Anharmonic temperature factors up to sixth order and atomic potentials in the fast ionic conductor α-Ag3SI

Perenthaler, E.; Schulz, H.

doi:10.1016/0167-2738(81)90018-7

Cited by 20 publications

(8 citation statements)

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“…The structural model proposed here for α-Ag 3 SI differs somewhat from those proposed previously [15][16][17], in which the Ag + are found to predominantly occupy the octahedral and/or tetrahedral positions, implying that the Ag + diffusion pathways are in 100 directions. Unfortunately, the information provided by the G(r) data is relatively limited, with a shoulder at ∼2.60 Å and a peak at 2.88 Å as the only significant features.…”

Section: Discussioncontrasting

confidence: 83%

“…At temperatures above 519 K Ag 3 SI exists in its α-phase which is characterized by a random distribution of S 2− and I − over the 0, 0, 0 and 1/2, 1/2, 1/2 positions of a cubic unit cell with a ∼ 5.0 Å. The mobile Ag + are located predominantly near the octahedral cavities but undergo rapid diffusion along the 100 directions [15][16][17]. Samples which are slowly cooled to room temperature undergo an ordering of the two cation species over the 0, 0, 0 and 1/2, 1/2, 1/2 positions, such that the space group changes from I m3m to P m3m [16][17][18].…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, the compound has been widely studied as a model superionic system, to investigate the systematic variation of the superionic behaviour on increasing cation density across the series of b.c.c.-structured phases α-AgI → α-Ag 3 SI → β-Ag 2 S, in which the number of mobile cations per anion increases from 1 to 1.5 to 2. However, the exact nature of the Ag + distribution within the four phases α, α * , β and γ has been the subject of some debate within the literature [15][16][17][18][19][20][21] and this has motivated an extensive study of their crystallographic and transport properties by the authors. In this paper we report structural studies of the four phases of Ag 3 SI using powder neutron diffraction.…”

Section: Introductionmentioning

confidence: 99%

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The crystal structures of superionic Ag₃SI

Hull

Keen

Gardner

et al. 2001

J. Phys.: Condens. Matter

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The crystal structures of the four phases of the 'anti-perovskite' superionic conductor Ag 3 SI have been investigated by powder neutron diffraction and complex impedance spectroscopy. The high-temperature α-phase is characterized by a random distribution of the two cation species S 2− and I − over the 2(a) positions at 0, 0, 0 and 1/2, 1/2, 1/2 within space group I m3m. The Ag + are found to preferentially occupy the 24(h) trigonal interstices within the anion sublattice, though with significant anisotropy in their thermal vibrations. On quenching from high temperature the disordered cation array is retained, forming the metastable α * -phase, but there is a significant change in the cation distribution. The Ag + are predominantly located in 24(g) sites between the octahedral and tetrahedral cavities, though a significant proportion are found in 48(i) sites close to the 1/4, 1/4, 1/4 position midway between two anions. The latter are displaced by ∼0.7 Å in 110 directions to avoid short cation-anion contacts. Slow cooling from the α-phase followed by prolonged annealing at modest temperatures (∼473 K) stabilizes the β-phase of Ag 3 SI, in which longrange ordering of the two cation species lowers the symmetry to P m3m. The Ag + now occupy 12(h) positions close to half the octahedral sites, such that they do not form close contacts with the larger I − species. The displacements are in the four 100 directions and towards the tetrahedral sites, with a single Ag + randomly occupying one of these four 'split' positions. On cooling, the ionic conductivity is found to drop abruptly by ∼4× at T = 156(2) K at the β → γ transition. High-resolution powder neutron diffraction studies indicate that γ -Ag 3 SI possesses a very small rhombohedral distortion of the unit cell. The crystal structure of γ -Ag 3 SI (space group R3) can be derived from that of the β-phase by long-range ordering of the Ag + onto a subset of the displaced octahedral positions and an associated small displacement of the S 2− in a 111 direction.

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Section: Discussioncontrasting

confidence: 83%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The crystal structures of superionic Ag₃SI

Hull

Keen

Gardner

et al. 2001

J. Phys.: Condens. Matter

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“…0) and (t! 0) have been used as Ag "sites" in a structure refinement with anharmonic temperature factors (36,37). The result is presented in the form of a potential along the conduction paths (x -!…”

Section: Ix-a93s1mentioning

confidence: 99%

Crystal Structures of Fast Ion Conductors

Schulz¹

1982

Annu. Rev. Mater. Sci.

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“…Nowadays the accuracy and precision of diffraction data are in general no longer an obstacle to a meaningful refinement of such high-order thermal parameters in a least-squares procedure, e.g. CsPbCI3 (Hutton & Nelmes, 1981), Li3N , Ag3SI (Perenthaler & Schulz, 1981), PbF2 (Schulz, Perenthaler & Zucker, 1982), RbAg415 (Kuhs, 1983). Crystallographic program systems like PROMETHEUS (Zucker, Perenthaler, Kuhs, Bachmann & Schulz, 1983) allow for the routine insertion and refinement of parameters up to sixth order.…”

Section: Introductionmentioning

confidence: 99%