GROWTH-RATE DISPERSION - THE ROLE OF LATTICE STRAIN

Several physical models are proposed which relate the mosaic spread found in secondary nuclei to the phenomenon of growth rate dispersion: point defects, (random) distribution of dislocations, grain boundaries and volume strain variations in crystals. Comparison of the theoretical models with available experimental data, indicate that the physically most relevant picture in this case is to assume the presence of low-angle grain boundaries in the secondary nuclei which influence the growth rate of these crystals. The length scale associated with these grain boundaries is of the order of 0.5-1.0-mu-m and can be quantitatively understood from the length scale involved in abrasion processes. The growth rate expression not only comprises the "overall" lattice strain, but also the size of the crystal which implies a size-dependent growth rate, a term frequently encountered in industrial crystallization, but still not well described.