High-resolution electron microscopy of 90° ferroelectric domain boundaries in BaTiO 3 and Pb(Zr 0.52Ti 0.48)O 3

Abstract

90° domain boundaries in BaTiO 3 and PZT(52/48) have been studied with high-resolution electron microscopy. The high-resolution images with two-dimensional 4 Å lattice fringes show that most 90° domain boundaries in BaTiO 3 are parallel to (011) planes but can shift from one (011) plane to adjacent (011) planes. It is suggested that such shifts may occur on (01 1 ) or (001) planes. Across the domain boundary, lattice planes tilt about 0.5° in BaTiO 3, which is close to the experimental value 0.6° from the selected-area diffraction pattern and the theoretical value 0.57°. In PZT(52/48), the tilt of lattice planes across the domain boundary in high-resolution images is only about 1°, which is smaller than the experimental value 2.8° from selected-area diffraction pattern and the value from theoretical calculation. The mismatch may indicate that in very thin films the lattice distortion and strain field can be relaxed. A diffuse dark contrast is found along 90° domain boundaries in both BaTiO 3 and PZT(52/48) and is probably related to the lattice distortion or ionic displacement. The diffuse dark lines are about 4–10 unit cells wide around the domain boundary. Diffractograms from Fourier analysis of the regions in high-resolution images around the domain boundaries reveal the effects of the lattice distortion and strain field.