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Anion Vacancies (anion + vacancy)

Distribution by Scientific Domains
Physics and Astronomy50%

Selected Abstracts

First-Principles Calculations of Anion Vacancies in Oxides and Nitrides

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002
Isao Tanaka
The formation energy, structural relaxation, and defect-induced states of neutral anion vacancies of five oxides (i.e., MgO, Al2O3, ZnO, In2O3, and SnO2) and four nitrides (i.e., AlN, Si3N4, Ge3N4, and InN) are systematically discussed, based on first-principles plane-wave pseudopotential calculations. Two types of polymorphs for each compound are compared. The number of atoms included in the supercells ranged from 54 to 96. When a localized vacancy-induced state appears within the band gap, as in a typical ionic crystal, the formation energy can be well scaled by the band gap of the perfect crystal. On the other hand, when an empty and localized vacancy-induced state is located above the highest occupied band or no localized state is formed, the formation energy has a tendency to be smaller. In compounds such as ZnO and SnO2, the formation energy is dependent largely on the crystal structure. This result can be explained by the transition of the vacancy-induced state from occupied to unoccupied, which is caused by the change in atomic arrangement, as represented by the cation coordination number. [source]

A TEM study on ZrO2 -rich phases in the quasibinary system ZrO2 -Zr3N4: Comparison between fast and slowly cooled samples

CRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2005
A. T. Tham
Abstract A thorough comparison between the slowly and fast cooled ,,-type oxynitrides of zirconium has been carried out by means of transmission electron microscopy. This work aims at detecting and analyzing the so-called "modulated" ,, phase, which has been involved in the introduction of ordered anion vacancies through nitridation of zirconia. The gained information from the occurrence of such a modulated phase and the manner, in what it appears, do support the suggested structure model, which had been developed in early works in order to get a better understanding of the typical phase transitions in zirconium oxynitrides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

First-Principles Calculations of Anion Vacancies in Oxides and Nitrides

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 1 2002
Isao Tanaka
The formation energy, structural relaxation, and defect-induced states of neutral anion vacancies of five oxides (i.e., MgO, Al2O3, ZnO, In2O3, and SnO2) and four nitrides (i.e., AlN, Si3N4, Ge3N4, and InN) are systematically discussed, based on first-principles plane-wave pseudopotential calculations. Two types of polymorphs for each compound are compared. The number of atoms included in the supercells ranged from 54 to 96. When a localized vacancy-induced state appears within the band gap, as in a typical ionic crystal, the formation energy can be well scaled by the band gap of the perfect crystal. On the other hand, when an empty and localized vacancy-induced state is located above the highest occupied band or no localized state is formed, the formation energy has a tendency to be smaller. In compounds such as ZnO and SnO2, the formation energy is dependent largely on the crystal structure. This result can be explained by the transition of the vacancy-induced state from occupied to unoccupied, which is caused by the change in atomic arrangement, as represented by the cation coordination number. [source]

Defects in Ce3+ doped Y2SiO5

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 1 2005
T. Aitasalo
Abstract The crystal defects in the Ce3+ doped X2 -type yttrium oxyorthosilicate, X2 -Y2SiO5:Ce3+, were studied by high-resolution time-resolved laser excited photoluminescence (PL), thermoluminescence (TL) and EPR spectroscopy. X2 -Y2SiO5:Ce3+ shows two strong 5d1,4f1 emission bands with maxima at about 395 (25300) and 430 nm (23250 cm,1) with ca. 40 ns decay times. In addition, two very weak emission bands at 484 (20660) and 577 nm (17330 cm,1) under wide band UV excitation (maximum at 360 nm) from a pulsed Xe lamp can be observed with decay times in the millisecond range. Under the third harmonic of a Nd:YAG laser (355 nm) excitation these bands are split into a number of sharper bands. The EPR shows the presence of electrons occupying anion vacancies in Y2SiO5 lattice while thermoluminescence revealed the presence of two different traps which are, however, too deep for efficient persistent luminescence materials. The defects play a crucial role in the creation of the Ce3+,Ce4+ charge transfer luminescence. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]