Structure and piezo-ferroelectricity relationship study of (K0.5Na0.5)0.985La0.005NbO3 epitaxial films deposited on SrTiO3 by sputtering

H´Linh H´Mŏk,J M Siqueiros-Beltrones,E Martínez-Aguilar,J J Gervacio-Arciniega,O Raymond-Herrera,X Vendrell

doi:10.1038/s41598-017-17767-3

Abstract

This work demonstrates that the rf-sputtering technique, combined with appropriate heat treatments, is potentially effective to develop new materials and devices based on oxide-interface and strain engineering. We report a study of the structural-physical properties relationship of high crystalline quality, highly oriented and epitaxial thin films of the lead-free (K0.5Na0.5)0.985La0.005NbO3 (KNNLa) compound which were successfully deposited on Nb-doped SrTiO3 substrates, with orientations [100] (NSTO100) and [110] (NSTO110). The crystalline growth and the local ferroelectric and piezoelectric properties were evaluated by piezoresponse force microscopy combined with transmission electron microscopy and texture analysis by X-ray diffraction. Conditioned by the STO surface parameters, in the KNNLa films on NSTO100 coexist a commensurate [001]-tetragonal phase and two incommensurate [010]-monoclinic phases; while on NSTO110 the KNNLa films grew only in an incommensurate [101]-monoclinic phase. Both samples show excellent out-of-plane polarization switching patterns consistent with 180° domains walls; while for KNNLa/NSTO100 ferroelectric domains grow with the polarization pointing down, for KNNLa/NSTO110 they prefer to grow with the polarization pointing up. Comparing with previous reports on epitaxial KNN films, we find our samples to be of very high quality regarding their crystalline growth with highly ordered ferroelectric domains arrangements and, consequently, great potential for domain engineering.

Highlights

In the last decade, lead-free piezoelectric compounds have received considerable attention as potential substitutes of toxic lead-based piezoelectric materials such as lead zirconate titanate (PZT). (KxNa1−x)NbO3 (KNN), belonging to the ABO3 perovskite family, is a promising candidate owing to its high Curie temperature (TC around 400 °C) and excellent piezoelectric properties1–5
In part A of this section, a combination of X-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscope (AFM) techniques and structural simulation are used to investigate the crystalline quality of the epitaxial KNNLa thin films grown on both NSTO substrates (NSTO100 and NSTO110) in regards to the crystalline phases, preferential growth orientations, and epitaxial matching; whereas the in-plane lattice parameters are determined by crystallography texture analysis
In part B, the ferroelectric and piezoelectric behavior of the highly ordered ferroelectric domains arrangements are studied by piezoresponse force microscopy (PFM) analysis focusing on the structural characteristics

Summary

Results and Discussion

In part A of this section, a combination of XRD, TEM, and AFM techniques and structural simulation are used to investigate the crystalline quality of the epitaxial KNNLa thin films grown on both NSTO substrates (NSTO100 and NSTO110) in regards to the crystalline phases, preferential growth orientations, and epitaxial matching; whereas the in-plane lattice parameters are determined by crystallography texture analysis. The interplanar spacing for 2θ = 70.20°, corresponding to crystalline planes of the KNNLa film parallel to the surface is d1 = 1.3396 Å The Φ-scans in Fig. 1d confirm the strong in-plane preferential orientation induced by the STO substrate and the high quality of the epitaxial growth of the KNNLa thin film

Monoclinic Tetragonal

Conclusions

Author Contributions

Additional Information