Lattice defects in single-crystal lithium niobate I. Transmission electron microscopy

Abstract

Residual ferroelectric 180° domains in YZ-LiNbO₃ wafers have been studied by transmission electron microscopy. In many cases domain walls lie pinned in the plane of a small-angle grain boundary while the other corresponding domain wall stays at a distance of about 20 μm even against an electric poling field. The diffraction contrast of domain walls and of grain boundary dislocations was investigated. Burgers vectors of 1/3[1101] and 1/3[01Tl1] have been identified by means of computer simulation of their contrast Taking into account the piezoelectric effect does not markedly change the simulated dislocation images but is responsible for inner electric fields around dislocations which determine the interaction of small-angle grain boundaries with ferroelectric domain walls. This might explain why the poling field which is usually applied after crystal growth is in many cases not sufficient to obtain single-domain YZ-LiNbO₃.