A -site cation size effect on oxygen octahedral rotations in acentric Ruddlesden-Popper alkali rare-earth titanates

Hirofumi Akamatsu, Koji Fujita, Toshihiro Kuge, Arnab Sen Gupta, James M. Rondinelli, Isao Tanaka, Katsuhisa Tanaka, Venkatraman Gopalan

研究成果: ジャーナルへの寄稿記事

抄録

We demonstrate inversion symmetry breaking induced by oxygen octahedral rotations in layered perovskite oxides KARTiO4 (AR = rare earth) using a combined experimental and theoretical approach including synchrotron x-ray diffraction, optical second harmonic generation, and first-principles lattice dynamics calculations. We experimentally find an interesting but counterintuitive phenomenon, i.e., the acentric-to-centric phase transition temperatures for K family are higher than those for previously reported Na family, in contrast to expectations based on the Goldschmidt tolerance factor, where the octahedral rotation instability toward the acentric phases would reduce with an increase in the radius of A-site alkali metal ions. Our detailed analysis of first-principles calculations for AAARTiO4 (AA=Na, K, Rb) reveals that the alkali metal and rare-earth ions play quite different roles in driving the octahedral rotations. Since rare-earth ions attract oxide ions more strongly than alkali metal ions due to the higher valence of the former in comparison with the latter (AR3+ vs AA+), the optimization of coordination environment of rare-earth ions is the primary driving force of the octahedral rotations. Alkali metal ions serve to impose "bond strains" parallel to the layers, playing a secondary role in the octahedral rotations. Incorporation of large alkali metal ions generates a significant in-plane biaxial bond strain in ARO and TiO2 layers through the expanded AAO layers, and thereby facilitates the octahedral rotations because of the otherwise highly underbonding of rare-earth ions. Thus, the effect of A-site alkali metal size on the octahedral rotation instability can be explained in terms of the interlayer lattice mismatch. This understanding allows us to propose a geometric descriptor governing the structural instability in AAARTiO4 layered perovskites. We believe that control over the interlayer lattice mismatch could be a useful strategy to tune the octahedral rotations in layered compounds.

元の言語英語
記事番号065001
ジャーナルPhysical Review Materials
3
発行部数6
DOI
出版物ステータス出版済み - 6 10 2019

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titanates
Alkalies
Alkali Metals
Rare earths
Cations
alkalies
Alkali metals
rare earth elements
Positive ions
alkali metals
Oxygen
cations
oxygen
Metal ions
Ions
metal ions
Lattice mismatch
ions
Oxides
interlayers

All Science Journal Classification (ASJC) codes

  • Materials Science(all)
  • Physics and Astronomy (miscellaneous)

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A -site cation size effect on oxygen octahedral rotations in acentric Ruddlesden-Popper alkali rare-earth titanates. / Akamatsu, Hirofumi; Fujita, Koji; Kuge, Toshihiro; Gupta, Arnab Sen; Rondinelli, James M.; Tanaka, Isao; Tanaka, Katsuhisa; Gopalan, Venkatraman.

:: Physical Review Materials, 巻 3, 番号 6, 065001, 10.06.2019.

研究成果: ジャーナルへの寄稿記事

Akamatsu, Hirofumi ; Fujita, Koji ; Kuge, Toshihiro ; Gupta, Arnab Sen ; Rondinelli, James M. ; Tanaka, Isao ; Tanaka, Katsuhisa ; Gopalan, Venkatraman. / A -site cation size effect on oxygen octahedral rotations in acentric Ruddlesden-Popper alkali rare-earth titanates. :: Physical Review Materials. 2019 ; 巻 3, 番号 6.
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abstract = "We demonstrate inversion symmetry breaking induced by oxygen octahedral rotations in layered perovskite oxides KARTiO4 (AR = rare earth) using a combined experimental and theoretical approach including synchrotron x-ray diffraction, optical second harmonic generation, and first-principles lattice dynamics calculations. We experimentally find an interesting but counterintuitive phenomenon, i.e., the acentric-to-centric phase transition temperatures for K family are higher than those for previously reported Na family, in contrast to expectations based on the Goldschmidt tolerance factor, where the octahedral rotation instability toward the acentric phases would reduce with an increase in the radius of A-site alkali metal ions. Our detailed analysis of first-principles calculations for AAARTiO4 (AA=Na, K, Rb) reveals that the alkali metal and rare-earth ions play quite different roles in driving the octahedral rotations. Since rare-earth ions attract oxide ions more strongly than alkali metal ions due to the higher valence of the former in comparison with the latter (AR3+ vs AA+), the optimization of coordination environment of rare-earth ions is the primary driving force of the octahedral rotations. Alkali metal ions serve to impose {"}bond strains{"} parallel to the layers, playing a secondary role in the octahedral rotations. Incorporation of large alkali metal ions generates a significant in-plane biaxial bond strain in ARO and TiO2 layers through the expanded AAO layers, and thereby facilitates the octahedral rotations because of the otherwise highly underbonding of rare-earth ions. Thus, the effect of A-site alkali metal size on the octahedral rotation instability can be explained in terms of the interlayer lattice mismatch. This understanding allows us to propose a geometric descriptor governing the structural instability in AAARTiO4 layered perovskites. We believe that control over the interlayer lattice mismatch could be a useful strategy to tune the octahedral rotations in layered compounds.",
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T1 - A -site cation size effect on oxygen octahedral rotations in acentric Ruddlesden-Popper alkali rare-earth titanates

