X-ray diffraction of ferroelectric nanodomains in PbTiO₃ thin films

X-ray diffraction constitutes a powerful technique with which to characterise ferroelectric domains. Here we describe the principles of ferroelectric nanodomain diffraction and present some results for PbTiO ₃ thin films grown under tensile strain on two different substrates, with, thicknesses below and above the critical thickness for strain relaxation. The combination of conventional and grazing incidence diffraction and the analysis of the scattering between Bragg peaks allowed the identification of a new polar symmetry in ultra-thin films with only anti-parallel 18° domains. Thick films showed tetragonal 90° ferroelectric/ferroelastic domains instead, with a depressed TC and a domain periodicity largely independent of temperature.