Formation mechanism of twin boundaries in lithium tetraborate

We investigated the relationship between crystal growth direction and twin boundary orientation in lithium tetraborate. We found that there are two twin boundary orientations, {1 0 0} and {1 1 2}, and that the twin boundary orientation depends on the growth interface orientation. Using the micro-pulling-down method, the tilting angle of a seed crystal containing a (0 1 0) twin boundary has a critical effect on controlling the twin boundary orientation. Only a (0 1 0) twin boundary forms in a growing crystal for tilting angles between 0° and 45°, whereas both (0 1 0) and (1 0 0) twin boundaries form when the tilting angle is 45°. Employing a periodic twin structure in a borate crystal may be useful for fabricating quasi-phase-matching structures since the twin boundary orientation could be controlled by selecting an appropriate growth direction.

► We investigated the relationship between crystal growth direction and twin boundary orientation in lithium tetraborate. ► We found that there are two twin boundary orientations, {1 0 0} and {1 1 2}, and that the twin boundary orientation depends on the growth interface orientation. ► When both (1 0 0) and (0 1 0) twin boundaries are formed at the 〈1 1 0〉 growth, the gap between (1 0 0) and (0 1 0) twin boundaries expands with growth. A (1 1 2) twin boundary forms in this gap because it is parallel to the facet plane.