Oxygen Vacancies

Nanostructured TiO2 thin films were prepared by pulsed laser deposition (PLD) on indium-doped tin oxide (ITO) substrates. Results from X-ray photoelectron spectroscopy (XPS) show that Ti 2p core level peaks shift toward the lower binding energy with decrease in the buffer gas pressure (O-2:Ar= 1:1). This suggests that oxygen vacancies are created under insufficient oxygen conditions.............Combining the results from XPS and PEC studies, we conclude that the deposition pressure affects the concentration of the oxygen vacancies which changes the electronic structure of the TiO2. With reference to photoelectrochemical catalytic performance, our results suggest that it is possible to adjust the Fermi energy level and structure of TiO2 thin films by controlling the buffer gas pressure and temperature to align the energy of the flatband potential (V-fb) with respect to specific redox species in the electrolyte.

Photocatalytic activity of pulsed laser deposited TiO2 thin films, Elsevier BV, 2008


Introduction of Mg-impurities during crystal growth in a highly reducing atmosphere stimulates creation of F þ - centres (oxygen vacancy with one electron) needed for charge compensation of the Mg2þ-ion, which becomes negatively charged with respect to the lattice when it substitutes the Al3þ-ion. Subsequent aggregation of two defect pairs results in creation of a more complex aggregate defect denoted as the F22þ(2Mg)-centre. Detailed spectroscopic properties of this new colour centre was investigated recently by our group and published elsewhere(b).

Conclusion: Performance of a new Al2O3:C,Mg dosimetric material is determined by its defect structure by its electronic and optical properties. The crystals have deep stable traps of electrons and holes having a high capture-cross-section. Aggregate defects consisting of two oxygen vacancies and two Mg-impurities are believed to be responsible for the optical and radiation properties of the new material. Colour centres induced by radiation show strong absorption of stimulation light and have a short luminescence lifetime. The new material allows one to perform fast and no-destructive measurements of fluorescent signals.

a- NEW Al2O3:C,Mg CRYSTALS FOR RADIOPHOTOLUMINESCENT DOSIMETRY AND OPTICAL IMAGING; Radiation Protection Dosimetry (2006), Vol. 119, No. 1–4, pp. 218–221

b- Akselrod, M. S., Akselrod, A. E., Orlov, S. S., Sanyal, S. and Underwood, T. H. Fluorescent aluminum oxide crystals for volumetric optical data storage and imaging applications. J. Fluores. 13(6), 503–511 (2003)




Evans et al, Optical properties of lattice defects in a-Al2O3. Nucl. Instr. and Meth. in Phys. Res. B 91, 258–262.(1994).

Fluorescent aluminum oxide crystals for volumetric optical data storage and imaging
applications. J. Fluores. 13(6), 503–511 (2003).


Performance of a new Al2O3:C,Mg dosimetric material is determined by its defect structure and by its electronic and optical properties. The crystals have deep stable traps of electrons and holes having a high capture-cross-section. Aggregate defects consisting of two oxygen vacancies and two Mg-impurities are believed to be responsible for the optical and radiation properties of the new material. Color centers induced by radiation show strong absorption of stimulation light and have a short luminescence lifetime. The new material allows one to perform fast and nondestructive measurements of fluorescent signals.

NEW Al2O3:C,Mg CRYSTALS FOR RADIOPHOTOLUMINESCENT DOSIMETRY AND OPTICAL IMAGING



The solid solution of CeO 2-ZrO2 is used widely in automobiles as a three-way catalyst and an oxygen storage material. Many studies on this material have been conducted, and the reduced solid solution of CeO 2-ZrO2 having an equimolar composition of Ce and Zr (Ce / Zr = 50 / 50) has been confirmed to possess
a particularly excellent property for oxygen absorption/release [1–3]. Reduction treatment at high temperature, especially >1473 K, gives Ce 2Zr2O7 having a pyrochlore structure with an ordered arrangement of Ce and Zr ions along the <110>
direction, in which one-eighth of the oxygen in Ce 2Zr2O8 is released through the reduction [4]. The value of the oxygen deficiency parameter, or x in Ce2Zr2O7 + x, may change from 0 to 1 depending on the degree of reduction or oxidation. Recently,
the microstructural change associated with the absorption/release of oxygen is receiving much attention [4–7].


