalent ions at the level of several parts per million.