Thickness-dependent a1/a2 domain evolution in ferroelectric PbTiO3 films

Ferroelectric a1/a2 domain structure has great potentials in high dielectric capacitors and tunable microwave devices. Understanding its structure is crucial to better control the domain configurations for future applications. In this paper, PbTiO3 thin films with variant thicknesses are deposited on (110)-oriented GdScO3 substrates by Pulsed Laser Deposition (PLD) and investigated by using conventional transmission electron microscopy (TEM) and Cs-corrected Scanning TEM. Contrast analysis and electron diffractions reveal that PbTiO3 films are domain oriented consisting of a1/a2 and a/c domain structure. The a1/a2 domains are found to distribute periodically and its width increases with increasing film thickness following square root rule. Cs-corrected STEM imaging demonstrates that the domain walls of a1/a2 domain structure have the rotation characteristic of 90° ferroelastic domain wall. The interchange of a1/a2 domains induces the formation of vertex domains composed of two 90° and one 180° domain walls. Strains are mainly concentrated on the domain walls. The formation of this complex domain configuration is discussed in terms of the effect of the misfit strain, film thickness and cooling rate. These results provide novel information about a1/a2 domain structures and are expected to shed some light on modulating a1/a2 ferroelectric domain patterns in the design of ferroelectric-based devices.

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