Growth and characterization of large-size bismuth germanate single crystals by low thermal gradient Czochralski method

Nearly perfect Bi4Ge3O12 (BGO) single crystals of similar to 40 mm diameter and similar to 80 mm length were grown along [0 0 1] by low thermal gradie nt Czochralski method employing automatic high-resolution weight control fe ed back loop. Optimized growth parameters were: seed pulling rate 2.5 mm/h and seed rotation rate 38 rpm. High-resolution X-ray diffractometry and top ography methods were used to characterize these crystals by employing a dou ble crystal X-ray diffractometer designed and developed at NPL. Major part of the crystal discs examined were found to have high degree of perfection with diffraction curve half-widths of similar to 9 arcsec. However, small r egions at the peripheries of the discs showed very low angle grain boundari es with tilt angle of similar to 30 arcsec. The subgrains were directly ima ged in high-resolution X-ray diffraction topographs. (C) 1999 Elsevier Scie nce B.V. All rights reserved.