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Metastable Ge4Bi2Te7 is highly disordered; the average structure corresponds to the rocksalt type. The diffraction pattern shows diffuse streaks interconnecting Bragg reflections along all cubic 〈111〉 directions. These streaks exhibit satellite-like maxima and arise from vacancy ordering in non-periodically spaced defect layers. The atom layers near these vacancy layers are displaced with respect to the average structure: they tend to form α-GeTe-type double layers. The three-dimensional difference pair distribution function (3D-ΔPDF) method yields quantitative information on the distribution of defect layer spacings, which peaks at a value corresponding to Ge3Bi2Te6 building blocks. The cation distribution along with the displacement of the atom layers is refined as well, using a least-squares approach. Bi concentrates on cation positions next to the vacancy layers.
Supporting information
CCDC reference: 1040739
Program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997).
Crystal data top
Bi1.09Ge2.37Te4 | Synchrotron radiation, λ = 0.47686 Å |
Mr = 910.23 | Cell parameters from 410 reflections |
Cubic, Fm3m | θ = 3.9–20.1° |
a = 6.055 (2) Å | µ = 14.63 mm−1 |
V = 222.0 (2) Å3 | T = 293 K |
Z = 1 | Octahedron, metallic_dark_grey |
F(000) = 374 | 0.10 × 0.09 × 0.08 mm |
Dx = 6.807 Mg m−3 | |
Data collection top
Heavy duty (Huber) diffractometer | 47 reflections with I > 2σ(I) |
oscillation scans | Rint = 0.036 |
Absorption correction: multi-scan SADABS | θmax = 24.2°, θmin = 3.9° |
Tmin = 0.53, Tmax = 0.79 | h = −7→10 |
1161 measured reflections | k = −8→8 |
49 independent reflections | l = −10→8 |
Refinement top
Refinement on F2 | 1 restraint |
Least-squares matrix: full | Primary atom site location: model |
R[F2 > 2σ(F2)] = 0.016 | Secondary atom site location: none |
wR(F2) = 0.019 | w = 1/[σ2(Fo2) + (0.0052P)2 + 0.0547P] where P = (Fo2 + 2Fc2)/3 |
S = 1.35 | (Δ/σ)max < 0.001 |
49 reflections | Δρmax = 0.66 e Å−3 |
7 parameters | Δρmin = −1.74 e Å−3 |
Special details top
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell esds are taken
into account individually in the estimation of esds in distances, angles
and torsion angles; correlations between esds in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell esds is used for estimating esds involving l.s. planes. |
Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and
goodness of fit S are based on F2, conventional R-factors R are based
on F, with F set to zero for negative F2. The threshold expression of
F2 > 2sigma(F2) is used only for calculating R-factors(gt) etc. and is
not relevant to the choice of reflections for refinement. R-factors based
on F2 are statistically about twice as large as those based on F, and R-
factors based on ALL data will be even larger. |
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top | x | y | z | Uiso*/Ueq | Occ. (<1) |
Ge1 | 0.0228 (4) | 0.0228 (4) | 0.0228 (4) | 0.0298 (10) | 0.0740 (8) |
Bi1 | 0.0228 (4) | 0.0228 (4) | 0.0228 (4) | 0.0298 (10) | 0.0340 (5) |
