Formation of needle-shaped domains in a surface layer of X-cut lithium niobate

The formation of needle-shaped domains in a surface layer of X-cut lithium niobate in the electric field of contact electrodes is studied. It is found that a voltage of 1200–1250 V produces stable needle-shaped domains in an interelectrode gap 140 $\pm$ 5 $\mu$m wide. The domains are from 20 to 30 $\mu$m long and are aligned with the polar axis of the crystal and with electric lines of force. When a voltage of 1300–1350 V is applied to the crystal, the size of the domains increases stepwise and their growth rate rises considerably to about 1 $\mu$m/s. The domains localize within 300–600 $\mu$m from the edge of the electrodes because of the increase in the electric field strength at right angles. The sizes of the domains differ greatly because of microscopic defects present at the electrode boundaries.