GROWTH CRYSTALLOGRAPHY OF BI12SIO20 SINGLE-CRYSTALS SOLIDIFIED BY A FLOATING-ZONE METHOD

Relations between the growth directions of Bi12SiO20 (BSO) single-crys tal rods solidified by a floating zone method and the pulling paramete rs were studied using an X-ray back-reflection Laue technique. It was found that when a platinum wire is used as a seed, the growth directio n of the produced BSO single-crystal rod is related to the pulling rat e. Statistically, the probability of the growth direction approaching [011], [112] or [001] appears to increase in this order with increase of the pulling rate. In addition when a BSO crystal is used as a seed, the growth direction of the produced BSO crystal rod has the same ori entation as the seed crystal if the pulling rate is less than 30 mm h( -1). If the pulling rate is higher than 30 mm h(-1), the growth appear s to incline mostly to [112] if the seed orientation is near [011] or [111] but far from [001], or to [001] if the seed orientation is near [001] but far from both [011] and [111]. The angle of inclination incr eases with the pulling rate, and also with the difference in angle bet ween the orientation of seed crystal and [112] or [001]. The facet mor phology of the BSO single-crystal rod is related to its growth directi on. The cross-section of the BSO single-crystal rod grown along [001] is an octagon with tetrad-rotational symmetry, that grown along [001] is an ellipsoid with diad-rotational symmetry, and that along [111] is a hexagon with triad-rotational symmetry. The cross-sections of the B SO single-crystal rods grown in other directions are not regular, beca use there is no clear symmetry.