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Vacancies and conduction

By noting the relationships between concentrations of anion vacancies and conduction-band electrons, the dependence of electrical conductivity k on oxygen partial pressure can be derived as before. These are shown in Equations (3.12),... [Pg.45]

When a specific binary material is considered, we will need to add to the list of all internal disorder reactions (which all occur in that material even though with differing weight) a single external one (which we have already included in Table 5.2, page 162). Without restriction of generaUly we wiU select for our model compound MX the formulation with anion vacancies and conduction electrons, i.e. [Pg.164]

Nk is positive for interstitial oxygen defects and holes (k = O" and h ), and negative for oxygen vacancies and conduction electrons (k = Vq and e ). This can be generalized to the following intelligible theorem (referred to below as the P theorem ) ... [Pg.168]

Ionic conductivity is used in oxygen sensors and in batteries (qv). Stabilized zirconia, Zr Ca 02 has a very large number of oxygen vacancies and very high conductivity. P-Alurnina/72(9(9j5 -4< -(y, NaAl O y, is an excellent cation conductor because of the high mobiUty of Na" ions. Ceramics of P-alurnina are used as the electrolyte in sodium-sulfur batteries. [Pg.309]

Shock-modified rutile is found to exhibit two characteristic resonances, which can be confidently identified as (1) an isotropic resonance characteristic of an electron trapped at a vacancy, and (2) an isotropic resonance characteristic of a Ti" interstitial. The data indicate a concentration of 2 X 10 cm , which is an order of magnitude greater than observed in hydrogen- or vacuum-induced defect studies. At higher pressures the concentration of interstitials is the same as at lower pressure, but more dispersion is observed in the wave shape, indicating higher microwave conductivity. [Pg.166]

The electrical conductivity is proportional to n. Equation 1.168 therefore predicts an electrical conductivity varying as p. Experimental results show proportionality to p and this discrepancy is probably due to incomplete disorder of cation vacancies and positive holes. An effect of this sort (deviation from ideal thermodynamic behaviour) is not allowed for in the simple mass action formula of equation 1.167. [Pg.255]

Although this is a small fraction, for 1 mole of lattice sites, this amounts to 5.6 X1018 Schottky defects. The ability of ions to move from their sites into vacancies and by so doing creating new vacancies is largely responsible for the conductivity in ionic crystals. [Pg.241]

The high-pressure region is associated with the electroneutrality equation [h ] = 2[V ]. Holes predominate, so that the material is a p-type semiconductor in this regime. In addition, the conductivity will increase as the g power of the partial pressure of the gaseous X2 component increases. The number of metal vacancies (and nonmetal excess) will increase as the partial pressure of the gaseous X2 component increases and the phase will be distinctly nonstoichiometric. There is a high concentration of cation vacancies that would be expected to enhance cation diffusion. [Pg.336]

An example of a layer structure mixed conductor is provided by the cathode material L CoC used in lithium batteries. In this solid the ionic conductivity component is due to the migration of Li+ ions between sheets of electronically conducting C0O2. The production of a successful mixed conductor by doping can be illustrated by the oxide Cei-jPxx02- Reduction of this solid produces oxygen vacancies and Pr3+ ions. The electronic conductivity mechanism in these oxides is believed to be by way of electron hopping between Pr4+ and Pr3+, and the ionic conductivity is essentially vacancy diffusion of O2- ions. [Pg.394]

In comparison to the research in n-type oxide semiconductors, little work has been done on the development of p-type TCOs. The effective p-type doping in TCOs is often compensated due to their intrinsic oxide structural tolerance to oxygen vacancies and metal interstitials. Recently, significant developments have been reported about ZnO, CuA102, and Cu2Sr02 as true p-type oxide semiconductors. The ZnO exhibits unipolarity or asymmetry in its ability to be doped n-type or p-type. ZnO is naturally an n-type oxide semiconductor because of a deviation from stoichiometry due to the presence of intrinsic defects such as Zn interstitials and oxygen vacancies. A p-type ZnO, doped with As or N as a shallow acceptor and codoped with Ga or Zn as a donor, has been recently reported. However, the origin of the p-type conductivity and the effect of structural defects on n-type to p-type conversion in ZnO films are not completely understood. [Pg.484]

The activation energy for oxide ion conduction in the various zirconia-, thoria- and ceria-based materials is usually at least 0.8 eV. A significant fraction of this is due to the association of oxide vacancies and aliovalent dopants (ion trapping effects). Calculations have shown that the association enthalpy can be reduced and hence the conductivity optimised, when the ionic radius of the aliovalent substituting ion matches that of the host ion. A good example of this effect is seen in Gd-doped ceria in which Gd is the optimum size to substitute for Ce these materials are amongst the best oxide ion conductors. Fig. 2.11. [Pg.39]


See other pages where Vacancies and conduction is mentioned: [Pg.175]    [Pg.207]    [Pg.18]    [Pg.175]    [Pg.207]    [Pg.18]    [Pg.2205]    [Pg.645]    [Pg.447]    [Pg.355]    [Pg.359]    [Pg.360]    [Pg.246]    [Pg.153]    [Pg.460]    [Pg.26]    [Pg.245]    [Pg.536]    [Pg.311]    [Pg.95]    [Pg.421]    [Pg.431]    [Pg.437]    [Pg.256]    [Pg.481]    [Pg.140]    [Pg.246]    [Pg.3]    [Pg.7]    [Pg.10]    [Pg.15]    [Pg.22]    [Pg.29]    [Pg.39]    [Pg.4]    [Pg.8]    [Pg.25]    [Pg.64]    [Pg.208]    [Pg.267]    [Pg.414]    [Pg.616]   
See also in sourсe #XX -- [ Pg.28 , Pg.29 ]




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