High-quality epitaxial five-layer Aurivillius films with in-plane ferroelectricity for electrocaloric cooling [Dataset]

High-quality purely c-axis oriented epitaxial thin films of the Aurivillius phase Sr2Bi4Ti5O18 with n = 5 (Sr,Bi)TiO3 perovskite-like layers, are grown on SrTiO3 substrates by pulsed laser deposition. The highest crystalline quality is obtained with a 20 wt.% Bi-excess target and average stacking order values in the proximity of the ideal value n = 5 are attained for an optimum deposition temperature of 650 °C. Scanning transmission electron microscopy reveals regions with n ranging from 4 to 6 around an average thickness of n = 5, in agreement with the X-ray diffraction analysis. Interdigital electrodes are used to probe the in-plane polarization and survey the electrocaloric properties. A maximum adiabatic temperature change of ΔT ∼ 0.95 °C for an electric field of 150 kV cm−1 is observed at ≈135 °C. Larger values are expected at higher temperatures around the ferroelectric Curie temperature, TC. Since TC of Sr2Bi4Ti5O18 can be tuned by codoping, the findings pave the way toward a large electrocaloric effect at ambient temperature.

[Description of methods used for collection/generation of data]: The structural characterization of the films was performed by X-ray diffraction (XRD) 2θ/ω wide scans, X-ray reflectivity (XRR) and reciprocal space maps (RSMs) of selected asymmetric reflections, by using a four-circle X-ray diffractometer (Malvern-Panalytical X'pert Pro MRD) and standard Cu Kα1,2 X-ray source with a parabolic mirror (for reciprocal space maps, a 2xGe(220) monochromator was added to the incident optics). A 2D array PIXcel detector was used. The topography of selected films was studied using atomic force microscopy (AFM) in contact mode (Keysight 5100) over different areas. The structure of the films was also analyzed by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) on a Fisher Spectra microscope operated at 200 kV. Cross-section lamellas were prepared by focused ion beam (FIB) on a SBTO5 film deposited under optimized conditions, with the cut oriented to show STO [100] zone axis.