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

Epitaxial ${\mathrm{SrBi}}_2{\mathrm{Ta}}_2{\mathrm{O}}_9$ (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 ${\mathrm{SrTiO}}_3$ substrates. X-ray diffraction pole figure and $\mathrm{\phi -}\mathrm{scan}$ measurements revealed that the three-dimensional epitaxial orientation relation $\mathrm{SBT}\text{(001)‖}{\mathrm{SrTiO}}_3\text{(001),}$ and $\mathrm{SBT}\text{[11̄0]‖}{\mathrm{SrTiO}}_3\text{[100]}$ is valid for all cases of SBT thin films on ${\mathrm{SrTiO}}_3$ 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 $\text{(∼0.6}$ nm). The grains of (103)-oriented SBT films were arranged in a triple-domain configuration consistent with the symmetry of the ${\mathrm{SrTiO}}_3\text{(111)}$ substrate. The measured remanent polarization ${\text{(2P}}_r)$ and coercive field ${\text{(2E}}_c)$ of (116)-oriented SBT films were 9.6 $\mu {\mathrm{C/cm}}^2$ and 168 kV/cm, respectively, for a maximum applied electric field of 320 kV/cm. Higher remanent polarization ${\text{(2P}}_r\text{=10.4}$ $\mu {\mathrm{C/cm}}^2)$ and lower coercive field ${\text{(2E}}_c\text{=104}$ 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.