Oxygen interstitials

AUan N L and W C Mackrodt 1994. Oxygen Interstitial Defects in High-T Oxides. Molecular Simnlat 12 89-100. 

This is the same as saying that two Cu3+ ions are created per oxygen interstitial ... 

At higher oxygen partial pressures, assume that oxygen is incorporated into the structure and adds to the oxygen interstitials already present as part of the Frenkel equilibrium. The incorporation of neutral oxygen requires the abstraction of two electrons to form oxide ions, thus generating an equal number of holes ... 

Equation (8.1c) is derived from Eq. (8.1b) by supposing that the oxygen interstitials are lost to the atmosphere ... 

These charges exactly balance, and the material would be an insulator, a normal ionic compound. Hole doping can be achieved by adding lower valence cation such as Sr2+ or oxygen interstitials to the charge reservoir. For Sr2+ aceptor dopants ... 

The charge difference between the charge reservoir and the superconducting layers must be achieved by the addition of balancing charges, xh in this case. For oxygen interstitials ... 

Slope = 1/5.5. The equation is in agreement with holes plus oxygen interstitials ... 

Between the two possible defects which may be responsible for hyperstoichiometry (i.e. uranium interstitials or oxygen vacancies) the latter is well evidenced by measurements of lattice parameter and densityand neutron diffraction Oxygen interstitials order in U4O9 to provide a crystal structure which can be derived from the fluorite structure of U02+x-... 

The negative charge (with respect to the lattice) of oxygen interstitials (0 ) is balanced by the oxidation of to either or (more unlikely)... 

Oxygen interstitials of the two types as well as oxygen vacancies are associated in different ways, forming clusters. Proposed clusters are (Vq = oxygen vacancy) ... 

In conclusion, electron microscopy techniques reveal considerable evidence for variability in composition and defect structures, such as cation and anion vacancies, extended defects, substitutional ions and oxygen interstitials these are common to all of the high temperature superconducting oxides. These defects play an important role in controlling the carrier concentrations and therefore the... 

Point defects are also highly prominent in the Tl,Pb,Bi/Ba,Sr,-Ca/Cu/O superconductors. Cation vacancies frequently occur. Some T1 is found on Ca sites, and there is evidence for Ca on the Sr/Ba site. Some Bi is found on both Sr and Ca sites. Both oxygen interstitials and vacancies apparently can occur. Present evidence suggests that compounds with the ideal structures and compositions would not be metallic or superconducting. There are also strong indications that these materials at their ideal compositions are in fact too unstable to be prepared. 

Figure 6.5. ED in (001) of (a) O2-annealed 2212 and (c) the HRTEM modulated image—the atom columns are shown with an incommensurate (modulated) structure, (c) N2-annealed with 2212. (Temperature of anneal 400 °C.) (d) its HRTEM image (/ , d) show the commensurate structure, (e) Changes in magnetic flux inclusion annealed in (a) N2 (b) in oxygen. The resulting changes in the electronic structure due, e.g., to oxygen interstitials, influence the catalytic process, (f) (001) CBED of sample annealed in oxygen. HOLZ is arrowed. (After Gai J. Solid State Chem. 104 119.)...

This is the general expression for the equilibrium constant of oxygen interstitials in Y2O3. 

Mass of contents for oxygen interstitial [(4x55.85)+(4x16.00x1/0.910)]/(Aax10 ) giving a density of 6.2126x10 kg... 

At high oxygen partial pressures an equilibrium is established between the gas phase oxygen, interstitial oxygen ions and electron holes and conductivity is predominantly p-type due to electron-hole transfer. 

Fig. 1.14. Dumbbell oxygen interstitial defects in ZnO in comparison to the ideal lattice structure and the octahedral oxygen interstitial [114,115]. The structure of the rotated dumbbell interstitial depends on the charge state. Copyright (2005) by the American Physical Society...

The electron concentration in donor-doped TCOs becomes compensated with increasing oxygen partial pressure. The nature of the compensating defect thereby depends on the material. As mentioned earlier, compensation of n-type doping in ZnO occurs by introduction of zinc vacancies. In contrast, compensation in 1 03 is accomplished by oxygen interstitials [117], Their importance in Sn-doped 1 03 has been already pointed out by Frank... 

Fig. 1.15. Electron concentration (dashed line) of Sn-doped indium oxide and Al-doped ZnO in dependence on oxygen partial pressure for a dopant concentration of 1 % [117]. With increasing oxygen partial pressure the donors become compensated by oxygen interstitials (In20s) or by zinc vacancies (ZnO). Reprinted with permission from [117]. Copyright (2007) by the American Physical Society...

Self-diffusion in materials occurs by repeated occupation of defects. Depending on the defects involved one can distinguish between (1) vacancy, (2) interstial, and (3) interstitialcy mechanisms [107], As an example, different diffusion paths for oxygen interstitials are illustrated in Fig. 1.16 [129]. For a detailed description of diffusion paths for oxygen vacancies, zinc vacancies and zinc interstitials the reader is also referred to literature [129,130]. 

Fig. 1.16. Diffusion paths accessible to oxygen interstitials on the wurtzite lattice...

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