Chemical twinning and ferroelectric domains in LiTaO₃

Abstract

Ferroelectric twinning, with {0112} and {0114} twin composition planes, has been induced in lithium tantalate by partial exchange of Li⁺ by Ag⁺. This process leads to new types of ferroelectric domains, which involve rotations of the polarization vector by 66°, 104°, 75.4° and 104.6°. The domain walls are chemical in origin and very much more stable than the well-known 180°-ferroelectric domains in pure LiTaO₃. The structure of the domain walls is clarified by a crystallographic analysis of the possible structures and interpretation of high-resolution electron microscope images and selected-area diffraction patterns. Non-polar boundaries, or stacking faults, and recurrent twin dislocations, or ‘swinging superlattice structures’, were also observed and analysed.