Control of defect concentrations in single crystals: Insights from micro-IR on natural quartz crystals

摘要

The physical properties of single crystals are highly dependent on trace impurities contained within them. For synthesis of single crystals with prescribed properties, precise and accurate control of impurity content can be extremely desirable. We review and expand on studies of crystals from the natural environment that document systematic order-of-magnitude variations in defect abundances. Using high-resolution FTIR, we demonstrate that the dominant control on the uptake of defects in growing quartz crystals is the growth rate of the advancing crystal face. We show that the uptake of different kinds of defects have the same functional dependence both on crystal growth rate and on the crystallographic orientation of the growth face. In unaltered quartz crystals, concentrations of LiOH, HOH species (which reside in voids), and Al-bearing species (which substitute for Si within the crystal structure) are proportional to one another despite fast and slow growth on both 'r' and 'z' rhombohedral growth faces. In addition, our measurements can distinguish the effects of processes, such as internal diffusion and fluid exchange, which have re-set the abundances of defect species after crystal growth; A1OH, HOH, and LiOH show increasing propensities for secondary mobility and are dependent on the crystallographic orientation of the original growth face which incorporated them.