Abstract
This work is aimed at studying asymmetric ((BT) (1 − x)Λ/(BZ) xΛ) superlattices, grown by pulsed laser deposition onto (001) MgO substrates. The thicknesses of BT (ferroelectric) and BZ (paraelectric) layers were varied so that х ranged from 0 to 1 at a modulation period Λ of about 80 Å. The films were 400 nm thick. The out‐of‐plane lattice parameters of constituents were assessed using X‐ray diffraction. The lattice dynamic peculiarities of superlattices were probed via Raman spectroscopy; special attention is paid to the analysis of E(1TO) and A1(2TO) ferroelectric soft modes. A comparative analysis of data acquired via both experimental techniques reveals the enhancement of stress between BT and BZ layers with a decrease in symmetry from the tetragonal to a monoclinic phase due to strains induced by the lattice parameter mismatch between the constituents.
Highlights
Over the last 50 years, materials based on ferroelectric perovskites, such as artificial superlattices, have attracted attention of researchers due to their outstanding properties, such as high dielectric constants, high polarization, low dielectric losses, and high Curie temperature, which find application in various optoelectronic and microelectronic devices: nonvolatile random access memory devices, integrated systems, and tunable microwave elements [1,2,3,4,5,6,7,8,9,10]
In contradistinction to single-composition ferroelectric thin films, artificial superlattices (SLs) ensure high permittivity and great polarization in the relevant systems [3, 9]. e structures, where one constituent is ferroelectric BaTiO3 (CT) and another is dielectric SrTiO3 (ST) or PbTiO3 (PT) or paraelectric BaZrO3 (BZ), are among the most extensively studied objects. is is due to the fact that their physical characteristics are determined by epitaxial strain that is caused by the lattice parameter mismatch between constituents
Strains induced by the lattice parameter mismatch of the adjacent layers alter the ion positions and lattice vibrations, especially in low-frequency ferroelectric soft modes (E(1TO)) that are highly sensitive to ion displacements in thin films. us, the soft modes may furnish detailed information on misfit strains and, on the phase transitions in ferroelectric superlattices, which is essential in terms of the fundamental science and the practical use of these structures
Summary
Over the last 50 years, materials based on ferroelectric perovskites, such as artificial superlattices, have attracted attention of researchers due to their outstanding properties, such as high dielectric constants, high polarization, low dielectric losses, and high Curie temperature, which find application in various optoelectronic and microelectronic devices: nonvolatile random access memory devices, integrated systems, and tunable microwave elements [1,2,3,4,5,6,7,8,9,10]. X-ray diffraction is known to be one of the most reliable methods for studying epitaxial strain in superlattices [16,17,18], because it ensures information on the degree of structural perfection of films and allows one to determine the lattice parameters and to establish the orientation between the film and the substrate. Raman spectroscopy is a nondestructive and powerful method for lattice dynamics characterization in perovskites [2, 4, 9, 14, 15, 19] and allows one to detect even the finest atomic displacement in a system under consideration by tracking transformations in ferroelectric soft modes that are the main indicators of misfit strain in such systems
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
