Distribution of OH in synthetic and natural quartz crystals

Abstract

The relative intensities of different OH vibration bands have been studied in synthetic quartz crystals with total OH concentration varying by more than a factor of 30 by means of infrared absorption measurements at 78°K. Local variations of OH concentration also have been measured for different directions in these samples and in two crystals of natural quartz from Brazil. Integral absorptions of the different bands in the 3400 cm −1 region were all found to increase linearly with total OH concentration. Therefore, mechanical Q could be related to any one band of the spectrum as well as to the total OH concentration. Since for natural quartz no relation between total OH concentration and mechanical Q seems to exist, the effect of OH defects characteristic for synthetic quartz must be high, while the OH defects characteristic for natural quartz (i.e., rock crystals and smoky quartz) have a small effect on the mechanical Q. OH concentrations in the Z- and + X-zones were found to be lower near the edge than near the seed. The concentration of OH varies in the order Z < + X ⪡ − X, suggesting that OH acts as a charge compensator for metal impurities, notably Al +3. In natural quartz, the OH concentrations near the edge were also lower than in the interior parts. The overall differences for different directions were much smaller than in the case of synthetic quartz.