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The crystal structures of GeSb6Te10 and GeBi6Te10 were scrutinized using an X-ray powder diffraction method, which revealed that these compounds crystallize in trigonally distorted cubic close-packed structures with a 51-layer period (R\bar 3m). Each layer consists of a triangular atomic net; Te atoms occupy their own specific layers, whereas Ge, Sb and Bi atoms are located in the other layers. In these pseudobinary compounds, random atomic occupations of Ge and Sb/Bi are observed and the layers form two kinds of elemental structural blocks by their successive stacking along the c axis. These compounds can be presumed to be isostructural. It is known that the chemical formula of the chalcogenide compounds with the homologous structures found in these pseudobinary systems can be written as (GeTe)n(Sb2Te3)m or (GeTe)n(Bi2Te3)m (n, m: integer); the GeSb6Te10 and GeBi6Te10 investigated in this study, which correspond to the case in which n = 1 and m = 3, naturally have 3 × l = 51-layer structures according to a formation rule l = 2n + 5m commonly found in the compounds of these chalcogenide systems (l represents the number of layers in the basic structural unit). Calculations based on the density functional theory revealed that these materials are compound semiconductors with very narrow band gaps.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108768110024080/so5032sup1.cif
Contains datablocks global, I, II

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768110024080/so5032Isup2.rtv
Contains datablock I

rtv

Rietveld powder data file (CIF format) https://doi.org/10.1107/S0108768110024080/so5032IIsup3.rtv
Contains datablock II

pdf

Portable Document Format (PDF) file https://doi.org/10.1107/S0108768110024080/so5032sup4.pdf
Tables of topological parameters, atom charges, delocalization effects, Wiberg bond indices and radial deformation parameters

Computing details top

For both structures, program(s) used to refine structure: Jana2000 (Petricek, Dusek & Palatinus, 2000); software used to prepare material for publication: Jana2000 (Petricek, Dusek & Palatinus, 2000).

(I) top
Crystal data top
GeSb6Te10Z = 3
Mr = 2079.1F(000) = 2574
Trigonal, R3mDx = 6.564 Mg m3
Hall symbol: -R 3;-2"Synchrotron radiation, λ = 0.42354 Å
a = 4.236 ŵ = 5.42 mm1
c = 101.5087 ÅT = 92 K
V = 1577.38 Å3
Data collection top
BL02B2
diffractometer
Data collection mode: transmission
Specimen mounting: 0.3mm diameter quartz capillaryScan method: Stationary detector
Refinement top
Rp = 0.04139 parameters
Rwp = 0.05719 restraints
Rexp = 0.012Weighting scheme based on measured s.u.'s
R(F) = 0.040(Δ/σ)max = 13.972
5481 data pointsBackground function: 15 Legendre polynoms
Profile function: Pseudo-VoigtPreferred orientation correction: March & Dollase
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ge10000.0190 (4)*0.50 (3)
Te1000.05337 (4)0.0056 (2)*
Te2000.11698 (6)0.0056 (2)*
Te3000.17986 (4)0.0056 (2)*
Ge2000.23559 (6)0.0190 (4)*0.02 (2)
Ge3000.29560 (5)0.0190 (4)*0.18 (2)
Te4000.35090 (5)0.0056 (2)*
Te5000.41426 (5)0.0056 (2)*
Ge4000.46956 (6)0.0190 (4)*0.05 (4)
Sb10000.0190 (4)*0.50 (3)
Sb2000.23559 (6)0.0190 (4)*0.98 (2)
Sb3000.29560 (5)0.0190 (4)*0.82 (2)
Sb4000.46956 (6)0.0190 (4)*0.95 (4)
(II) top
Crystal data top
Bi6GeTe10Z = 3
Mr = 2602.5F(000) = 3150
Trigonal, R3mDx = 7.758 Mg m3
Hall symbol: -R 3;-2"Synchrotron radiation, λ = 0.42308 Å
a = 4.3515 ŵ = 15.89 mm1
c = 101.8739 ÅT = 92 K
V = 1670.57 Å3
Data collection top
BL02B2
diffractometer
Data collection mode: transmission
Specimen mounting: 0.2mm diameter quartz capillaryScan method: Stationary detector
Refinement top
Rp = 0.02739 parameters
Rwp = 0.03819 restraints
Rexp = 0.010Weighting scheme based on measured s.u.'s
R(F) = 0.055(Δ/σ)max = 8.549
5291 data pointsBackground function: 15 Legendre polynoms
Profile function: Pseudo-VoigtPreferred orientation correction: March & Dollase
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Ge10000.0115 (4)*0.459 (15)
Te1000.05496 (7)0.0144 (6)*
Te2000.11734 (10)0.0144 (6)*
Te3000.17881 (7)0.0144 (6)*
Ge2000.23663 (4)0.0115 (4)*0.058 (12)
Ge3000.29552 (4)0.0115 (4)*0.180 (9)
Te4000.35089 (9)0.0144 (6)*
Te5000.41407 (9)0.0144 (6)*
Ge4000.46986 (4)0.0115 (4)*0.033 (17)
Bi10000.0115 (4)*0.541 (15)
Bi2000.23663 (4)0.0115 (4)*0.942 (12)
Bi3000.29552 (4)0.0115 (4)*0.820 (9)
Bi4000.46986 (4)0.0115 (4)*0.967 (17)
 

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