Structure of and ion segregation to an alumina grain boundary: implications for growth and creep

Using periodic density-functional theory (DFT), we investigated the structure and cohesive properties of the �-alumina �11 tilt grain boundary, with and without segregated elements, as a model for the thermally grown oxide in jet engine thermal barrier coatings. We identified a new low-energy structure different from what was proposed previously based on electron microscopy and classical potential simulations. We explored the structure and energy landscape at the grain boundary for segregated Al, O, and early transition metals (TMs) Y and Hf. We predict that the TMs preferentially adsorb at the same sites as Al, while some adsites favored by O remain unblocked by TMs. All segregated atoms have a limited effect on grain boundary adhesion, suggesting that adhesion energies alone cannot be used for predictions of creep inhibition. These findings provide some new insights into how TM dopants affect alumina growth and creep kinetics. I

Quantum Dimensional Zeeman Effect in the Magneto-optical Absorption Spectrum for Quantum Dot - Impurity Center Systems

Magneto-optical properties of the quantum dot - impurity center (QD-IC) systems synthesized in a transparent dielectric matrix are considered. For the QD one-electron state description the parabolic model of the confinement potential is used. Within the framework of zero-range potential model and the effective mass approach, the light impurity absorption coefficient for the case of transversal polarization with respect to the applied magnetic field direction, with consideration of the QD size dispersion, has been analytically calculated. It is shown that for the case of transversal polarization the light impurity absorption spectrum is characterized by the quantum dimensional Zeeman effect.Comment: 18 pages, 1 figure, PDF fil