Structural investigation of GeSb₆Te₁₀ and GeBi₆Te₁₀ intermetallic compounds in the chalcogenide homologous series

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 (). 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.

Computing details

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)

Crystal data

GeSb6Te10	Z = 3
Mr = 2079.1	F(000) = 2574
Trigonal, R3m	Dx = 6.564 Mg m^−3
Hall symbol: -R 3;-2"	Synchrotron radiation, λ = 0.42354 Å
a = 4.236 Å	µ = 5.42 mm^−1
c = 101.5087 Å	T = 92 K
V = 1577.38 Å^3

Data collection

BL02B2 diffractometer	Data collection mode: transmission
Specimen mounting: 0.3mm diameter quartz capillary	Scan method: Stationary detector

Refinement

Rp = 0.041	39 parameters
Rwp = 0.057	19 restraints
Rexp = 0.012	Weighting scheme based on measured s.u.'s
R(F) = 0.040	(Δ/σ)max = 13.972
5481 data points	Background function: 15 Legendre polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: March & Dollase

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ge1	0	0	0	0.0190 (4)*	0.50 (3)
Te1	0	0	0.05337 (4)	0.0056 (2)*
Te2	0	0	0.11698 (6)	0.0056 (2)*
Te3	0	0	0.17986 (4)	0.0056 (2)*
Ge2	0	0	0.23559 (6)	0.0190 (4)*	0.02 (2)
Ge3	0	0	0.29560 (5)	0.0190 (4)*	0.18 (2)
Te4	0	0	0.35090 (5)	0.0056 (2)*
Te5	0	0	0.41426 (5)	0.0056 (2)*
Ge4	0	0	0.46956 (6)	0.0190 (4)*	0.05 (4)
Sb1	0	0	0	0.0190 (4)*	0.50 (3)
Sb2	0	0	0.23559 (6)	0.0190 (4)*	0.98 (2)
Sb3	0	0	0.29560 (5)	0.0190 (4)*	0.82 (2)
Sb4	0	0	0.46956 (6)	0.0190 (4)*	0.95 (4)

(II)

Crystal data

Bi6GeTe10	Z = 3
Mr = 2602.5	F(000) = 3150
Trigonal, R3m	Dx = 7.758 Mg m^−3
Hall symbol: -R 3;-2"	Synchrotron radiation, λ = 0.42308 Å
a = 4.3515 Å	µ = 15.89 mm^−1
c = 101.8739 Å	T = 92 K
V = 1670.57 Å^3

Data collection

BL02B2 diffractometer	Data collection mode: transmission
Specimen mounting: 0.2mm diameter quartz capillary	Scan method: Stationary detector

Refinement

Rp = 0.027	39 parameters
Rwp = 0.038	19 restraints
Rexp = 0.010	Weighting scheme based on measured s.u.'s
R(F) = 0.055	(Δ/σ)max = 8.549
5291 data points	Background function: 15 Legendre polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: March & Dollase

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ge1	0	0	0	0.0115 (4)*	0.459 (15)
Te1	0	0	0.05496 (7)	0.0144 (6)*
Te2	0	0	0.11734 (10)	0.0144 (6)*
Te3	0	0	0.17881 (7)	0.0144 (6)*
Ge2	0	0	0.23663 (4)	0.0115 (4)*	0.058 (12)
Ge3	0	0	0.29552 (4)	0.0115 (4)*	0.180 (9)
Te4	0	0	0.35089 (9)	0.0144 (6)*
Te5	0	0	0.41407 (9)	0.0144 (6)*
Ge4	0	0	0.46986 (4)	0.0115 (4)*	0.033 (17)
Bi1	0	0	0	0.0115 (4)*	0.541 (15)
Bi2	0	0	0.23663 (4)	0.0115 (4)*	0.942 (12)
Bi3	0	0	0.29552 (4)	0.0115 (4)*	0.820 (9)
Bi4	0	0	0.46986 (4)	0.0115 (4)*	0.967 (17)