Oxygen vacancies creation

According to all these considerations, the oxygen vacancy creation within the perovskite material at high cathodic polarization can be described by the following reaction... 

The addition of a dopant oxide gives rise to the creation of oxygen vacancies which are responsible for the ionic conductivity in these materials. Most work... 

Creation of intrinsic donors by lattice defects (for instance oxygen vacancies or metal atoms on interstitial lattice sites) or... 

Creation and control of intrinsic donor levels by defects such as oxygen vacancies or Zn atoms on interstial sites. Undoped ZnO fdms with resistivities of less than 5x10 Qcm have been prepared by magnetron sputtering without adding impurities but were found to be unstable at T > 150... 

However, there are exceptions to this rule, when a cation-cation bond across the vacancy site may be formed. This is the case in bulk Si02, where the creation of an oxygen vacancy breaks two 0-Si bonds. The atomic displacements of the two neighbouring silicon atoms are directed inwards in such a way that the Si-Si distance across the vacancy site is reduced by about 0.5 A with respect to its value in the perfect oxide [256]. 

Fig. 3. Schematic model for the creation of oxygen vacancies on Ti02 (110) by combination of bridging hydroxyl groups to form water. M.A. Henderson, Journal of Physical Chemistry B, V. 101 (1997). Reproduced by permission of the American Chemical Society.

The mixture of these effects described above is obtained by the doping of rare earths elements with variable oxidation state. For example, incorporation of terbium or praseodymium increases both oxygen desorption at lower temperatures and the creation of oxygen vacancies than those of pure ceria. The former is due to the lower binding energy of a lattice oxygen in the mixed oxides and the latter is to the existence of irivalent terbium and praseodymium ions. In addition, a similar effect is also provided by the ternary oxides Cco6Zro4.iM 02. >2 (M = La, and Ga ), ... 

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