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Due to unique optical/mechanical properties and significant resistance to harsh radiation environments, corundum (α-Al2O3) is considered as a promising candidate material for windows and diagnostics in forthcoming fusion reactors. However, its properties are affected by radiation-induced (predominantly, by fast neutrons) structural defects. In this paper, we analyze thermal stability and recombination kinetics of primary Frenkel defects in anion sublattice − the F-type electronic centers and complementary oxygen interstitials in fast-neutron-irradiated corundum single crystals. Combining precisely measured thermal annealing kinetics for four types of primary radiation defects (neutral and charged Frenkel pairs) and the advanced model of chemical reactions, we have demonstrated for the first time a co-existence of the two types of interstitial defects – neutral O atoms and negatively charged O- ions (with attributed optical absorption bands peaked at energies of 6.5 eV and 5.6 eV, respectively). From detailed analysis of interrelated kinetics of four oxygen-related defects, we extracted their diffusion parameters (interstitials serve as mobile recombination partners) required for the future prediction of secondary defect-induced reactions and, eventually, material radiation tolerance. [ABSTRACT FROM AUTHOR]

The effect of ultrasonic treatment (UST) on the defect structure of the Si-SiO2 system by means of electron spin resonance (ESR), metallography, MOS capacitance technique and secondary ions mass-spectroscopy (SIMS) is presented. The non-monotonous dependence of the defect densities on the US wave intensity has been observed. The influence of the UST frequency on the ESR signal intensity of the defect centres depended on the defects type and structure and may becaused by vibrational energy dissipation which are a functions of defect's centers type. The influence of the UST on the Si-SiO2 interface properties depends on the oxide thickness and crystallographic orientation. The density of point defects and absorbed impurities at the Si-SiO2 interface can be reduced and its electrical parameters improved by an appropriate choice of the UST and oxidation conditions. [ABSTRACT FROM AUTHOR]

High temperature electrical conductivity (HTEC) as a function of time after step-like change of Zn vapor pressure ( PZn) at fixed ZnO crystal temperature ( TZnO) and after step-like change of TZnO at fixed PZn was measured in undoped ZnO single crystal and in undoped ZnO ceramic sample. It was found a difference on HTEC relaxation curves in these measurements. Samples were cooled from temperature 1273 K to room temperature. Appearance of asymmetric spectrum with g≈1.96 and disappearance of Mn2+ spectrum were detected in EPR investigations. Then vacuum annealing was applied for these samples and intensity of g≈1.96 EPR spectrum was registered after every vacuum annealing cycles. The change in sample color, the change in g≈1.96 spectrum intensity as well as appearance again of Mn2+ EPR spectrum in the course of vacuum annealing was explained by the model of defect clusters formed during cooling of the crystal. (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

We have studied the effect of CaF2:Eu luminophore synthesis methods on the charge state of europium. We have shown that Eu3+ predominates over Eu2+ in samples obtained by coprecipitation of europium with calcium fluoride, and the ratio Eu3+/Eu2+ grows as the total amount of europium increases. Partial charge conversion of the europium occurs during calcination of the samples, due to changes in the excess fluorine balance. We studied the luminescence, magnetic susceptibility, and EPR of the synthesized samples. We have shown that in a solid solution, europium forms large ordered clusters, determining both the luminescent and the magnetic properties of the material. [ABSTRACT FROM AUTHOR]

A single radiation-induced superoxide ion O 2 - has been observed for the first time in metal oxides. This structural defect has been revealed in fast-neutron-irradiated (6.9×1018n/cm2) corundum (α-Al2O3) single crystals using the EPR method. Based on the angular dependence of the EPR lines at the magnetic field rotation in different planes and the determined g tensor components, it is shown that this hole-type O 2 - center (i) incorporates one regular and one interstitial oxygen atoms being stabilized by a trapped hole (S = 1/2), (ii) occupies one oxygen site in the (0001) plane being oriented along the a axis, and (iii) does not contain any other imperfection/defect in its immediate vicinity. The thermal stepwise annealing (observed via the EPR signal and corresponding optical absorption bands) of the O 2 - centers, caused by their destruction with release of a mobile ion (tentatively the oxygen ion with the formal charge −1), occurs at 500–750 K, simultaneously with the partial decay of single F-type centers (mostly with the EPR-active F+ centers). The obtained experimental results are in line with the superoxide defect configurations obtained via density functional theory (DFT) calculations employing the hybrid B3PW exchange-correlation functional. In particular, the DFT calculations confirm the O 2 - center spin S = 1/2, its orientation along the a axis. The O 2 - center is characterized by a short O–O bond length of 1.34 Å and different atomic charges and magnetic moments of the two oxygens. We emphasize the important role of atomic charges and magnetic moments analysis in order to identify the ground state configuration. [ABSTRACT FROM AUTHOR]