Twinning in czochralski-grown 36°-RY LiTaO₃ single crystals

The origin of twinning during the Czochralski (CZ) growth of 36°-RY lithium tantalate (LiTaO₃) single crystals is examined, and it is shown that lineages composed of dislocation arrays act as an initiation site for twinning. Two types of lineages expand roughly along three different {1210} planes and two different {1100} planes. The former lineages and some latter lineages are composed of two types of mixed-dislocations with different Burgers vectors, while the other lineages are composed of only one type of edge-dislocation. All the dislocations have the Burgers vector of 〈1210〉 type with the compression side at the +Z side. Twin lamellae on {1012} are generated at a lineage during the CZ growth. We have hypothesized that dislocations in the lineage with b = 1/3〈1210〉 change their extension direction along a slip plane of {1012}, and they dissociate into pairs of partial dislocations with b = 1/6〈2201〉and 1/6〈0221〉 forming twin lamellae on {1012}.