Boundary impurity segregation

A more sophisticated approach for determination of the grain boundary segregation is similar to the determination of the surface tension of silicon melt. The novel approach of surface tension simulation has been successfully implemented in the thermochemical database. Hence, the assessment of the parameters for impurity segregation in solid silicon phase may greatly extend the application of the thermochemical database. The calculation results for C and O segregation are shown as dashed lines in Fig. 13.28. The McLean segregation isotherm can be reproduced using the approach similar to the surface tension simulation. 

Solute and impurity segregation to grain boundaries in polycrystalline solids is known to affect mechanical properties and engineering performances of these materials. 

When M, equals MpjN in Eq. (11.8), the grain boundary mobility is the same as the pore mobility (equal mobility). The equal mobility condition on a grain size versus pore size plane can be calculated for any mechanism of pore migration. As an example, consider the pore migration controlled by surface diffusion. In this case the pore mobility Mp = D,, )l Ttr kT) and the boundary mobility M = Z) / r for boundaries without impurity segregation. If N is inversely proportional to the boundary area per grain and is expressed as the number of pores per atom at the boundary, ... 

As can be observed in Eq. (8), the impurity segregation at the grain boundaries not only justifies the existence of the threshold stress, but also provides data relating to the grain size and temperature dependence found experimentally. 

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