The present investigation deals with the effect of the change in the m
elt depth in the crucible (during pulling) on the temperature distribu
tion in the melt and on the critical crystal rotation rate, and hence
on the growth of Bi12SiO20, Bi12GeO20, Bi4Si3O12 and TeO2 oxide crysta
ls. The need to terminate the growth before a critical value of the me
lt depth is reached and the difficulty in getting good quality crystal
s beyond this point is reported.