Electrical properties of polycrystalline TiO₂ at elevated temperatures. Electrical conductivity

Abstract

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)

Electrical properties of polycrystalline TiO2: Equilibration kinetics

“…The experiments were performed within several narrow ranges of p(O 2 ) to assess the changes of D chem with p(O 2 ). The experimental monitoring sheet showing the changes of oxygen activity, p(O 2 ), the temperature, T, and the electrical conductivity, σ , during reduction experiment at 1,273 K was reported before [17]. It was shown that imposition of a new p(O 2 ) results in instantaneous increase of p(O 2 ), which reaches its nominal value within 10 min.…”

“…The specimen and the experimental setup were described before [17,18]. Electrical conductivity was determined using high temperature Seebeck probe [19].…”

Effect of cooling on electrical conductivity of TiO2

“…The electrical conductivity for polycrystalline specimen of undoped TiO 2 in oxygen, p(O 2 ) = 75 kPa, in the range 1073-1323 K, were reported elsewhere [31]. The specimens in the oxidising conditions were not studied during cooling since their conductance on cooling below 1073 K becomes unmeasurable.…”

“…Isothermal changes of the electrical conductivity for high purity TiO 2 single crystal as a function of oxygen activity in the range 1073 -1323 K [31]. The data for high purity polycrystalline TiO 2 at 1273 K is also included.…”

“…The time gap was adjusted according to the rate of the conductivity change. The details of the applied experimental procedure are described elsewhere [31]. 2 The effect of cooling rate on the electrical conductivity of TiO 2 equilibrated at 1273 K and p(O 2 ) = 10 Pa (argon) during slow and fast cooling is shown in Fig.…”