AU - Akamatsu, Hirofumi

AU - Fujita, Koji

AU - Kuge, Toshihiro

AU - Gupta, Arnab Sen

AU - Rondinelli, James M.

AU - Tanaka, Isao

AU - Tanaka, Katsuhisa

AU - Gopalan, Venkatraman

PY - 2019/6/10

Y1 - 2019/6/10

N2 - We demonstrate inversion symmetry breaking induced by oxygen octahedral rotations in layered perovskite oxides KARTiO4 (AR = rare earth) using a combined experimental and theoretical approach including synchrotron x-ray diffraction, optical second harmonic generation, and first-principles lattice dynamics calculations. We experimentally find an interesting but counterintuitive phenomenon, i.e., the acentric-to-centric phase transition temperatures for K family are higher than those for previously reported Na family, in contrast to expectations based on the Goldschmidt tolerance factor, where the octahedral rotation instability toward the acentric phases would reduce with an increase in the radius of A-site alkali metal ions. Our detailed analysis of first-principles calculations for AAARTiO4 (AA=Na, K, Rb) reveals that the alkali metal and rare-earth ions play quite different roles in driving the octahedral rotations. Since rare-earth ions attract oxide ions more strongly than alkali metal ions due to the higher valence of the former in comparison with the latter (AR3+ vs AA+), the optimization of coordination environment of rare-earth ions is the primary driving force of the octahedral rotations. Alkali metal ions serve to impose "bond strains" parallel to the layers, playing a secondary role in the octahedral rotations. Incorporation of large alkali metal ions generates a significant in-plane biaxial bond strain in ARO and TiO2 layers through the expanded AAO layers, and thereby facilitates the octahedral rotations because of the otherwise highly underbonding of rare-earth ions. Thus, the effect of A-site alkali metal size on the octahedral rotation instability can be explained in terms of the interlayer lattice mismatch. This understanding allows us to propose a geometric descriptor governing the structural instability in AAARTiO4 layered perovskites. We believe that control over the interlayer lattice mismatch could be a useful strategy to tune the octahedral rotations in layered compounds.

AB - We demonstrate inversion symmetry breaking induced by oxygen octahedral rotations in layered perovskite oxides KARTiO4 (AR = rare earth) using a combined experimental and theoretical approach including synchrotron x-ray diffraction, optical second harmonic generation, and first-principles lattice dynamics calculations. We experimentally find an interesting but counterintuitive phenomenon, i.e., the acentric-to-centric phase transition temperatures for K family are higher than those for previously reported Na family, in contrast to expectations based on the Goldschmidt tolerance factor, where the octahedral rotation instability toward the acentric phases would reduce with an increase in the radius of A-site alkali metal ions. Our detailed analysis of first-principles calculations for AAARTiO4 (AA=Na, K, Rb) reveals that the alkali metal and rare-earth ions play quite different roles in driving the octahedral rotations. Since rare-earth ions attract oxide ions more strongly than alkali metal ions due to the higher valence of the former in comparison with the latter (AR3+ vs AA+), the optimization of coordination environment of rare-earth ions is the primary driving force of the octahedral rotations. Alkali metal ions serve to impose "bond strains" parallel to the layers, playing a secondary role in the octahedral rotations. Incorporation of large alkali metal ions generates a significant in-plane biaxial bond strain in ARO and TiO2 layers through the expanded AAO layers, and thereby facilitates the octahedral rotations because of the otherwise highly underbonding of rare-earth ions. Thus, the effect of A-site alkali metal size on the octahedral rotation instability can be explained in terms of the interlayer lattice mismatch. This understanding allows us to propose a geometric descriptor governing the structural instability in AAARTiO4 layered perovskites. We believe that control over the interlayer lattice mismatch could be a useful strategy to tune the octahedral rotations in layered compounds.

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