THE GROWTH AND CHARACTERIZATION OF BI4TI3O12 SINGLE-CRYSTALS USING A FLOATING-ZONE METHOD

Single-crystal rods and fibres of Bi4Ti3O12 of various sizes oriented along [100] direction were successfully produced by a floating-zone me thod. Each of these crystals has a purely orthorhombic structure and a clear Curie transition at 668.8 degrees C (with a peak at 675.9 degre es C). Investigation of the growth characteristics revealed that the v aporization of Bi2O3 is dependent on the quality of the source rod, th e growth rate and the length of the molten zone. For a source rod of p ure Bi4Ti3O12, a growth rate of 30-35 mm h(-1) and a sufficiently shor t molten zone (for example 1.7-2.0 mm for growth of a 2.8-3.2 mm diame ter crystal), a good (transparent, without cracks or inclusions) Bi4Ti 3O12 single crystal can be produced directly from the stoichiometric s ource rod. Otherwise, a source rod with excess Bi2O3 is necessary to c ompensate for the vaporization of Bi2O3 during the growth process. The excess amount of Bi2O3 required is dependent on the sintered state of the source rod, the growth rate and the phase structures of the origi nal powders from which the source rod had been pressed. In general, an increase in growth rate or in sintering temperature can decrease the required excess amount of Bi2O3 in the source rod. However, the excess amount of Bi2O3 required can be dramatically decreased by making the source rod from Bi12TiO20 and TiO2.