The three lattice images of Ce 2Zr2O7, Ce2Zr2O7.5 and Ce2Zr2O8 are all greatly different, and they can be characterized by the length of periodicity and the texture. The large change in the high-resolution lattice images evidently indicates the introduction and/or elimination of the oxygen vacancies, which means that the image is greatly affected by the vacancies. The TEM observation of oxygen vacancies was also reported by Shibahara et al. for M-Mn-O (M:La,Ba) oxide having perovskite structure [2-4]. However, in general, the contribution of oxygen defects to the highresolution images is very small. The image change observed in this study is exceptionally large and it may be used for determining the local amount of oxygen absorbed.


1 Microstructural investigation of ceria-zirconia solid solution with oxygen vacancies, Journal of Electron Microscopy 52(3): 309–312 2003
2 Shibahara H (1998) HREM and molecular dynamics studies of oxygen-defective LaMnO3 – x. J. Electron Microsc. 47: 327–333.
3 Shibahara H, Numaguchi K, Kawasaki M, Takizawa H, Oikawa T, and Taguchi H (1995) Quantification of oxygen vacancies in perovskite using a 300 kV HREM with an imaging plate. J. Electron Microsc. 44: 174–181.
4 Shibahara H, Kawasaki M, and Taguchi H (1993) Detection of oxygen vacancies in BaMnO 3 – x with 200 kV electron-microscopes. J. Electron Microsc. 42: 211–217.



Incoherent imaging and analysis techniques in the scanning transmission electron microscope (STEM) provide the potential to map changes in structure, composition and bonding that occur at materials interfaces and defects on the fundamental atomic scale. Such comprehensive characterization capabilities permit a detailed analysis of the structure-property relationships of interfaces and defects to be performed. In this paper, we discuss the resolution limits of such techniques in the JEOL 2010F STEM/TEM operating both under standard conditions and at elevated temperatures. Examples of the use of such techniques to quantify the atomic scale defect chemistry at interfaces and defects in perovskite oxides, the growth and structure of II-VI and III-V quantum dots and the electronic structure of threading dislocations in GaN will also be presented.

Application of atomic scale STEM techniquesto the study of interfaces and defects in materials , Journal of Electron Microscopy 50:205-218 (2001)




Quantification of Oxygen Vacancies in Perovskite using a 300 kV HREM with an Imaging Plate

The structural determination and quantification of oxygen vacancies in LaMnO3–x were carried out in a 300 kV HREM equipped with an imaging plate. On the basis of direct observation with HREM and the aid of computer simulation, optimum imaging conditions were found, where oxygen atoms and the vacancies are imaged as bright spots in a "dark-spot image." Under the optimum imaging conditions, the dependence of image contrast on the atomic occupancies of the oxygen sites and the thickness of the samples is discussed on the basis of dynamical diffraction theory. Using an imaging plate, the atomic occupancies were quantitatively estimated from the intensity distributions of the bright spots in the observed image contrast.


The stability of an oxygen-defective structure of LaMnO3–x was studied by MD simulation. The relaxed structure based on the MD simulation could provide sufficient adequate information to discuss the proposed structure model of LaMnO3–x compared with the observed image contrast by HREM. Image calculation of the relaxed structure by the multislice method also supported the proposed defect structure model. Analysis of the atomic structure by MD simulation gave the information of oxygen ion and cation migration in oxygen-defective perovskite.

HREM and molecular dynamics studies of oxygen-defective LaMnO3–x



Defect-enhanced electron field emission from chemical vapour deposited diamond, 1995

Diamond samples with varying defect densities have been synthesized by chemical vapour deposition, and their field emission characteristics have been investigated. Vacuum electron field emission measurements indicate that the threshold electric field required to generate sufficient emission current densities for flat panel display applications (>lO mA/cm”) can be significantly reduced when the diamond is grown so as to contain a substantial number of structural defects.