Te2 | 0.5000 | 0.5000 | 0.5000 | 0.02721 (18)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Ge1 | 0.0298 (10) | 0.0298 (10) | 0.0298 (10) | 0.0026 (4) | 0.0026 (4) | 0.0026 (4) |
Bi1 | 0.0298 (10) | 0.0298 (10) | 0.0298 (10) | 0.0026 (4) | 0.0026 (4) | 0.0026 (4) |
Geometric parameters (Å, º) top
Ge1—Te2i | 2.896 (2) | Te2—Ge1vi | 2.896 (2) |
Ge1—Te2ii | 2.896 (2) | Te2—Bi1vii | 2.896 (2) |
Ge1—Te2iii | 2.896 (2) | Te2—Bi1viii | 2.896 (2) |
Te2—Bi1iv | 2.896 (2) | Te2—Bi1ix | 2.896 (2) |
Te2—Bi1v | 2.896 (2) | Te2—Bi1x | 2.896 (2) |
Te2—Bi1vi | 2.896 (2) | Te2—Ge1xi | 2.896 (2) |
Te2—Ge1iv | 2.896 (2) | Te2—Ge1xii | 2.896 (2) |
Te2—Ge1v | 2.896 (2) | | |
| | | |
Te2i—Ge1—Te2ii | 95.34 (9) | Ge1v—Te2—Bi1ix | 84.66 (9) |
Te2i—Ge1—Te2iii | 95.34 (9) | Ge1vi—Te2—Bi1ix | 5.47 (10) |
Te2ii—Ge1—Te2iii | 95.34 (9) | Bi1vii—Te2—Bi1ix | 7.75 (14) |
Bi1iv—Te2—Bi1v | 84.40 (10) | Bi1viii—Te2—Bi1ix | 90.131 (5) |
Bi1iv—Te2—Bi1vi | 84.40 (10) | Bi1iv—Te2—Bi1x | 5.47 (10) |
Bi1v—Te2—Bi1vi | 84.40 (10) | Bi1v—Te2—Bi1x | 84.66 (9) |
Bi1iv—Te2—Ge1iv | 0.00 (9) | Bi1vi—Te2—Bi1x | 89.869 (5) |
Bi1v—Te2—Ge1iv | 84.40 (10) | Ge1iv—Te2—Bi1x | 5.47 (10) |
Bi1vi—Te2—Ge1iv | 84.40 (10) | Ge1v—Te2—Bi1x | 84.66 (9) |
Bi1iv—Te2—Ge1v | 84.40 (10) | Ge1vi—Te2—Bi1x | 89.869 (5) |
Bi1v—Te2—Ge1v | 0.00 (9) | Bi1vii—Te2—Bi1x | 90.131 (5) |
Bi1vi—Te2—Ge1v | 84.40 (10) | Bi1viii—Te2—Bi1x | 84.40 (10) |
Ge1iv—Te2—Ge1v | 84.40 (10) | Bi1ix—Te2—Bi1x | 95.34 (9) |
Bi1iv—Te2—Ge1vi | 84.40 (10) | Bi1iv—Te2—Ge1xi | 5.47 (10) |
Bi1v—Te2—Ge1vi | 84.40 (10) | Bi1v—Te2—Ge1xi | 89.869 (5) |
Bi1vi—Te2—Ge1vi | 0.0 | Bi1vi—Te2—Ge1xi | 84.66 (9) |
Ge1iv—Te2—Ge1vi | 84.40 (10) | Ge1iv—Te2—Ge1xi | 5.47 (10) |
Ge1v—Te2—Ge1vi | 84.40 (10) | Ge1v—Te2—Ge1xi | 89.869 (5) |
Bi1iv—Te2—Bi1vii | 84.66 (9) | Ge1vi—Te2—Ge1xi | 84.66 (9) |
Bi1v—Te2—Bi1vii | 89.869 (5) | Bi1vii—Te2—Ge1xi | 84.40 (10) |
Bi1vi—Te2—Bi1vii | 5.47 (10) | Bi1viii—Te2—Ge1xi | 90.131 (5) |
Ge1iv—Te2—Bi1vii | 84.66 (9) | Bi1ix—Te2—Ge1xi | 90.131 (5) |
Ge1v—Te2—Bi1vii | 89.869 (5) | Bi1x—Te2—Ge1xi | 7.75 (14) |
Ge1vi—Te2—Bi1vii | 5.47 (10) | Bi1iv—Te2—Ge1xii | 89.869 (5) |
Bi1iv—Te2—Bi1viii | 84.66 (9) | Bi1v—Te2—Ge1xii | 5.47 (10) |
Bi1v—Te2—Bi1viii | 5.47 (10) | Bi1vi—Te2—Ge1xii | 84.66 (9) |
Bi1vi—Te2—Bi1viii | 89.869 (5) | Ge1iv—Te2—Ge1xii | 89.869 (5) |
Ge1iv—Te2—Bi1viii | 84.66 (9) | Ge1v—Te2—Ge1xii | 5.47 (10) |
Ge1v—Te2—Bi1viii | 5.47 (10) | Ge1vi—Te2—Ge1xii | 84.66 (9) |
Ge1vi—Te2—Bi1viii | 89.869 (5) | Bi1vii—Te2—Ge1xii | 90.131 (5) |
Bi1vii—Te2—Bi1viii | 95.34 (9) | Bi1viii—Te2—Ge1xii | 7.75 (14) |
Bi1iv—Te2—Bi1ix | 89.869 (5) | Bi1ix—Te2—Ge1xii | 84.40 (10) |
Bi1v—Te2—Bi1ix | 84.66 (9) | Bi1x—Te2—Ge1xii | 90.131 (5) |
Bi1vi—Te2—Bi1ix | 5.47 (10) | Ge1xi—Te2—Ge1xii | 95.34 (9) |
Ge1iv—Te2—Bi1ix | 89.869 (5) | | |
Symmetry codes: (i) x−1/2, y−1/2, z; (ii) x−1/2, y, z−1/2; (iii) x, y−1/2, z−1/2; (iv) x, −y+1/2, −z+1/2; (v) −x+1/2, y, −z+1/2; (vi) −x+1/2, −y+1/2, z; (vii) −x+1/2, y+1/2, z; (viii) −x+1/2, y, z+1/2; (ix) x+1/2, −y+1/2, z; (x) x, −y+1/2, z+1/2; (xi) x, y+1/2, −z+1/2; (xii) x+1/2, y, −z+1/2. |
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