Grain Boundaries Flux Lines

The driving forces necessary to induce macroscopic fluxes were introduced in Chapter 3 and their connection to microscopic random walks and activated processes was discussed in Chapter 7. However, for diffusion to occur, it is necessary that kinetic mechanisms be available to permit atomic transitions between adjacent locations. These mechanisms are material-dependent. In this chapter, diffusion mechanisms in metallic and ionic crystals are addressed. In crystals that are free of line and planar defects, diffusion mechanisms often involve a point defect, which may be charged in the case of ionic crystals and will interact with electric fields. Additional diffusion mechanisms that occur in crystals with dislocations, free surfaces, and grain boundaries are treated in Chapter 9. 

In NbsSn superconductors the flux lines are pinned by the grain boundaries in the Nb3Sn filaments. The dependence of the effective volume pinning force Fp on the grain size is shown in Fig. 4.2-14. This leads to the requirement that the reaction temperature is optimized not... 

In most polycrystalline thin films, columnar grains typically span the thickness of the film. When a metal stripe or line is patterned from a thin film, there is a continuous network of grain boundaries along the direction of current-induced atomic flux, if the width of the lines is larger than the grain... 

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