Open AccessUnderstanding Strain‐Induced Phase Transformations in BiFeO 3 Thin Films
Author(s) -
Dixit Hemant,
Beekman Christianne,
Schlepütz Christian M.,
Siemons Wolter,
Yang Yongsoo,
Senabulya Nancy,
Clarke Roy,
Chi Miaofang,
Christen Hans M.,
Cooper Valentino R.
Publication year - 2015
Publication title -
advanced science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.388
H-Index - 100
ISSN - 2198-3844
DOI - 10.1002/advs.201500041
Subject(s) - materials science , phase (matter) , tetragonal crystal system , piezoelectricity , band gap , thin film , condensed matter physics , epitaxy , octahedron , blueshift , strain (injury) , elastic energy , phase transition , crystallography , strain engineering , strain energy , nanotechnology , chemical physics , optoelectronics , composite material , chemistry , crystal structure , thermodynamics , physics , photoluminescence , medicine , organic chemistry , layer (electronics) , finite element method
Experiments demonstrate that under large epitaxial strain a coexisting striped phase emerges in BiFeO 3 thin films, which comprises a tetragonal‐like ( T ′) and an intermediate S ′ polymorph. It exhibits a relatively large piezoelectric response when switching between the coexisting phase and a uniform T ′ phase. This strain‐induced phase transformation is investigated through a synergistic combination of first‐principles theory and experiments. The results show that the S ′ phase is energetically very close to the T ′ phase, but is structurally similar to the bulk rhombohedral ( R ) phase. By fully characterizing the intermediate S ′ polymorph, it is demonstrated that the flat energy landscape resulting in the absence of an energy barrier between the T ′ and S ′ phases fosters the above‐mentioned reversible phase transformation. This ability to readily transform between the S ′ and T ′ polymorphs, which have very different octahedral rotation patterns and c / a ratios, is crucial to the enhanced piezoelectricity in strained BiFeO 3 films. Additionally, a blueshift in the band gap when moving from R to S ′ to T ′ is observed. These results emphasize the importance of strain engineering for tuning electromechanical responses or, creating unique energy harvesting photonic structures, in oxide thin film architectures.