Growth and characterization of epitaxial ferroelectric lanthanum-substituted bismuth titanate nanostructures with three different orientations

Well-ordered large-area arrays of ferroelectric La-substituted Bi₄Ti₃O₁₂ (BLT) nanostructures were prepared by pulsed laser deposition using gold nanotube membranes as shadow masks. By x-ray diffraction and transmission electron microscopy, it was found that well-defined (001)-, (118)/(100)-, and (104)-oriented BLT nanostructures were obtained on (001)-, (011)-, and (111)-oriented SrTiO₃ single crystal substrates covered with epitaxial SrRuO₃ electrode layers, respectively, through ex situ crystallization at 700 °C. Atomic force microscopy analyses revealed that the epitaxial BLT nanostructures maintain a height of about 100 nm and a lateral size of about 150 nm in spite of the postannealing process. The anisotropic ferroelectric properties of the BLT nanostructures of three different orientations were investigated by scanning force microscopy in piezoresponse mode. The highest effective remanent piezoresponse coefficient (2d_zz) of about 38.0 pm/V was observed in (118)/(100)-oriented BLT nanostructures, whereas (001)- and (104)-oriented nanostructures showed smaller 2d_zz values of 5.0 pm/V and 1.4 pm/V, respectively.