Grain-Boundary Mobility

Germanium, an isovalent impurity in Si, is concentrated at grain boundaries and eliminates dangling bonds, without changing the coordination number of the lattice site. Ge atoms form covalent bonds with Si atoms and inhibit recrystallization owing to the formation of low-mobility grain boundaries. 

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]. 

The mobility, M, is a function of the substance, and obeys an AiThenius expression M — Mq exp —(AE/RT) where AE is the energy of transfer across the grain boundary. 

The mobility of grain boundaries is substantially reduced by the presence of the pores and the resn aiiiiiig force may be calculated simply to have a maximum value. 

This easier redueibility of the in the grain boundaries would also be the result of a higher oxygen mobility in these highly defective zones. 

Royer, S Duprez, D Kaliaguine, S. Role of bulk and grain boundary oxygen mobility in the catalytic oxidation activity of LaCoi. Fe Os, J. Catal, 2005, Volume 234, Issue 2, 364-375. 

During the experiment the boundary displacement is recorded. Its derivative with regard to time is the velocity v of grain boundary motion, which is related to the driving force p by the boundary mobility m = v p. For convenience we use the reduced boundary mobility... 

As was already shown in the past, for instance by Aust and Rutter or Shvindlerman et al. - the mobility of tilt grain boundaries depends on axis and angle cp of... 

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