Ferroelastic domain structure and switching in epitaxial ferroelectric thin films

Unique ferroelastic polytwin domains are formed in epitaxial ferroelectric thin films prepared on single-crystal substrates and critically influence various ferroelectric properties. This chapter reviews theoretical as well as experimental studies on various thermomechanical strain factors and their relaxation involved in domain formation and switching during film processing and device fabrication and application. Two major strain relaxation mechanisms, misfit strain relaxation by dislocations and the formation of polytwin structures, are reviewed. The critical factors controlling the final domain structures, such as substrate selection, film composition, film thickness, introduction of an interlayer, and the lateral size of film patterning, are described in detail. This chapter also includes recent experimental evidence of ferroelastic domain switching in such highly confined epitaxial thin films as well as in small islands.