Perfektion von CaF2-einkristallen in abhängigkeit von der zuchttechnik

Abstract

To investigate the dependence of crystal perfection on growth conditions, a number of calcium fluoride crystals were grown with different growth techniques and growth parameters. The crystals were examined for stress induced birefringence with the polarizing microscope, for dislocations with chemical etches and for anion vacancies with X-irradiation. The following growth techniques were used: (1) Growth from the melt by the (a) Bridgman- and (b) Czochralski-methods, (2) growth by sublimation, (3) flux growth (CaCl2/NaF), and (4) gel growth (starch). These techniques involve both different growth temperatures (melt growth 1405°C, vapour phase growth ca. 1405°C flux growth ca. 1000°C, gel growth ca. 20 c) and different growth rates (melt growth ca. 1–10 mm/h, vapour phase growth ca. 1 mm/h, flux growth ca. 0.1 mm/h, gel growth ca. 10−4 mm/h). The melt grown and vapour phase grown crystals had sizes of some cm, the flux grown and gel grown crystals of about 1 mm. The crystals were etched with 3 M HCl and X-rayed by copper radiation. Dependent on the growth techniques and different growth parameters the dislocation densities varied from 102 (vapour phase grown crystals) up to 106 cm−2 (Czochralski grown crystals), the anion vacancies from 1017 (vapour phase grown crystals) up to 1019 cm−3 (Czochralski grown crystals).