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Title: Suppressed dependence of polarization on epitaxial strain in highly polar ferroelectrics.

Abstract

A combined experimental and computational investigation of coupling between polarization and epitaxial strain in highly polar ferroelectric PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT) thin films is reported. A comparison of the properties of relaxed (tetragonality c/a{approx}1.05) and highly strained (c/a{approx}1.09) epitaxial films shows that polarization, while being amongst the highest reported for PZT or PbTiO{sub 3} in either film or bulk forms (P{sub r}{approx}82 {mu}C/cm{sup 2}), is almost independent of the epitaxial strain. We attribute this behavior to a suppressed sensitivity of the A-site cations to epitaxial strain in these Pb-based perovskites, where the ferroelectric displacements are already large, contrary to the case of less polar perovskites, such as BaTiO{sub 3}. In the latter case, the A-site cation (Ba) and equatorial oxygen displacements can lead to substantial polarization increases.

Authors:
; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
953806
Report Number(s):
ANL/MSD/JA-59216
Journal ID: ISSN 0031-9007; PRLTAO; TRN: US201004%%565
DOE Contract Number:
DE-AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: Phys. Rev. Lett.; Journal Volume: 98; Journal Issue: 2007
Country of Publication:
United States
Language:
ENGLISH
Subject:
36 MATERIALS SCIENCE; CATIONS; COUPLING; EPITAXY; FERROELECTRIC MATERIALS; OXYGEN; PEROVSKITES; POLARIZATION; PZT; SENSITIVITY; STRAINS; THIN FILMS

Citation Formats

Lee, H. N., Nakhmanson, S. M., Chisholm, M. F., Christen, H. M., Rabe, K. M., Vanderbilt, D., Materials Science Division, ORNL, and Rutgers Univ.. Suppressed dependence of polarization on epitaxial strain in highly polar ferroelectrics.. United States: N. p., 2007. Web. doi:10.1103/PhysRevLett.98.217602.
Lee, H. N., Nakhmanson, S. M., Chisholm, M. F., Christen, H. M., Rabe, K. M., Vanderbilt, D., Materials Science Division, ORNL, & Rutgers Univ.. Suppressed dependence of polarization on epitaxial strain in highly polar ferroelectrics.. United States. doi:10.1103/PhysRevLett.98.217602.
Lee, H. N., Nakhmanson, S. M., Chisholm, M. F., Christen, H. M., Rabe, K. M., Vanderbilt, D., Materials Science Division, ORNL, and Rutgers Univ.. Mon . "Suppressed dependence of polarization on epitaxial strain in highly polar ferroelectrics.". United States. doi:10.1103/PhysRevLett.98.217602.
@article{osti_953806,
title = {Suppressed dependence of polarization on epitaxial strain in highly polar ferroelectrics.},
author = {Lee, H. N. and Nakhmanson, S. M. and Chisholm, M. F. and Christen, H. M. and Rabe, K. M. and Vanderbilt, D. and Materials Science Division and ORNL and Rutgers Univ.},
abstractNote = {A combined experimental and computational investigation of coupling between polarization and epitaxial strain in highly polar ferroelectric PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT) thin films is reported. A comparison of the properties of relaxed (tetragonality c/a{approx}1.05) and highly strained (c/a{approx}1.09) epitaxial films shows that polarization, while being amongst the highest reported for PZT or PbTiO{sub 3} in either film or bulk forms (P{sub r}{approx}82 {mu}C/cm{sup 2}), is almost independent of the epitaxial strain. We attribute this behavior to a suppressed sensitivity of the A-site cations to epitaxial strain in these Pb-based perovskites, where the ferroelectric displacements are already large, contrary to the case of less polar perovskites, such as BaTiO{sub 3}. In the latter case, the A-site cation (Ba) and equatorial oxygen displacements can lead to substantial polarization increases.},
doi = {10.1103/PhysRevLett.98.217602},
journal = {Phys. Rev. Lett.},
number = 2007,
volume = 98,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}
  • A combined experimental and computational investigation of coupling between polarization and epitaxial strain in highly polar ferroelectric PbZr{sub 0.2}Ti{sub 0.8}O{sub 3} (PZT) thin films is reported. A comparison of the properties of relaxed (tetragonality c/a{approx}1.05) and highly strained (c/a{approx}1.09) epitaxial films shows that polarization, while being amongst the highest reported for PZT or PbTiO3 in either film or bulk forms Pr{approx}82{micro}C/cm{sup 2}, is almost independent of the epitaxial strain. We attribute this behavior to a suppressed sensitivity of the A-site cations to epitaxial strain in these Pb-based perovskites, where the ferroelectric displacements are already large, contrary to the case ofmore » less polar perovskites, such as BaTiO{sub 3}. In the latter case, the A-site cation (Ba) and equatorial oxygen displacements can lead to substantial polarization increases.« less
  • Utilizing first-principles computational techniques, we have mapped out structural instabilities in the Ruddlesden-Popper homologous oxide superlattice families with a general chemical formula A{sub n-1}A{prime}2Ti{sub n}O{sub 3n+1}, A=Sr, Ba, and Pb (perovskite-type slab) and A{prime}=Sr (rocksalt-type insert) for n=1-5. Our calculations show that each superlattice family has a unique set of 'instability footprints', combining the ferroelectric, antiferroelectric, and antiferrodistortive types, and that the competition among the instabilities can be influenced by epitaxial strain and changing thickness of the perovskite-type slab, granting us wide flexibility to fine tune the properties of these materials for various device applications.
  • X-ray analysis of ferroelectric thin layers of Ba{sub 1/2}Sr{sub 1/2}TiO{sub 3} with different thicknesses reveals the presence of strain gradients across the films and allows us to propose a functional form for the internal strain profile. We use this to calculate the influence of strain gradient, through flexoelectric coupling, on the degradation of the ferroelectric properties of films with decreasing thickness, in excellent agreement with the observed behavior. This paper shows that strain relaxation can lead to smooth, continuous gradients across hundreds of nanometers, and it highlights the pressing need to avoid such strain gradients in order to obtain ferroelectricmore » films with bulklike properties.« less
  • Thin films of (00l) oriented SrBi{sub 2}Nb{sub 2}O{sub 9} epitaxially grown on SrTiO{sub 3} by sol-gel spin coating have been studied by means of high-resolution x-ray diffraction reciprocal space mapping. It is shown that these materials contain highly localized heterogeneous strain fields due to imperfect stacking faults (i.e., faults that do not propagate throughout the crystallites building up the film). In the film plane, the strain fields are confined to 11 nm wide regions and characterized by a vertical displacement of 0.18c (where c is the cell parameter) showing that the stacking faults are mainly composed of one additional (ormore » missing) perovskite layer. Prolonged thermal annealing at 700 deg. C strongly reduces the density of stacking faults and yields a more uniform strain distribution within the film volume without inducing significant grain growth.« less