Evidence for the formation of two types of oxygen interstitials in neutron-irradiated α-Al2O3 single crystals

AbstractDue 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.

Download Full-text

Atomic, electronic and magnetic structure of an oxygen interstitial in neutron-irradiated Al2O3 single crystals

Scientific Reports ◽

10.1038/s41598-020-72958-9 ◽

2020 ◽

Vol 10 (1) ◽

Cited By ~ 1

Author(s):

V. Seeman ◽

A. Lushchik ◽

E. Shablonin ◽

G. Prieditis ◽

D. Gryaznov ◽

...

Keyword(s):

Dft Calculations ◽

Single Crystals ◽

Density Functional ◽

Magnetic Moments ◽

Atomic Charges ◽

Interstitial Oxygen ◽

Absorption Bands ◽

Magnetic Field Rotation ◽

Formal Charge ◽

Radiation Induced

Abstract A single radiation-induced superoxide ion $$O_{2}^{ - }$$ 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 $$O_{2}^{ - }$$ 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 $$O_{2}^{ - }$$ 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 $$O_{2}^{ - }$$ O 2 - center spin S = 1/2, its orientation along the a axis. The $$O_{2}^{ - }$$ 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.

Download Full-text

On the Assignments of the Optical Absorption Bands of Radiation-Induced Radicals in Naphthalene and Anthracene Single Crystals

Molecular Crystals and Liquid Crystals ◽

10.1080/00268947908083979 ◽

1979 ◽

Vol 53 (1-2) ◽

pp. 1-13 ◽

Cited By ~ 2

Author(s):

Tetsuya Kawakubo

Keyword(s):

Optical Absorption ◽

Single Crystals ◽

Absorption Bands ◽

Radiation Induced

Download Full-text

Interactions of Self-Interstitials with Interstitial Carbon-Interstitial Oxygen Center in Irradiated Silicon: An Infrared Absorption Study

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.205-206.218 ◽

2013 ◽

Vol 205-206 ◽

pp. 218-223 ◽

Cited By ~ 4

Author(s):

Leonid I. Murin ◽

Bengt Gunnar Svensson ◽

Vladimir P. Markevich ◽

Anthony R. Peaker

Keyword(s):

Annealing Temperature ◽

Vibrational Mode ◽

Fast Neutrons ◽

Interstitial Oxygen ◽

Absorption Study ◽

Local Vibrational Mode ◽

Oxygen Center ◽

Previous Assignment ◽

Radiation Induced ◽

Kinetics Of

The evolution of radiation-induced carbon-oxygen related defects with the fluence of MeV electrons and upon subsequent isochronal annealing (75-350 °C) in Si crystals with different carbon and oxygen content has been studied by means of Local Vibrational Mode (LVM) spectroscopy. In particular, the generation kinetics of the bands at 998 and 991 cm-1 is considered and additional arguments supporting their previous assignment to the I2CiOi and I3CiOi complexes are found. An annealing behaviour of the LVMs related to the C4 (ICiOi) defect has been studied in the various Si crystals irradiated with different particles. In all the samples studied the bands at 940 and 1024 cm-1 are found to disappear at about 200 °C while three new LVM bands, at 724 cm-1 (O-related) and at 952 and 973 cm-1 (both C-related) are emerging. Further increase in annealing temperature up to 250-275 °C results in a transformation of the latter bands into another set of LVM bands at 969 cm-1 (O-related) and at 951 and 977 cm-1 (both C-related). These bands disappear upon annealing in the temperature range 300-325 °C. The ratios of all the bands intensities as well as their transformation rates do not depend on the oxygen and carbon content in the Si samples nor on the kind of irradiation (2.5 and 10 MeV electrons, fast neutrons) and irradiation doses. These facts confirm our previous conclusion that all the above-mentioned LVMs arise from the C4 defect being in different configurations (ICiOi, ICiOi*, and ICiOi**).

