Chemistry dependence of the grain boundary character distribution (GBCD) of olivine

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The grain boundary character distribution (GBCD) is a measure of the natural frequency of different grain boundaries; it is anisotropic and scale invariant for polycrystals without crystal preferred orientations. Based on these observations it was concluded that the GBCD is an intrinsic parameter related to the crystal structure. The GBCD gives the full 5 parameters needed to describe the geometry of a grain boundary, related to the grain boundary energy. Properties of polycrystalline materials are strongly influenced by the network of their internal interfaces. This is because the properties of grain boundaries differ significantly from those of the ideal crystal lattice. For example, incompatible elements can be stored (segregated) on the grain boundary planes and element diffusion is orders of magnitude faster along grain boundaries than through the crystal lattice.Various studies show that the GBCD changes with chemistry of the grain boundaries and modifications are readily observed at concentrations below one wt.%. These chemical impurities also influence the grain boundary energy, grain boundary mobility and its strengths.Preliminary measurements on olivine aggregates also show a chemical dependence of the GBCD. Based on these promising preliminary results, I propose to investigate the effect of chemical variation (including the presence of melt) on the GBCD of olivine. Such data are urgently needed to quantify grain boundary controlled processes in olivine dominated rocks, they may, for example, explain the large discrepancies in deformation experiments that seem to correlate with the materials purity.With the planned research the following questions will be addressed: (iv) Do grain boundary plane frequencies depend on the chemical environment?a. Do grain boundary frequencies vary with the addition of relatively incompatible elements to the aggregate?b. Do grain boundary frequencies change in the presence of melt?(v) Which are the important grain boundaries to be studied in depth? (vi) Do changes in the GBCD affect the activation of different deformation mechanisms, such as deformation in the diffusional accommodated grain boundary sliding regime?