Microstructure and Nanoscale Piezoelectric/Ferroelectric Properties in La2Ti2O7 Thin Films Grown on (110)-Oriented Doped Nb:SrTiO3 Substrates

作者：Shao Zhenmian^*; Saitzek Sebastien; Roussel Pascal; Ferri Anthony; Bruyer Emilie; Sayede Adlane; Rguiti Mohamed; Mentre Olivier; Desfeux Rachel

来源：Advanced Engineering Materials, 2011, 13(10): 961-969.

DOI：10.1002/adem.201100105

(00l)-Oriented La2Ti2O7 (LTO) thin films with monoclinic perovskite-layer structure [a = 7.806(2) angstrom, b = 5.552(3) angstrom, c = 13.015(5) angstrom, beta = 98.62(2)degrees] have been grown by a sol-gel route on conducting (110)-oriented doped Nb:SrTiO3 (STO) substrates. The narrow rocking curves (0.24 degrees width for 004(LTO) peak) demonstrate the sharp mosaicity of the films. Using high-resolution X-ray diffraction (HR-XRD), epitaxial relationships between the LTO, and the STO substrate are given. In addition, HR-XRD evidences the existence of (212)-oriented crystallites 1.5 degrees disoriented with respect to the plane of the substrate. We confirm, by DFT calculations, that the polarization vector lies in the b-axis of the LTO cell and consequently, the existence of these (212)-oriented crystallites enables to explain the origin of the various contrasts observed both on the in-plane and out-of-plane images when collected by piezoresponse force microscopy. Finally, both successful poling experiments performed via the tip of atomic force microscope and the existence of local piezoloops within the domains, unambiguously confirm the ferroelectric state of the films at the nanoscale level. Once again, this study demonstrates that a clear understanding of nanoscale piezoelectric/ferroelectric phenomena in oriented thin films passes through a carefully structural analysis as performed by by HR-XRD.

• 出版日期2011-10