Effect of crystal composition on the domain structure of LiNbO₃ grown from Li-rich melts by the Czochralski technique

Crystals of LiNbO₃ have been grown by the Czochralski technique from off-stoichiometric melts containing excess Li₂O (54.5, 58 and 63 mol%). The spacial compositional analysis of the crystals along the growth direction has been carried out using the optical absorption technique. The compositional gradient becomes severe as the Li₂O concentration in the initial growth melt increases. The domain structure in the crystals grown from unpoled seeds exhibit a mono-domain nature for the melt containing 58% Li₂O. Nevertheless, both at lower and higher levels of Li₂O, the crystals always grow in poly-domain form. Interestingly, for the crystals grown from 58% Li₂O, the initial unpoled seed also gets poled during the growth. A domain inversion region at the seed crystal boundary is observed. A correlation between the crystal composition and domain structure has been observed. Perfectly stoichiometric crystals exhibit single domain nature.