On the origin of defect states in calcium tungstate

1969 ◽  
Vol 47 (4) ◽  
pp. 463-471 ◽  
Author(s):  
M. Sayer ◽  
A. D. Souder
Keyword(s):  
Ionizing Radiation ◽  
Single Crystals ◽  
Oxygen Vacancies ◽  
Excitation Mechanism ◽  
Defect States ◽  
Thermally Stimulated Current ◽  
Calcium Tungstate ◽  
Monovalent Ions ◽  
Monovalent Ion ◽  
Electron And Hole Traps

A comparison has been made of thermoluminescence and thermally stimulated current in single crystals of calcium tungstate either doped with impurities or nominally pure but excited by ionizing radiation. Both effects were large in the case of monovalent impurities with glow peaks near 260 °K being characteristic of the impurity and peaks near 160 °K arising from an enhancement of a structure which normally results from radiation damage. Trivalent impurities had a lesser effect with the production of glow peaks near 300 °K. The structures responsible for the prominent glow peaks are suggested to be: 260 °K—monovalent ions in calcium sites, 154/160 °K—oxygen vacancies associated with either a W5+ or a monovalent ion at a calcium site, 300 °K—calcium vacancies. The occupancy of electron and hole traps is found to be related. This relationship is used to deduce information regarding the excitation mechanism for free holes and electrons in calcium tungstate.

Deformation by slip in single crystals of calcium tungstate

1964 ◽  
Vol 9 (102) ◽  
pp. 911-916 ◽  
Author(s):  
B. Cockayne ◽  
G. E. Hollox
Keyword(s):  
Single Crystals ◽  
Calcium Tungstate

Ionization of High-Density Deep Donor Defect States Explains the Low Photovoltage of Iron Pyrite Single Crystals

2014 ◽  
Vol 136 (49) ◽  
pp. 17163-17179 ◽  
Author(s):  
Miguel Cabán-Acevedo ◽  
Nicholas S. Kaiser ◽  
Caroline R. English ◽  
Dong Liang ◽  
Blaise J. Thompson ◽  
...  
Keyword(s):  
Single Crystals ◽  
High Density ◽  
Iron Pyrite ◽  
Defect States ◽  
Deep Donor ◽  
Donor Defect

scholarly journals Identification of electron and hole traps in lithium tetraborate (Li2B4O7) crystals: Oxygen vacancies and lithium vacancies

2010 ◽  
Vol 107 (11) ◽  
pp. 113715 ◽  
Author(s):  
M. W. Swinney ◽  
J. W. McClory ◽  
J. C. Petrosky ◽  
A. T. Brant ◽  
V. T. Adamiv ◽  
...  
Keyword(s):  
Oxygen Vacancies ◽  
Lithium Tetraborate ◽  
Electron And Hole Traps

scholarly journals Dispersion of Defects in TiO2 Semiconductor: Oxygen Vacancies in the Bulk and Surface of Rutile and Anatase

Catalysts ◽  
2020 ◽  
Vol 10 (4) ◽  
pp. 397 ◽  
Author(s):  
Mohammadreza Elahifard ◽  
Mohammad Reza Sadrian ◽  
Amir Mirzanejad ◽  
Reza Behjatmanesh-Ardakani ◽  
Seyedsaeid Ahmadvand
Keyword(s):  
Active Site ◽  
Active Sites ◽  
Oxygen Vacancies ◽  
Oxygen Deficiency ◽  
Rutile Phase ◽  
Unit Cell ◽  
Defect States ◽  
Defect Band ◽  
O Vacancy ◽  
Double Cluster

Oxygen deficiency (O-vacancy) contributes to the photoefficiency of TiO2 semiconductors by generating electron rich active sites. In this paper, the dispersion of O-vacancies in both bulk and surface of anatase and rutile phases was computationally investigated. The results showed that the O-vacancies dispersed in single- and double-cluster forms in the anatase and rutile phases, respectively, in both bulk and surface. The distribution of the O-vacancies was (roughly) homogeneous in anatase, and heterogenous in rutile bulk. The O-vacancy formation energy, width of defect band, and charge distribution indicated the overlap of the defect states in the rutile phase and thus eased the formation of clusters. Removal of the first and the second oxygen atoms from the rutile surface took less energy than the anatase one, which resulted in a higher deficiency concentration on the rutile surface. However, these deficiencies formed one active site per unit cell of rutile. On the other hand, the first O-vacancy formed on the surface and the second one formed in the subsurface of anatase (per unit cell). Supported by previous studies, we argue that this distribution of O-vacancies in anatase (surface and subsurface) could potentially create more active sites on its surface.

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