Growth of nearly perfect alkali halide single crystals by Czochralski method and their characterisation

Abstract

Nearly perfect single crystals of KCl with diameters in the following ranges were grown on a crystal puller developed in our laboratory: (i) about 10 mm, (ii) 20–25 mm, (iii) 35–40 mm and (iv) 45–55 mm. The rates of pulling were in the range 10 to 20 mm/h, depending upon the diameter. The maximum length of the crystals was about 100 mm. Carefully selected seeds held in air cooled silver plated copper seed holders were used. The rate of rotation was 30 RPM. The temperature of the melt was controlled manually and could be maintained within ±1°C of the desired value. Conditions for growth of nearly perfect KBr crystals of the following diameters were optimised: (i) about 10 mm, (ii) about 20 mm and (iii) about 40 mm. The rates of growth for these crystals were the same as those for the KCl crystals. These crystals were characterised regarding perfection by transmission X-ray diffraction topography and multi-crystal diffractometry (rocking curves). Edge type dislocations having their line vectors along 〈010〉 and 〈210〉 were observed. The half width of the rocking curves of the present crystals was in the range 10–30 s of arc.