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Title: Structural refinement of Pbnm-type perovskite films from analysis of half-order diffraction peaks

Engineering structural modifications of epitaxial perovskite thin films is an effective route to induce new functionalities or enhance existing properties due to the close relation of the electronic ground state to the local bonding environment. As such, there is a necessity to systematically refine and precisely quantify these structural displacements, particularly those of the oxygen octahedra, which is a challenge due to the weak scattering factor of oxygen and the small diffraction volume of thin films. In this paper, we present an optimized algorithm to refine the octahedral rotation angles using specific unit-cell-doubling half-order diffraction peaks for the a -a -c + Pbnm structure. The oxygen and A-site positions can be obtained by minimizing the squared-error between calculated and experimentally determined peak intensities using the (1/2 1/2 3/2) and (1/2 1/2 5/2) reflections to determine the rotation angle α about in-plane axes and the (1/2 5/2 1), (1/2 3/2 1), and (1/2 3/2 2) reflections to determine the rotation angle γ about the out-of-plane axis, whereas the convoluting A-site displacements associated with the octahedral rotation pattern can be determined using (1 1 1/2) and (1/2 1/2 1/2) reflections to independently determine A-site positions. The validity of the approach is confirmedmore » by applying the refinement procedure to determine the A-site and oxygen displacements in a NdGaO 3 single crystal. Finally, the ability to refine both the oxygen and A-site displacements relative to the undistorted perovskite structure enables a deeper understanding of how structural modifications alter functionality properties in epitaxial films exhibiting this commonly occurring crystal structure.« less
Authors:
 [1] ;  [2] ;  [2] ;  [1] ;  [2]
  1. Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering
  2. Drexel Univ., Philadelphia, PA (United States). Dept. of Materials Science and Engineering
Publication Date:
Grant/Contract Number:
SC0012375; AC02-06CH11357; DMR-1151649
Type:
Accepted Manuscript
Journal Name:
Journal of Applied Physics
Additional Journal Information:
Journal Volume: 121; Journal Issue: 4; Journal ID: ISSN 0021-8979
Publisher:
American Institute of Physics (AIP)
Research Org:
Pennsylvania State Univ., University Park, PA (United States); Drexel Univ., Philadelphia, PA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
74 ATOMIC AND MOLECULAR PHYSICS; rotation measurement; phase transitions; superlattices; X-ray diffraction; crystal structure; dielectric oxides; heterojunctions; epitaxy; metallic thin films; thin film structure
OSTI Identifier:
1465322
Alternate Identifier(s):
OSTI ID: 1361745

Brahlek, M., Choquette, A. K., Smith, C. R., Engel-Herbert, R., and May, S. J.. Structural refinement of Pbnm-type perovskite films from analysis of half-order diffraction peaks. United States: N. p., Web. doi:10.1063/1.4974362.
Brahlek, M., Choquette, A. K., Smith, C. R., Engel-Herbert, R., & May, S. J.. Structural refinement of Pbnm-type perovskite films from analysis of half-order diffraction peaks. United States. doi:10.1063/1.4974362.
Brahlek, M., Choquette, A. K., Smith, C. R., Engel-Herbert, R., and May, S. J.. 2017. "Structural refinement of Pbnm-type perovskite films from analysis of half-order diffraction peaks". United States. doi:10.1063/1.4974362. https://www.osti.gov/servlets/purl/1465322.
@article{osti_1465322,
title = {Structural refinement of Pbnm-type perovskite films from analysis of half-order diffraction peaks},
author = {Brahlek, M. and Choquette, A. K. and Smith, C. R. and Engel-Herbert, R. and May, S. J.},
abstractNote = {Engineering structural modifications of epitaxial perovskite thin films is an effective route to induce new functionalities or enhance existing properties due to the close relation of the electronic ground state to the local bonding environment. As such, there is a necessity to systematically refine and precisely quantify these structural displacements, particularly those of the oxygen octahedra, which is a challenge due to the weak scattering factor of oxygen and the small diffraction volume of thin films. In this paper, we present an optimized algorithm to refine the octahedral rotation angles using specific unit-cell-doubling half-order diffraction peaks for the a-a-c+ Pbnm structure. The oxygen and A-site positions can be obtained by minimizing the squared-error between calculated and experimentally determined peak intensities using the (1/2 1/2 3/2) and (1/2 1/2 5/2) reflections to determine the rotation angle α about in-plane axes and the (1/2 5/2 1), (1/2 3/2 1), and (1/2 3/2 2) reflections to determine the rotation angle γ about the out-of-plane axis, whereas the convoluting A-site displacements associated with the octahedral rotation pattern can be determined using (1 1 1/2) and (1/2 1/2 1/2) reflections to independently determine A-site positions. The validity of the approach is confirmed by applying the refinement procedure to determine the A-site and oxygen displacements in a NdGaO3 single crystal. Finally, the ability to refine both the oxygen and A-site displacements relative to the undistorted perovskite structure enables a deeper understanding of how structural modifications alter functionality properties in epitaxial films exhibiting this commonly occurring crystal structure.},
doi = {10.1063/1.4974362},
journal = {Journal of Applied Physics},
number = 4,
volume = 121,
place = {United States},
year = {2017},
month = {1}
}