Sweeping and irradiation effects on hydroxyl defects in crystalline natural quartz.
A study of electrodiffusion (sweeping) and irradiation effects on hydroxyl defects has been carried out on good quality optically clear natural quartz crystals. The crystals were of Arkansas and Brazilian origin which are used as starting material in hydrothermal synthesis of high purity cultured quartz crystals. In particular, various OH(- ) related point defects have been monitored using infrared absorption measurements in the 3100-3700 cm(-1) range. Our estimates from sweeping and irradiation results show that the Brazilian crystal had a much higher concentration of hydrogen than the Arkansas crystal. We have therefore designated the Brazilian crystal as "high-H" and Arkansas stone as "low-H" quartz. High- and low-H samples of natural quartz in three different conditions, unswept, Na-swept, and H-swept, were subjected to a sequence of low- and room-temperature irradiations that separate proton and alkali motion. Irradiation at 77 K reduces the strength of almost all the IR bands except the short-bond Al-OH(-) center. Warm up to room temperature results in significant recovery (85-95%). Al-OH(-) centers in natural quartz were found to exhibit irradiation characteristics similar to those of cultured quartz. For similar radiation doses (2 Mrad) the prominent bands, Li and H dependent at 3476 cm(-1) (designated as Li-n3a) and Na and H dependent at 3451 cm (-1) (designated as Na-n2a) showed a larger decay at 300 K-irradiation than at 77 K. The prominent H-dependent OH(-) band at 3468 cm(-1) (designated as H-n2a) did not show any depletion of peaks after 300 K-irradiation while the 77 K-irradiation reduced their strength to about 10% of the as-H-swept strength. The results have been discussed in terms of protons and alkali ions motion to shallow and deep traps and compared with cultured quartz.
Bahadur
H
H
Nat. Phys. Lab., New Delhi.