The mediation of bond strain by vacancies and displacive disorder in A-site-deficient perovskites

I. Levin; V. Krayzman; H. Y. Playford; J. C. Woicik; R. A. Maier; Z. Lu; A. Bruma; M. Eremenko; M. G. Tucker

doi:10.1016/j.actamat.2021.116678

The mediation of bond strain by vacancies and displacive disorder in A-site-deficient perovskites

I. Levin, V. Krayzman, H. Y. Playford, J. C. Woicik, R. A. Maier, Z. Lu, A. Bruma, M. Eremenko, M. G. Tucker

Research output: Contribution to journal › Article › peer-review

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Abstract

Local distortions in perovskite-like A-site-deficient (Sr,La)TiO₃ solid solutions have been determined by refining large-scale atomic configurations against neutron/X-ray total-scattering and extended-X-ray-absorption-fine-structure data. Structural relaxations in this system are driven by the competing bonding requirements of Sr, La, and the undercoordinated oxygen atoms that surround vacant A-sites, which form upon substitution of La for Sr. La cations exhibit significant, disordered off-center displacements within their oversized oxygen cages required by the larger Sr cations. The resulting split-site probability density distributions of La vary with the Sr/La ratio and the state of the A-site ordering, which together modify the structure's ability to relieve the tensile bond strain around La through octahedral rotation and displacements of oxygens surrounding the vacancies. The displacive disorder of La can provide a hitherto overlooked mechanism for reducing the thermal conductivity, which is relevant to thermoelectric properties of this system. A comparison of the local structural behaviors in (Sr,La)TiO₃ and the previously studied (Na,Bi)NbO₃ solid solutions permits generalizations about A-site deficient perovskites. We find that A-site vacancies provide the nearest-neighbor oxygens with a degree of freedom to mediate the strain in the system, and their effects on local structural relaxations are determined by cation chemistry and stoichiometry.

Original language	English
Article number	116678
Journal	Acta Materialia
Volume	207
DOIs	https://doi.org/10.1016/j.actamat.2021.116678
State	Published - Apr 1 2021
Externally published	Yes

Funding

Experiments at the ISIS Pulsed Neutron and Muon Source were supported by a beamtime allocation from the Science and Technology Facilities Council. A portion of this work was carried out with the support of the Diamond Light Source, Ltd. The authors are grateful to D. Keeble for his technical assistance with the X-ray total scattering measurements. This research also used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. MRCAT operations at this facility are supported by the Department of Energy and the MRCAT member institutions. We thank J. Wright for his technical assistance with the EXAFS measurements. Experiments at the ISIS Pulsed Neutron and Muon Source were supported by a beamtime allocation from the Science and Technology Facilities Council. A portion of this work was carried out with the support of the Diamond Light Source, Ltd. The authors are grateful to D. Keeble for his technical assistance with the X-ray total scattering measurements. This research also used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357 . MRCAT operations at this facility are supported by the Department of Energy and the MRCAT member institutions. We thank J. Wright for his technical assistance with the EXAFS measurements.

Funders	Funder number
Diamond Light Source, Ltd
ISIS
U.S. Department of Energy
Office of Science
Argonne National Laboratory	DE-AC02-06CH11357
Science and Technology Facilities Council

Keywords

Local structure
Neutron scattering, X-ray scattering, EXAFS
Perovskite
Thermoelectrics
Vacancies

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10.1016/j.actamat.2021.116678

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title = "The mediation of bond strain by vacancies and displacive disorder in A-site-deficient perovskites",

