Oxygen vacancy concentrations

Figure 26. Predictions of the Adler model shown in Figure 25 assuming interfacial electrochemical kinetics are fast, (a) Predicted steady-state profile of the oxygen vacancy concentration ( ) in the mixed conductor as a function of distance from the electrode/electrolyte interface, (b) Predicted impedance, (c) Measured impedance of Lao.6Cao.4Feo.8-Coo.203-(5 electrodes on SDC at 700 °C in air, fit to the model shown in b using nonlinear complex least squares. Data are from ref 171.

Figure 7.4 Oxygen vacancy concentration in Cu20 calculated as described in the text at three different oxygen pressures. The dashed lines for the two lower pressures indicate the temperature region where Cu20 is thermodynamically unfavored relative to Cu as defined in the phase diagram in Fig. 7.3.

A numerical model to simulate the lattice expansion behavior of the doped lanthanum chromites under a cell operating condition has been proposed, and the deformation of the lanthanum chromite interconnectors has been calculated [33], In the model, the sample deformation is calculated from the profile of the oxygen vacancy concentration in the interconnector. Under a practical cell operation, the oxygen vacancy concentration in the interconnector distributes unevenly from the air side to the fuel side. The distribution of the oxygen vacancy concentration in the interconnector depends on both the temperature distribution in the interconnector and the profile of the oxygen partial pressure at the interconnector surface. Here, a numerical model calculation for the expansion behavior of the LaCrC>3 interconnector under a practical cell operation is carried out, and the uneven distribution of... 

Calculation of the oxygen vacancy concentration at the interconnector surface On the basis of the point defect theory, the oxygen vacancy concentration (mole fraction) 8 on the fuel and air side surfaces of the interconnector are calculated [34], In an equilibrium state, the formation of the oxygen vacancy can be described as follows using Kroger-Vink notation [35] ... 

Calculation of the distribution of the oxygen vacancy concentration in the interconnector... 

Pa < p0z < 105Pa (BD) The oxygen vacancy concentration now determined by the acceptor impurity concentration [A ], is little affected by changes in Po2 and remains sensibly constant. It follows from Eq. (2.49) that... 

Fig. 2. (a) Sketch of the relations between defect concentrations and partial pressure (Brouwer diagram) of a pure oxide MO In regime II the intrinsic Schottky disorder determines the concentration, whereas in I and III non-stoichiometry prevails, (b) Dependence of the hole and electron concentration on the frozen-in oxygen vacancy concentration in a negatively (acceptor) doped oxide. 

The same happens with the oxygen sublattice when we typically go below 600 K, then also the oxygen vacancy concentration becomes invariant and only electronic transfer reactions are reversible. The ion defect concentration remains on a high level with unexpectedly high ion conduction at low temperatures (see Fig. 14).63... 

Four different routes were employed for the synthesis of iron-oxide-based redox water-sphtting materials Solid-State Synthesis (SSS), Self-Propagating High-Temperature Synthesis (SHS), Gel Combustion (GC) and Aerosol Spray Pyrolysis (ASP) [8]. These synthesis methods were chosen with the rationale to exploit particular characteristics of each one for the synthesis of products with tunable oxygen vacancies concentration. The synthesis details have been reported previously [8], therefore only the general reaction concepts are reported below, where A and B denote the bivalent dopant metals Ni, Mn or Zn. 

Ceria-based catalysts are intensively used because of their high chemical and physical stability, high oxygen mobility and high oxygen vacancy concentrations, which are characteristic of fluorite-type oxides. The possibility of cycling easily between reduced and oxidized states (Ce Ce" ) permits the reversible addition... 

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