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 ΔX and ΔY in the transmission synchrotron topograph were calculated for the 32 and 022 reflections based on results from high-resolution X-ray diffractometry. It is confirmed that one of the {01}_m planes is the composition face of the twin and matrix crystals. The formation mechanism of these twins is discussed.