Mobility defect

From polarization curves the protectiveness of a passive film in a certain environment can be estimated from the passive current density in figure C2.8.4 which reflects the layer s resistance to ion transport tlirough the film, and chemical dissolution of the film. It is clear that a variety of factors can influence ion transport tlirough the film, such as the film s chemical composition, stmcture, number of grain boundaries and the extent of flaws and pores. The protectiveness and stability of passive films has, for instance, been based on percolation arguments [67, 681, stmctural arguments [69], ion/defect mobility [56, 57] and charge distribution [70, 71]. 

After thermalization, the defects begin to migrate, recombine, cluster, or precipitate provided the temperature is high enough to activate the motion of point defects. The various possible processes depend on defect concentration and their spatial distribution as well as on defect mobility and their interaction energies. As in non-metallic crystals, internal and external surfaces act as sinks for at least a part of the radiation induced defects in metals. 

R.W. Balluffi. Vacancy defect mobilities and binding energies obtained from annealing studies. J. Nucl. Mats., 69-70 240-263, 1978. 

The conclusion could be drawn from Fig. 4.2 that the steady-state profile depends essentially on the defect mobility or temperature - unlike the black sphere model, equation (4.1.70). The steady-state solution y(r) defines the stationary reaction rate K(00) through the effective radius of reaction R n-... 

Kinetics of the tunnelling recombination depends greatly upon the defect mobility (whether a static tunnelling luminescence regime at low temperatures or the diffusion-controlled regime arising at higher temperatures when defects become mobile) and their spatial distribution. 

In calculations presented below we assume first one kind of defects to be immobile (Da = 0, k = 0) and their dimensionless initial concentration n(0) = 0.1 is not too high it is less than 10 per cent of the defect saturation level accumulated after prolonged irradiation [41]. Its increase (decrease) does not affect the results qualitatively but shorten (lengthen, respectively) the distinctive times when the effects under study are observed. To stress the effects of defect mobility, we present in parallel in Sections 6.3.1 and 6.3.2 results obtained for immobile particles A (D = 0, asymmetric case) and equal mobility of particles A and B (Da = Dq, symmetric case). In both cases only pairs of similar particles BB interact via elastic forces, (6.3.5), but not AA or AB. The initial distribution (t = 0) of all defects is assumed to be random, Y(r > 1,0) = -X (r,0) = 1 i/ = A,B. 

In this Chapter the kinetics of the Frenkel defect accumulation under permanent particle source (irradiation) is discussed with special emphasis on many-particle effects. Defect accumulation is restricted by their diffusion and annihilation, A + B — 0, if the relative distance between dissimilar particles is less than some critical distance 7 0. The formalism of many-point particle densities based on Kirkwood s superposition approximation, other analytical approaches and finally, computer simulations are analyzed in detail. Pattern formation and particle self-organization, as well as the dependence of the saturation concentration after a prolonged irradiation upon spatial dimension (d= 1,2,3), defect mobility and the initial correlation within geminate pairs are analyzed. Special attention is paid to the conditions of aggregate formation caused by the elastic attraction of particles (defects). 

Hahm J, Sibener SJ (2001) Time-resolved atomic force microscopy imaging studies of asymmetric PS-b-PMMA ultrathin films dislocation and disclination transformations, defect mobility, and evolution of nanoscale morphology. J Chem Phys 114(10) 4730-4740... 

In concluding this section, we note that defect calculations may be used to study defect mobilities as well as defect formation and interaction processes. Assuming the validity of the hopping model of defect transport the frequency of defect jumps can then be written as ... 

Table 2.5. Elccuonic and oxygen defect mobilities of ceria-bosed materials at 1273K.

There is evidence supporting both of these. However, in view of our earlier remarks we can postulate another more general mechanism, which should apply at temperatures where defect mobility in the surface and subsurface layers of a catalyst is significant (i.e., at temperatures >0 25 of the catalyst). Both reactants are assumed to be chemisorbed, but the reaction step is now initialed by the defect appearing at an appropriate point underneath the other reactant. One then obtains the rather naive picture of the process as one by which the active reactant pushes the other off the surface as a product molecule. This would certainly provide more favourable steric conditions for the reaction path. Let us exanaine one or two catalytic reactions on this basis. 

We can put these questions another way is the driving force due to a gradient in the chemical potential or in the electrochemical potential It is important to remember that phase diagrams describe the equilibrium state. Phase transformations occur because the system is not in its equilibrium state. We can change P, T, or c and then examine how long it takes to reach equilibrium and how we can get there. Our main tool will be our understanding of point defect mobility and diffusion. In general, we will... 

Such behavior might be caused by lower defect mobility, which would weaken the ionic behavior of the material. 

The method to determine defect concentrations, defect mobilities, and their influence on the diffusion is to use conductivity measurements at different temperatures and measuring frequencies. In a single experiment the activation energies for formation and displacement of the defects can be established if both the intrinsic and extrinsic domain can be covered. Some defects can be identified spectroscopically, e.g., with electron paramagnetic resonance (EPR or ESR) if the defect has unpaired electrons. 

---