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Title: Understanding strain-induced phase transformations in BiFeO3 thin films

Experiments demonstrate that under large epitaxial strain a coexisting striped phase emerges in BiFeO₃ 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 BiFeO3 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.
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [6] ;  [7] ;  [7] ;  [1]
  1. Oak Ridge National Lab., Oak Ridge, TN (United States)
  2. Oak Ridge National Lab., Oak Ridge, TN (United States); Florida State Univ., Tallahassee, FL (United States); National High Magnetic Field Lab., Tallahassee, FL (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Oak Ridge National Lab., Oak Ridge, TN (United States); ASML, Veldhoven (The Netherlands)
  5. Univ. of Michigan, Ann Arbor, MI (United States); Univ. of California, Los Angeles, CA (United States)
  6. Univ. of Michigan, Ann Arbor, MI (United States)
  7. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Publication Date:
OSTI Identifier:
Grant/Contract Number:
AC02-05CH11231; FG02-06ER46273; AC02-06CH11357
Accepted Manuscript
Journal Name:
Advanced Science
Additional Journal Information:
Journal Name: Advanced Science; Journal ID: ISSN 2198-3844
Research Org:
Argonne National Laboratory (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
36 MATERIALS SCIENCE multiferroic BiFeO₃; phase coexistence; piezoelectric response; solid-state nudged elastic band method