abstract = "Local distortions in perovskite-like A-site-deficient (Sr,La)TiO3 solid solutions have been determined by refining large-scale atomic configurations against neutron/X-ray total-scattering and extended-X-ray-absorption-fine-structure data. Structural relaxations in this system are driven by the competing bonding requirements of Sr, La, and the undercoordinated oxygen atoms that surround vacant A-sites, which form upon substitution of La for Sr. La cations exhibit significant, disordered off-center displacements within their oversized oxygen cages required by the larger Sr cations. The resulting split-site probability density distributions of La vary with the Sr/La ratio and the state of the A-site ordering, which together modify the structure's ability to relieve the tensile bond strain around La through octahedral rotation and displacements of oxygens surrounding the vacancies. The displacive disorder of La can provide a hitherto overlooked mechanism for reducing the thermal conductivity, which is relevant to thermoelectric properties of this system. A comparison of the local structural behaviors in (Sr,La)TiO3 and the previously studied (Na,Bi)NbO3 solid solutions permits generalizations about A-site deficient perovskites. We find that A-site vacancies provide the nearest-neighbor oxygens with a degree of freedom to mediate the strain in the system, and their effects on local structural relaxations are determined by cation chemistry and stoichiometry.",

keywords = "Local structure, Neutron scattering, X-ray scattering, EXAFS, Perovskite, Thermoelectrics, Vacancies",

author = "I. Levin and V. Krayzman and Playford, {H. Y.} and Woicik, {J. C.} and Maier, {R. A.} and Z. Lu and A. Bruma and M. Eremenko and Tucker, {M. G.}",

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AU - Levin, I.

AU - Krayzman, V.

AU - Playford, H. Y.

AU - Woicik, J. C.

AU - Maier, R. A.

AU - Lu, Z.

AU - Bruma, A.

AU - Eremenko, M.

AU - Tucker, M. G.

PY - 2021/4/1

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N2 - Local distortions in perovskite-like A-site-deficient (Sr,La)TiO3 solid solutions have been determined by refining large-scale atomic configurations against neutron/X-ray total-scattering and extended-X-ray-absorption-fine-structure data. Structural relaxations in this system are driven by the competing bonding requirements of Sr, La, and the undercoordinated oxygen atoms that surround vacant A-sites, which form upon substitution of La for Sr. La cations exhibit significant, disordered off-center displacements within their oversized oxygen cages required by the larger Sr cations. The resulting split-site probability density distributions of La vary with the Sr/La ratio and the state of the A-site ordering, which together modify the structure's ability to relieve the tensile bond strain around La through octahedral rotation and displacements of oxygens surrounding the vacancies. The displacive disorder of La can provide a hitherto overlooked mechanism for reducing the thermal conductivity, which is relevant to thermoelectric properties of this system. A comparison of the local structural behaviors in (Sr,La)TiO3 and the previously studied (Na,Bi)NbO3 solid solutions permits generalizations about A-site deficient perovskites. We find that A-site vacancies provide the nearest-neighbor oxygens with a degree of freedom to mediate the strain in the system, and their effects on local structural relaxations are determined by cation chemistry and stoichiometry.

AB - Local distortions in perovskite-like A-site-deficient (Sr,La)TiO3 solid solutions have been determined by refining large-scale atomic configurations against neutron/X-ray total-scattering and extended-X-ray-absorption-fine-structure data. Structural relaxations in this system are driven by the competing bonding requirements of Sr, La, and the undercoordinated oxygen atoms that surround vacant A-sites, which form upon substitution of La for Sr. La cations exhibit significant, disordered off-center displacements within their oversized oxygen cages required by the larger Sr cations. The resulting split-site probability density distributions of La vary with the Sr/La ratio and the state of the A-site ordering, which together modify the structure's ability to relieve the tensile bond strain around La through octahedral rotation and displacements of oxygens surrounding the vacancies. The displacive disorder of La can provide a hitherto overlooked mechanism for reducing the thermal conductivity, which is relevant to thermoelectric properties of this system. A comparison of the local structural behaviors in (Sr,La)TiO3 and the previously studied (Na,Bi)NbO3 solid solutions permits generalizations about A-site deficient perovskites. We find that A-site vacancies provide the nearest-neighbor oxygens with a degree of freedom to mediate the strain in the system, and their effects on local structural relaxations are determined by cation chemistry and stoichiometry.

KW - Local structure

KW - Neutron scattering, X-ray scattering, EXAFS

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The mediation of bond strain by vacancies and displacive disorder in A-site-deficient perovskites

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