BaTiO sub(3- delta ): Defect Structure, Electrical Conductivity, Chemical Diffusivity, Thermoelectric Power, and Oxygen Nonstoichiometry

• Published in: Journal of electroceramics 2002-07, Vol.8 (1), p.5-36
• Main Authors: Yoo, Han-Ill, Song, Chang-Rock, Lee, Doh-Kwon
• Format: Article
• Language: English
• Subjects: Defects; Diffusivity; Electric power generation; Electrical conductivity; Electrical resistivity; Electronics; Resistivity; Thermoelectricity
• ISSN: 1385-3449; 1573-8663
• DOI: 10.1023/A:1015570717935

Electrical conductivity, thermoelectric power, and chemical diffusivity are the most typical, charge-and-mass transport properties of a mixed ionic electronic conductor oxide which are essentially governed by its defect structure, and the oxygen nonstoichiometry is a direct measure of its overall defect concentration. For the system of BaTiO sub(3- delta ), the total electrical conductivity has been the most extensively and systematically studied as a function of oxygen partial pressure at elevated temperatures. The other properties have also been studied, but much less extensively and systematically. The electrical conductivity and thermopower were occasionally measured together on the same specimens so that mutual compatibility or consistency might be secured. But, the rest were all determined separately on the specimens of differing quality, consequently lacking in mutual consistency. It, thus, has remained hard to evaluate the canonical, defect-chemical parameters which are consistent with each and every of these defect structure-sensitive properties that were observed. Very recently the authors have determined the total conductivity, chemical diffusivity and thermoelectric power altogether on the same specimens of BaTiO sub(3- delta ), and the nonstoichiometry on the same-quality specimens at temperatures of 1073 less than or equal to T/K less than or equal to 1373 over wide enough a range of oxygen partial pressure (normally, 10 super(-16) less than or equal to Po sub(2)/atm less than or equal to 1) that encloses an electron/hole/ion mixed regime. In this article, we will compile all the literature data on these defect-structure-sensitive properties and extract from the authors' own, without using any ad hoc assumptions regarding, e.g., the electronic carrier mobilities and effective density of states, the basic defect-chemical parameters including defect-equilibrium constants, carrier mobilities and densities, and electronic heats of transport, which are the most consistent with the properties observed. Compared to the conventional picture of the defect structure of "undoped" BaTiO sub(3), thus, some new insights into the defect chemical nature of BaTiO sub(3- delta ) are provided.