The Czochralski growth of LiBO2 and Li2B4O7

Large single crystals of LiBO2 and Li2B4O7 containing both natural lithium and isotopically pure 6Li have been grown from the melt using the Czochralski technique. The melt was contained in a nickel crucible under a high purity argon atmosphere. Counter rotation of the melt and seed at 10 rpm and a pulling rate of 2.5 mm h-1 gave the best results. In the case of Li2B4O7 slow cooling of the boule over two days was necessary in order to prevent severe cracking. Even under these conditions some cracking could not be avoided. For LiBO2 a strong growth preference along (010) was observed. Growth rates normal to the preferred direction were also anisotropic, producing unusual wedge-shaped crystals. Li2B4O7 could be grown along (102) with no marked growth preference normal to this direction.