Vacancy generation

In doped ceria, the concentration of oxygen vacancies is almost constant because the concentration of oxygen vacancies generated by Equation (1.14) is negligible compared with that generated by Equation (1.19) see also Equation (1.1) ... 

He found that these zeolites were hydrophobic and attributed this to the absence of silanol groups and the formation of Si-O-Si bonds in the vacancies generated by dealumination. 

The (3-oxygens in the surface lattice of two series of perovskites can only be desorbed at high temperature (T>700 °C) leading to the B-site ion reduction and, surface anion vacancy generation. 

Investigations of the generation of super base sites on alkaline earth metal oxides by doping with alkali metals (246,247,253) led to the inference that when zero-valent alkali metals react with a metal oxide surface, the electron donated by the alkali metal to the oxide lattice resides in a defect site, such as an oxygen vacancy, generating a one-electron donor site (F center) (254,255) (Scheme 40). 

Next let us discuss the electronic defects associated with point defects in semiconductive or insulating compounds, which lead to non-stoichiometry. Consider a NiO crystal, which has a NaCl-type structure, as NiO can be regarded as an ionic crystal, the valence states of Ni and O are Ni and O , respectively. We assume that the non-stoichiometry originates only from metal vacancies. Generation of metal defects in NiO may be expressed by a chemical reaction similar to eqn (1.119), i.e. 

In the Kirkendall effect, the difference in the fluxes of the two substitutional species requires a net flux of vacancies. The net vacancy flux requires continuous net vacancy generation on one side of the markers and vacancy destruction on the other side (mechanisms of vacancy generation are discussed in Section 11.4). Vacancy creation and destruction can occur by means of dislocation climb and is illustrated in Fig. 3.36 for edge dislocations. Vacancy destruction occurs when atoms from the extra planes associated with these dislocations fill the incoming vacancies and the extra planes shrink (i.e., the dislocations climb as on the left side in Fig. 3.36 toward which the marker is moving). Creation occurs by the reverse process, where the extra planes expand as atoms are added to them in order to form vacancies, as on the right side of Fig. 3.36. This contraction and expansion causes a mass flow that is revealed by the motion of embedded inert markers, as indicated in Fig. 3.3 [4]. 

Additional work is needed to refine these models. For example, rapid vacancy generation and vacancy-interstitial recombination are assumed. These effects combine to modulate the self-interstitial supersaturation. Thus, the supply of self-interstitials at the oxidizing interface cannot keep up with recombination effects. Rapid recombination may be justified at high doping levels, because species such as V+ and I or V and I+ may be plentiful. 

The vacancy generated is then available to recombine with a Si self-interstitial produced by oxidation ... 

The formation of this ethyl complex can be rationalized assuming that the vacancy generated by the insertion step migrates to the position labilized by the large trans effect of the alkyl group. Actually, this position lies at the other extreme of the molecule, as a result of the transmission of the trans effect through the bridging hydride. 

Energies of the vacancy generation Ey and vacancy diffusion Uy in crystal lattice turn out to be a controlling factor of a material resistance to strain at high temperatures. These factors are affected by strength of interatomic bonding. 

Diffusion parameters the energy of the vacancy generation and the energy of the vacancy diffusion L/y. 

Chao et al. [1981] Cation/anion conductors Constrained by Esaki tunneling Cation injection from metal or anion vacancy generation at the m/bl interface No Yes Not addressed... 

---