posted on 2020-03-11, 15:45authored byV. Demange, Q. Simon, F. Gouttefangeas, L. Joanny, M. Guilloux-Viry
Tetragonal
tungsten bronze (TTB) phases possess numerous important
properties (ferroelectricity, multiferroicity, piezoelectricity, optical
nonlinearity, electro-optics) that can be achieved by modifying their
composition, in addition to their ability to grow as very anisotropic
crystals. In this study, K5.06(Ta0.57Nb0.43)10.99O30 tetragonal tungsten bronze
phase thin films were grown by a pulsed laser deposition technique
on (001)SrTiO3 and R-plane sapphire substrates. The films
grew according to two modes with respect to the substrate surface,
that is, as vertical nanorods with the [001] direction perpendicular
to the substrate surface and as horizontal nanorods with the [001]
orientation parallel to the substrate surface and ⟨310⟩
out-of-plane direction. Both vertical and horizontal nanorods present
epitaxial relationships with the substrates. Careful study of epitaxial
relationships showed a complex growth on both substrates that can
be described in the framework of domain matching epitaxy resulting
in several antiphase domain formations for both kinds of nanorods.
These particular configurations are due to a high degree of coincidence
between cations (anions) of the film with those of the substrate.
This study shows the ability of ferroelectric TTB phases to grow as
one-dimensional objects with the possibility to tailor their polarization
direction either normal to or parallel to the substrate surface.