Papers by Author: V.I. Tsidilkovski

Abstract: Defect formation in yttria with a small content of acceptor impurities in equilibrium with a hydrogen-containing gas phase is studied theoretically. A statistical-thermodynamic description of the yttriagas equilibrium is based on the approach developed for compounds with a complex electronic structure [Phys. Stat. Sol. B (1991) Vol. 168, p. 233]. The considered model of electronic structure for Y₂O₃ includes, besides valence and conduction bands, acceptor and F-center states. The energy of F-centers was calculated in the framework of the variational quantum-mechanical approach combined with the molecular statics method. It is shown that acceptor states appreciably affect the thermodynamics of defect formation, while the F-centers contribution in a wide range of external parameters is small. The concentrations of defects (protons, oxygen vacancies, electronic defects) and the Fermi level position are determined as functions of temperature and gas phase parameters.

Abstract: The tracer diffusion coefficient D* and the mobility of protons in proton-conducting oxides of the АIIВIV 1-xRIII xO3-δ family have been calculated using the Monte Carlo method as functions of temperature and concentration x of the acceptor impurity RIII. The effect of protondopant interactions (proton trapping) and the effect of protonic sites blocking caused by protonproton and proton - oxygen vacancy interactions, are analyzed. It is shown that the proton diffusivity depends significantly on the dopant content and is considerably reduced already at small x. The D* value weakly depends on the concentration of oxygen vacancies at fixed, not too large values of x. The conductivity dependence on the doping concentration σ(x) can have a maximum due to the proton-defect and proton-proton interactions. The Haven ratio deviates slightly from unity at the expected intensity of interparticle correlations. The calculated values of both the diffusivity activation energy increase (with x), and the location of the σ(x) maxima agree with the experimental data for a number of proton-conducting oxides.