Film thickness dependence of in-plane ferroelastic domain structure in constrained tetragonal PbTiO3 films induced by isotropic tensile strain

In this study, the ferroelectric phase of PbTiO3 (PTO) thin films was grown on cubic single-crystal KTaO3 (KTO) substrates using metal-organic chemical vapor deposition. X-ray diffraction (XRD) was used to reveal an a(1)/a(2) domain structure, which remained unchanged down to a film thickness of 2 nm. The a(1) and a(2) polydomains do not have a simple tetragonal symmetry because a(a & PAR;) and a(a)(& BOTTOM;) do not have the same values. The crystallographic tilt angle, alpha, is defined based on the rotation angle of the PTO lattice with respect to the cubic phase of KTO substrates. The in-plane tetragonal distortion (c(a| |)/a(a| |)) and alpha decreased with the decrease in the film thickness, following the in-plane tetragonal geometric equation: alpha = tan - 1 ( c (a | | )/ a a| | ) - 45 & DEG;. The isotropic tensile strains induced in-plane polarization directions along the [100] and [010] axes of the substrates. These axes are formed via the a(1)/a(2) polydomain of the tetragonal-like phase. Moreover, synchrotron in-plane grazing incidence XRD and piezoelectric force microscopy were used to reveal the thickness dependency of the periodic domain width of the ferroelastic a(1)/a(2) domain. The periodic domain width in the PTO films decreased, following Kittel's law, with the reduction in the film thickness. Published under an exclusive license by AIP Publishing.