Evaporation induced diameter control in fiber crystal growth by micro‐pulling‐down technique: Bi 4 Ge 3 O 12

Diameter self‐control was established in Bi 4 Ge 3 O 12 fiber crystal growth by micro‐pulling‐down technique. In accordance with Bi 2 O 3 ‐GeO 2 phase diagram, the diameter was controlled due to compensation of solidification with evaporation of volatile Bi 2 O 3 self‐flux charged into the crucible with excess. The crucibles had capillary channels of 310 or 650 μm in outer diameter. The crystals up to 400 mm long and 50‐300 μm in diameter were grown at pulling‐down rates of 0.04‐1.00 mm/min. The melt composition and the pulling rate were generally only two parameters determining solidification rate. As a result, crystals with uniform (± 10%) diameter and aspect ratio up to 10 4 were produced without automation of the process. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)