Growth crystallography of Bi12SiO20 single crystals solidified by a floating zone method

Relations between the growth directions of Bi12SiO20 (BSO) single-crystal rods solidified by a floating zone method and the pulling parameters 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 direction of the produced BSO single-crystal rod is related to the pulling rate. Statistically, the probability of the growth direction approaching 〈0 1 1〉, 〈1 1 2〉 or 〈0 0 1〉 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 orientation 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 appears to incline mostly to 〈1 1 2〉 if the seed orientation is near 〈0 1 1〉 or 〈1 1 1〉 but far from 〈0 0 1〉, or to 〈0 0 1〉 if the seed orientation is near 〈0 0 1〉 but far from both 〈0 1 1〉 and 〈1 1 1〉. The angle of inclination increases with the pulling rate, and also with the difference in angle between the orientation of seed crystal and 〈1 1 2〉 or 〈0 0 1〉. The facet morphology of the BSO single-crystal rod is related to its growth direction. The cross-section of the BSO single-crystal rod grown along 〈0 0 1〉 is an octagon with tetrad-rotational symmetry, that grown along 〈0 1 1〉 is an ellipsoid with diad-rotational symmetry, and that along 〈1 1 1〉 is a hexagon with triad-rotational symmetry. The cross-sections of the BSO single-crystal rods grown in other directions are not regular, because there is no clear symmetry.