Twinning structures in near-stoichiometric lithium niobate single crystals

A near-stoichiometric lithium niobate single crystal has been grown by the Czochralski method in a hanging double crucible with a continuous powder supply system. Twins were found at one of the three characteristic growth ridges of the as-grown crystal. The twin structure was observed and analyzed by transmission synchrotron topography. The image shifts Delta X and Delta Y in the transmission synchrotron topograph were calculated for the 3 (2) over bar(1) over bar2 and 0 (2) over bar 22 reflections based on results from high-resolution X-ray diffractometry. It is confirmed that one of the {01 (1) over bar(2) over bar}(m) planes is the composition face of the twin and matrix crystals. The formation mechanism of these twins is discussed.