Incommensurate-commensurate transition in the geometric ferroelectric LaTaO4

Grant William Howieson; Shitao Wu; Alexandra S Gibbs; Wuzong Zhou; James Floyd Scott; Finlay D. Morrison

doi:10.1002/adfm.202004667

Incommensurate-commensurate transition in the geometric ferroelectric LaTaO₄

Grant William Howieson, Shitao Wu, Alexandra S Gibbs, Wuzong Zhou, James Floyd Scott, Finlay D. Morrison

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

Abstract

The layered perovskite LaTaO₄ has been synthesized to be stable in both (polar) orthorhombic and (nonpolar) monoclinic polymorphs at ambient conditions. Although the structural transition between monoclinic and orthorhombic phases has been well established, there is some controversy regarding a further, unidentified transition around 500 K. Here this is identified as an incommensurate–commensurate first‐order transition between incommensurate Cmc2₁(α00)0s0 and commensurate Cmc2₁ orthorhombic phases. Transmission electron microscopy indicates partially ordered stacking of different structural units in a, identifying the local cause for the modulation, whereas variable temperature powder neutron diffraction has shown the overall macroscopic modulation vector, q ≈ (0.456, 0, 0)—roughly a 2.2 × expansion in a, corresponding to an approximate 11a commensurate superunit cell dimension. The modulation shows a continuous temperature dependence until transitioning to the basic (commensurate) cell at T_IC‐C. Doping the interlayer La sites with smaller Nd cations stabilizes the incommensuration to higher temperature, suggesting the modulation is geometrically driven at the A site.

Original language	English
Article number	2004667
Number of pages	10
Journal	Advanced Functional Materials
Volume	30
Issue number	45
Early online date	6 Sept 2020
DOIs	https://doi.org/10.1002/adfm.202004667
Publication status	Published - 4 Nov 2020

Keywords

Dielectrics
Ferroics
Structure-property relationships

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Howieson-2020-Incommensurate-commensurate-AFM-CC
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Cite this

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title = "Incommensurate-commensurate transition in the geometric ferroelectric LaTaO4",

abstract = "The layered perovskite LaTaO4 has been synthesized to be stable in both (polar) orthorhombic and (nonpolar) monoclinic polymorphs at ambient conditions. Although the structural transition between monoclinic and orthorhombic phases has been well established, there is some controversy regarding a further, unidentified transition around 500 K. Here this is identified as an incommensurate–commensurate first‐order transition between incommensurate Cmc21(α00)0s0 and commensurate Cmc21 orthorhombic phases. Transmission electron microscopy indicates partially ordered stacking of different structural units in a, identifying the local cause for the modulation, whereas variable temperature powder neutron diffraction has shown the overall macroscopic modulation vector, q ≈ (0.456, 0, 0)—roughly a 2.2 × expansion in a, corresponding to an approximate 11a commensurate superunit cell dimension. The modulation shows a continuous temperature dependence until transitioning to the basic (commensurate) cell at TIC‐C. Doping the interlayer La sites with smaller Nd cations stabilizes the incommensuration to higher temperature, suggesting the modulation is geometrically driven at the A site.",

keywords = "Dielectrics, Ferroics, Structure-property relationships",

author = "Howieson, {Grant William} and Shitao Wu and Gibbs, {Alexandra S} and Wuzong Zhou and Scott, {James Floyd} and Morrison, {Finlay D.}",

note = "Funding: UK Engineering and Physical Sciences Research Council (Grant Number(s): EP/P022637/1, EP/K503162/1), Science and Technology Facilities Council (Grant Number(s): RB1820307), China Scholarship Council (CN).",

year = "2020",

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doi = "10.1002/adfm.202004667",

language = "English",

volume = "30",

journal = "Advanced Functional Materials",

issn = "1616-301X",

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TY - JOUR

T1 - Incommensurate-commensurate transition in the geometric ferroelectric LaTaO4

AU - Howieson, Grant William

AU - Wu, Shitao

AU - Gibbs, Alexandra S

AU - Zhou, Wuzong

AU - Scott, James Floyd

AU - Morrison, Finlay D.

N1 - Funding: UK Engineering and Physical Sciences Research Council (Grant Number(s): EP/P022637/1, EP/K503162/1), Science and Technology Facilities Council (Grant Number(s): RB1820307), China Scholarship Council (CN).

PY - 2020/11/4

Y1 - 2020/11/4

N2 - The layered perovskite LaTaO4 has been synthesized to be stable in both (polar) orthorhombic and (nonpolar) monoclinic polymorphs at ambient conditions. Although the structural transition between monoclinic and orthorhombic phases has been well established, there is some controversy regarding a further, unidentified transition around 500 K. Here this is identified as an incommensurate–commensurate first‐order transition between incommensurate Cmc21(α00)0s0 and commensurate Cmc21 orthorhombic phases. Transmission electron microscopy indicates partially ordered stacking of different structural units in a, identifying the local cause for the modulation, whereas variable temperature powder neutron diffraction has shown the overall macroscopic modulation vector, q ≈ (0.456, 0, 0)—roughly a 2.2 × expansion in a, corresponding to an approximate 11a commensurate superunit cell dimension. The modulation shows a continuous temperature dependence until transitioning to the basic (commensurate) cell at TIC‐C. Doping the interlayer La sites with smaller Nd cations stabilizes the incommensuration to higher temperature, suggesting the modulation is geometrically driven at the A site.

AB - The layered perovskite LaTaO4 has been synthesized to be stable in both (polar) orthorhombic and (nonpolar) monoclinic polymorphs at ambient conditions. Although the structural transition between monoclinic and orthorhombic phases has been well established, there is some controversy regarding a further, unidentified transition around 500 K. Here this is identified as an incommensurate–commensurate first‐order transition between incommensurate Cmc21(α00)0s0 and commensurate Cmc21 orthorhombic phases. Transmission electron microscopy indicates partially ordered stacking of different structural units in a, identifying the local cause for the modulation, whereas variable temperature powder neutron diffraction has shown the overall macroscopic modulation vector, q ≈ (0.456, 0, 0)—roughly a 2.2 × expansion in a, corresponding to an approximate 11a commensurate superunit cell dimension. The modulation shows a continuous temperature dependence until transitioning to the basic (commensurate) cell at TIC‐C. Doping the interlayer La sites with smaller Nd cations stabilizes the incommensuration to higher temperature, suggesting the modulation is geometrically driven at the A site.

KW - Dielectrics

KW - Ferroics

KW - Structure-property relationships

UR - https://onlinelibrary.wiley.com/doi/10.1002/adfm.202004667

U2 - 10.1002/adfm.202004667

DO - 10.1002/adfm.202004667

M3 - Article

SN - 1616-301X

VL - 30

JO - Advanced Functional Materials

JF - Advanced Functional Materials

IS - 45

M1 - 2004667

ER -

Incommensurate-commensurate transition in the geometric ferroelectric LaTaO₄

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