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Origins of superstructure ordering and incommensurability in stuffed CoSn-type phases

Fredrickson, Daniel C. ; Lidin, Sven LU ; Venturini, Gerard ; Malaman, Bernard and Christensen, Jeppe LU (2008) In Journal of the American Chemical Society 130(26). p.8195-8214
Abstract

The CoSn structure type contains large interstitial void spaces that frequently host electropositive guest atoms, such as rare earth elements. In this stuffing process, an intriguing ordering occurs between the neighboring void spaces leading to a family of long-period superstructures comprising intergrowths of the ScFe6Ge6 and ScFe6Ga 6 structure types. This superstucture ordering culminates in incommensurability in the REFe6Ge6-δGa δ systems with RE = Sc, Tb, and Lu. In this work, we derive a 3 + 1D superspace model encompassing this series of structures and investigate the origins of the structural trends in this family with electronic structure... (More)

The CoSn structure type contains large interstitial void spaces that frequently host electropositive guest atoms, such as rare earth elements. In this stuffing process, an intriguing ordering occurs between the neighboring void spaces leading to a family of long-period superstructures comprising intergrowths of the ScFe6Ge6 and ScFe6Ga 6 structure types. This superstucture ordering culminates in incommensurability in the REFe6Ge6-δGa δ systems with RE = Sc, Tb, and Lu. In this work, we derive a 3 + 1D superspace model encompassing this series of structures and investigate the origins of the structural trends in this family with electronic structure calculations, at both the LDA-DFT and extended Hückel levels. Using our 3 + 1D model, we refine the structures of four new ErFe6Ge 6-δGaδ (0 ≤ δ ≤ 6) phases, two commensurate and two incommensurate, from powder X-ray diffraction data. The refinement results confirm trends observed in the Sc-, Tb-, and Lu-based series: a gradual lengthening and, eventually, turning of the q-vector as Ge is progressively exchanged for Ga. These trends, and the incommensurate ordering as a whole, are traced to a tension between two modes by which the host lattice responds to stuffing atom insertion: (1) an atomic charge modulation enhancing the anionic character of the cavity walls around the guest atoms, and (2) a positional modulation expanding the cavities occupied by guest atoms. These two modes direct the stuffing atom ordering pattern toward opposite ends of the ScFe6Ge6-ScFe6Ga6 intergrowth series. The full series of structures, complex and incommensurate, reflects various degrees of balance between these two factors.

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author
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organization
publishing date
type
Contribution to journal
publication status
published
in
Journal of the American Chemical Society
volume
130
issue
26
pages
20 pages
publisher
The American Chemical Society (ACS)
external identifiers
  • scopus:46049111636
ISSN
0002-7863
DOI
10.1021/ja077380+
language
English
LU publication?
yes
id
c709f9be-8faf-44fd-9e3a-fc502155d3cb
date added to LUP
2019-04-08 15:11:38
date last changed
2022-01-31 18:46:46
@article{c709f9be-8faf-44fd-9e3a-fc502155d3cb,
  abstract     = {{<p>The CoSn structure type contains large interstitial void spaces that frequently host electropositive guest atoms, such as rare earth elements. In this stuffing process, an intriguing ordering occurs between the neighboring void spaces leading to a family of long-period superstructures comprising intergrowths of the ScFe<sub>6</sub>Ge<sub>6</sub> and ScFe<sub>6</sub>Ga <sub>6</sub> structure types. This superstucture ordering culminates in incommensurability in the REFe<sub>6</sub>Ge<sub>6-δ</sub>Ga <sub>δ</sub> systems with RE = Sc, Tb, and Lu. In this work, we derive a 3 + 1D superspace model encompassing this series of structures and investigate the origins of the structural trends in this family with electronic structure calculations, at both the LDA-DFT and extended Hückel levels. Using our 3 + 1D model, we refine the structures of four new ErFe<sub>6</sub>Ge <sub>6-δ</sub>Ga<sub>δ</sub> (0 ≤ δ ≤ 6) phases, two commensurate and two incommensurate, from powder X-ray diffraction data. The refinement results confirm trends observed in the Sc-, Tb-, and Lu-based series: a gradual lengthening and, eventually, turning of the q-vector as Ge is progressively exchanged for Ga. These trends, and the incommensurate ordering as a whole, are traced to a tension between two modes by which the host lattice responds to stuffing atom insertion: (1) an atomic charge modulation enhancing the anionic character of the cavity walls around the guest atoms, and (2) a positional modulation expanding the cavities occupied by guest atoms. These two modes direct the stuffing atom ordering pattern toward opposite ends of the ScFe<sub>6</sub>Ge<sub>6</sub>-ScFe<sub>6</sub>Ga<sub>6</sub> intergrowth series. The full series of structures, complex and incommensurate, reflects various degrees of balance between these two factors.</p>}},
  author       = {{Fredrickson, Daniel C. and Lidin, Sven and Venturini, Gerard and Malaman, Bernard and Christensen, Jeppe}},
  issn         = {{0002-7863}},
  language     = {{eng}},
  month        = {{07}},
  number       = {{26}},
  pages        = {{8195--8214}},
  publisher    = {{The American Chemical Society (ACS)}},
  series       = {{Journal of the American Chemical Society}},
  title        = {{Origins of superstructure ordering and incommensurability in stuffed CoSn-type phases}},
  url          = {{http://dx.doi.org/10.1021/ja077380+}},
  doi          = {{10.1021/ja077380+}},
  volume       = {{130}},
  year         = {{2008}},
}