Structural and electrical anisotropy of (001)-, (116)-, and (103)-oriented epitaxial SrBi₂Ta₂O₉ thin films on SrTiO₃ substrates grown by pulsed laser deposition

Epitaxial SrBi₂Ta₂O₉ (SBT) thin films with well-defined (001), (116), and (103) orientations have been grown by pulsed laser deposition on (001)-, (011)-, and (111)-oriented Nb-doped SrTiO₃ substrates. X-ray diffraction pole figure and φ-scan measurements revealed that the three-dimensional epitaxial orientation relation SBT(001)∥SrTiO₃(001), and SBT[110]∥SrTiO₃[100] is valid for all cases of SBT thin films on SrTiO₃ substrates, irrespective of their orientations. Atomic force microscopy images of the c-axis-oriented SBT revealed polyhedron-shaped grains showing spiral growth around screw dislocations. The terrace steps of the c-axis-oriented SBT films were integral multiples of a quarter of the lattice parameter c of SBT (∼0.6 nm). The grains of (103)-oriented SBT films were arranged in a triple-domain configuration consistent with the symmetry of the SrTiO₃(111) substrate. The measured remanent polarization (2P_r) and coercive field (2E_c) of (116)-oriented SBT films were 9.6 μC/cm² and 168 kV/cm, respectively, for a maximum applied electric field of 320 kV/cm. Higher remanent polarization (2P_r=10.4 μC/cm²) and lower coercive field (2E_c=104 kV/cm) than those of SBT(116) films were observed in (103)-oriented SBT thin films, and (001)-oriented SBT revealed no ferroelectricity along the [001] axis. The dielectric constants of (001)-, (116)-, and (103)-oriented SBT were 133, 155, and 189, respectively.