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Conflict between the Electronic Factors and Structure-Directing Rules in the Intergrowth Structure of Ca4Ag2+xGe4-x with x = 1/2

Ponou, Siméon LU ; Lidin, Sven LU ; Grüner, Daniel and Miller, Gordon J. (2016) In Crystal Growth and Design 16(10). p.5946-5953
Abstract

Combined experimental and theoretical efforts to conceptually understand the structure directing forces in intergrowth structures have led to the discovery of the new ternary phase Ca4Ag2+xGe4-x (x = 0.5), obtained from high-temperature reaction of the elements. It crystallizes in a new structure type according to single-crystal diffraction methods: monoclinic space group C2/m-i10 with a = 10.7516(2) Å, b = 4.5475(1) Å, c = 18.7773(4) Å, β = 93.69(2)°, V = 916.17(3) Å3, Z = 4. The compound corresponds to the n = 2 member of the homologous series Ca2+nAg2+xGe2+n-x, that are built up by linear intergrowths of slabs cut from the CaGe (CrB-type) and the... (More)

Combined experimental and theoretical efforts to conceptually understand the structure directing forces in intergrowth structures have led to the discovery of the new ternary phase Ca4Ag2+xGe4-x (x = 0.5), obtained from high-temperature reaction of the elements. It crystallizes in a new structure type according to single-crystal diffraction methods: monoclinic space group C2/m-i10 with a = 10.7516(2) Å, b = 4.5475(1) Å, c = 18.7773(4) Å, β = 93.69(2)°, V = 916.17(3) Å3, Z = 4. The compound corresponds to the n = 2 member of the homologous series Ca2+nAg2+xGe2+n-x, that are built up by linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaAg1+xGe1-x (KHg2 or TiNiSi-type) structures, and may be partitioned in Ag-rich and Ag-free domains. Instead of the predicted Zr2CoSi2-type (C2/m-i5), a simultaneous doubling of the size of the two building blocks is observed with the dimerization of the (Ge2) pairs into Ag-substituted tetramers (AgxGe4-x) due to valence electron shortage. However, the Ag/Ge mixing at one atomic site with roughly one-to-one atomic ratio is therefore unexplained. The electronic band structure calculations and analysis of the chemical bonding provided evidence that the Ag/Ge mixing is rather the result of a direct conflict between the Zintl-Klemm concept and empirically established "structure-directing rules". The implications of these findings for the poorly understood ordered staging structural interfaces, typically observed in secondary Li-ion batteries during charge/discharge process, are briefly discussed.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Crystal Growth and Design
volume
16
issue
10
pages
8 pages
publisher
The American Chemical Society
external identifiers
  • scopus:84990060436
  • wos:000384952400042
ISSN
1528-7483
DOI
10.1021/acs.cgd.6b01002
language
English
LU publication?
yes
id
62a309ae-cae3-44b7-b4ae-d76615fa4501
date added to LUP
2016-10-21 07:41:31
date last changed
2017-01-01 08:37:21
@article{62a309ae-cae3-44b7-b4ae-d76615fa4501,
  abstract     = {<p>Combined experimental and theoretical efforts to conceptually understand the structure directing forces in intergrowth structures have led to the discovery of the new ternary phase Ca<sub>4</sub>Ag<sub>2+x</sub>Ge<sub>4-x</sub> (x = 0.5), obtained from high-temperature reaction of the elements. It crystallizes in a new structure type according to single-crystal diffraction methods: monoclinic space group C2/m-i<sup>10</sup> with a = 10.7516(2) Å, b = 4.5475(1) Å, c = 18.7773(4) Å, β = 93.69(2)°, V = 916.17(3) Å<sup>3</sup>, Z = 4. The compound corresponds to the n = 2 member of the homologous series Ca<sub>2+n</sub>Ag<sub>2+x</sub>Ge<sub>2+n-x</sub>, that are built up by linear intergrowths of slabs cut from the CaGe (CrB-type) and the CaAg<sub>1+x</sub>Ge<sub>1-x</sub> (KHg<sub>2</sub> or TiNiSi-type) structures, and may be partitioned in Ag-rich and Ag-free domains. Instead of the predicted Zr<sub>2</sub>CoSi<sub>2</sub>-type (C2/m-i<sup>5</sup>), a simultaneous doubling of the size of the two building blocks is observed with the dimerization of the (Ge<sub>2</sub>) pairs into Ag-substituted tetramers (Ag<sub>x</sub>Ge<sub>4-x</sub>) due to valence electron shortage. However, the Ag/Ge mixing at one atomic site with roughly one-to-one atomic ratio is therefore unexplained. The electronic band structure calculations and analysis of the chemical bonding provided evidence that the Ag/Ge mixing is rather the result of a direct conflict between the Zintl-Klemm concept and empirically established "structure-directing rules". The implications of these findings for the poorly understood ordered staging structural interfaces, typically observed in secondary Li-ion batteries during charge/discharge process, are briefly discussed.</p>},
  author       = {Ponou, Siméon and Lidin, Sven and Grüner, Daniel and Miller, Gordon J.},
  issn         = {1528-7483},
  language     = {eng},
  month        = {10},
  number       = {10},
  pages        = {5946--5953},
  publisher    = {The American Chemical Society},
  series       = {Crystal Growth and Design},
  title        = {Conflict between the Electronic Factors and Structure-Directing Rules in the Intergrowth Structure of Ca<sub>4</sub>Ag<sub>2+x</sub>Ge<sub>4-x</sub> with x = 1/2},
  url          = {http://dx.doi.org/10.1021/acs.cgd.6b01002},
  volume       = {16},
  year         = {2016},
}