(a) The Aurivillius homologous series of phases, typically written but here denoted as where , consists of alternating pyramidal layers and perovskite slab layers. (b) Layer-to-layer charge disparity can stabilize Aurivillius phases in the absence of bulk thermodynamic stability, in contrast to (c) Ruddlesden–Popper phases, with charge-neutral layers. (Charge labels do not imply structural units of crystallization.)
XRD analysis indicates a phase-pure epitaxial film. (a) scans indicate a 6.44 nm -axis lattice parameter, and (b) a -scan of the peak and (c) an -scan (rocking curve) of the peak indicate high crystalline quality, with FWHMs of 1.0° and 0.03°, respectively.
RBS analysis of a sister film deposited under identical conditions on a (001) substrate, showing a stoichiometric composition and high film quality, with and .
TEM analysis confirms the successful synthesis of phase-pure . (a) Cross-section HRTEM image demonstrating a single-phase film. The horizontal dark bands of contrast correspond to the layers. (b) HRTEM image of a single unit cell and corresponding schematic of the crystal structure. (c) Electron diffraction patterns taken along the three principal crystal axes. (d) Cross-section TEM of the full film thickness shows regular spacing through the film thickness. A low density of OPB defects, many dissociated over several nanometers in the plane, is apparent.
AFM image of the surface of the film, showing growth spirals emanating from dislocations with screw component on the surface with formula-unit steps 3.2 nm in height.
(a) Impedance analysis shows some indications of relaxorlike behavior in-plane (10, 100, and 1000 kHz) and a in this dielectric constant vs temperature plot. (b) vs for phases. Prior data are taken from Refs. 68 and 69. Bulk has no ferroelectric transition down to 0 K.
Charge vs electrical field measurements reveal ferroelectric behavior in-plane appreciably below at 100 K (solid lines) and only slight nonlinearity above (dashed lines), which is still in the transition region due to the broadness of the transition. The inset shows the same data scaled to remove the relatively high linear dielectric contribution to show to the eye a ferroelectric polarization loop with low loss.
Schematics of the IDC modeled for this study. (a) Overview and (b) detail, showing variables and dimensions in microns.
Comparison of the application of the different models for the extraction of permittivity from capacitance data collected at 10 kHz.
Results of calculation of the proportionality factor and the contributions by air and the substrate to the total capacitance measured on the IDC on the films, shown for both reported approaches and for this work.
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