Dresden 2009 – wissenschaftliches Programm
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MM: Fachverband Metall- und Materialphysik
MM 32: Topical Session High Temperature Materials III
MM 32.4: Vortrag
Mittwoch, 25. März 2009, 17:45–18:00, IFW A
Oxygen vacancies in yttria-stabilized zirconia: defect configurations and charge states — •Volker Haigis, Felix Hanke, and Matthias Scheffler — Fritz-Haber-Institut, Berlin
Yttria-stabilized zirconia (YSZ) is a standard material for thermal barrier systems, where it is used to shield critical parts of combustion engines from high temperature environments. This application of YSZ is due to its low thermal conductivity and its phase stability over a wide temperature range [1]. Doping of zirconia (ZrO2) with yttria (Y2O3) introduces oxygen vacancies which play a crucial role in stabilizing the technologically relevant tetragonal structure. In spite of some work on structural properties [2], the current understanding of the material at the atomic scale is sparse. Here, we characterize the oxygen vacancies, including their charge states, defect configurations, and concentration in YSZ in an oxygen atmosphere. Relevant defect arrangements are identified, and the respective Gibbs free energies are calculated using ab initio atomistic thermodynamics. In addition to standard density functional theory, the GGA+U method is used to analyse the stability of vacancy charge states. We construct a phase diagram giving the thermodynamically stable configurations as a function of the Fermi level, temperature, and oxygen pressure. It is discussed whether non-stoichiometric compositions (more or less than one vacancy per two yttrium atoms) are to be expected at finite temperatures and pressures, and hence under technologically relevant conditions.
[1] A.G. Evans et al., J. Eur. Ceram. Soc. 28, 1405 (2008)
[2] A. Eichler, Phys. Rev. B 64, 174103 (2001)