Download Full-text

Structural, Doped, Radiation Defects and Properties of Non-Stoichiometrical Solids

Materials Science Forum ◽

10.4028/www.scientific.net/msf.494.55 ◽

2005 ◽

Vol 494 ◽

pp. 55-60 ◽

Cited By ~ 2

Author(s):

N. Kulagin

Keyword(s):

Single Crystals ◽

Point Defects ◽

Spectral Properties ◽

Theoretical Data ◽

Radiation Defects ◽

Iron Group ◽

Radiation Induced ◽

The Stability ◽

Α Al2o3 ◽

Induced Defects

The paper includes experimental and theoretical data on spectral properties of oxide single crystals doped with ions of the iron group elements, as well as on the stability of ions oxidation state under irradiation. Experimental data resulting from the investigation of radiation-induced defects into pure and doped single crystals, such as sapphire (α-Al2O3) and garnets (Y3Al5O12, Gd3Ga2Sc3O12, Gd3Sc2Al3O12), are presented. The main conditions of creation of irradiation-induced color centers and point defects, including theoretical analysis, are considered too.

Download Full-text

Thermal decay kinetics of radiation induced optical absorption bands in LiF:Mg, Ti

Radiation Effects and Defects in Solids ◽

10.1080/10420159108224858 ◽

1991 ◽

Vol 119-121 (1) ◽

pp. 81-86 ◽

Cited By ~ 4

Author(s):

Akos Peto ◽

Andras Kelemen

Keyword(s):

Optical Absorption ◽

Thermal Decay ◽

Decay Kinetics ◽

Absorption Bands ◽

Radiation Induced ◽

Kinetics Of

Download Full-text

Study of nickel-molybdenum catalysts for methanation of carbon monoxide

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19800783 ◽

1980 ◽

Vol 45 (3) ◽

pp. 783-790 ◽

Cited By ~ 1

Author(s):

Petr Taras ◽

Milan Pospíšil

Keyword(s):

Carbon Monoxide ◽

Catalytic Activity ◽

Mixed Oxides ◽

Minor Component ◽

Fast Neutrons ◽

Scanning Calorimetry ◽

Low Concentrations ◽

Γ Rays ◽

Molybdenum Catalysts ◽

Kinetics Of

Catalytic activity of nickel-molybdenum catalysts for methanation of carbon monoxide and hydrogen was studied by means of differential scanning calorimetry. The activity of NiMoOx systems exceeds that of carrier-free nickel if x < 2, and is conditioned by the oxidation degree of molybdenum, changing in dependence on the composition in the region Mo-MoO2. The activity of the catalysts is adversely affected by irradiation by fast neutrons, dose 28.1 Gy, or by γ rays using doses in the region 0.8-52 kGy. The system is most susceptible to irradiation in the region of low concentrations of the minor component (about 1 mol.%). The dependence of changes in catalytic activity of γ-irradiated samples on the dose exhibits a maximum in the range of 2-5 kGy. The changes in catalytic activity are stimulated by the change of reactivity of the starting mixed oxides, leading to different kinetics of their reduction and modification of their adsorption properties. The irradiation of the catalysts results in lowered concentration of the active centres for the methanation reaction.

Download Full-text

Study of potential oscillations during reaction of an aluminium single crystal with an aqueous KOH solution

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19900345 ◽

1990 ◽

Vol 55 (2) ◽

pp. 345-353 ◽

Cited By ~ 4

Author(s):

Ivan Halaša ◽

Milica Miadoková

Keyword(s):

Aqueous Solutions ◽

Single Crystal ◽

Single Crystals ◽

Periodic Potential ◽

Optimum Conditions ◽

Potential Oscillations ◽

Dilute Aqueous Solutions ◽

Experimental Findings ◽

Kinetics Of

The authors investigated periodic potential changes measured on oriented sections of Al single crystals during spontaneous dissolution in dilute aqueous solutions of KOH, with the aim to find optimum conditions for the formation of potential oscillations. It was found that this phenomenon is related with the kinetics of the reaction investigated, whose rate also changed periodically. The mechanism of the oscillations is discussed in view of the experimental findings.

Download Full-text