Structures of stable and metastable Ge₂Bi₂Te₅, an intermetallic compound in a GeTe-Bi₂Te₃ pseudobinary system

Ge₂Bi₂Te₅ in the GeTe-Bi₂Te₃ pseudobinary system has two single-crystalline phases: a metastable phase with an NaCl-type structure and a stable phase with a nine-layer trigonal structure. In the metastable phase, the structure consists, in the hexagonal notation, of infinitely alternating stacks of Te and Ge/Bi layers at equal intervals along the c axis. On the other hand, in the stable phase those two layers are stacked alternately nine times to form an NaCl block. The blocks are then piled to construct a nine-layered trigonal structure with cubic close-packed stacking. Both ends of each block are covered with Te layers, contrary to the infinite alternation of Ge/Bi and Te layers in the structure of the metastable phase. The Ge/Bi layers in the metastable phase contain as much as 20 at. % vacancies; on the other hand, those in the stable phase are filled with atoms. These two crystalline phases in Ge₂Bi₂Te₅ have identical atomic configurations to the two corresponding phases found in Ge₂Sb₂Te₅.

S1. Experimental

Approximately 300 nm-thick Ge₂Bi₂Te₅ thin film was deposited onto a 120 mm-diameter glass disc at room temperature by DC magnetron sputtering from stoichiometric GeTe-Bi₂Te₃ compound target in an Ar gas atmosphere set at about 0.2 Pa.

Computing details

For all compounds, cell refinement: Rietan (Izumi, F. & Ikeda, T., 2000); data reduction: Rietan; program(s) used to solve structure: Rietan; program(s) used to refine structure: Rietan.

Figures

(metastable_87K)

Crystal data

Ge1.6Bi1.6Te4	Dx = 6.98 Mg m^−3
Mr = 960.83	Synchrotron, radiation radiation, λ = 0.42182 Å
Cubic, Fm3m	µ = 11.52 mm^−1
a = 6.0932 (5) Å	T = 87 K
V = 226.22 (3) Å^3	cylinder, 3.0 × 0.1 mm
Z = 1	Specimen preparation: Prepared at 300 K and 0.0002 kPa, cooled at 0 K min^−1

Data collection

Debye-Scherrer camera diffractometer	Specimen mounting: sealed quartz capillary tube
Radiation source: synchrotron	Data collection mode: transmission
Vertical focusing mirror + Si (111) double monochromator	Scan method: Stationary detector

Refinement

Refinement on Inet	Excluded region(s): none
Rp = 0.013	Profile function: pseudo-Voigt
Rwp = 0.018	28 parameters
Rexp = 0.028	Weighting scheme based on measured s.u.'s
RBragg = 0.005
χ^2 = 0.436	Background function: Legendre polynomial
7360 data points	Preferred orientation correction: March-Dollase function, axis (511)

Special details

Experimental. Japan Synchrotron Radiation Research Institute (SPring-8) 1–1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679–5198 Japan

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ge1	0.50000	0.50000	0.50000	0.0590 (18)*	0.3970 (58)
Bi1	0.50000	0.50000	0.50000	0.0590*	0.3970
Te1	0.00000	0.00000	0.00000	0.0261 (14)*

(metastable_293K)

Crystal data

Ge1.6Bi1.6Te4	Dx = 6.96 Mg m^−3
Mr = 960.83	Synchrotron, radiation radiation, λ = 0.42182 Å
Cubic, Fm3m	µ = 11.51 mm^−1
a = 6.1109 (9) Å	T = 293 K
V = 228.20 (6) Å^3	cylinder, 3.0 × 0.1 mm
Z = 1	Specimen preparation: Prepared at 300 K and 0.0002 kPa, cooled at 0 K min^−1

Data collection

Debye-Scherrer camera diffractometer	Specimen mounting: sealed quartz capillary tube
Radiation source: synchrotron	Data collection mode: transmission
Vertical focusing mirror + Si (111) double monochromator	Scan method: Stationary detector

Refinement

Refinement on Inet	Excluded region(s): none
Rp = 0.015	Profile function: pseudo-Voigt
Rwp = 0.024	27 parameters
Rexp = 0.038	Weighting scheme based on measured s.u.'s
RBragg = 0.007
χ^2 = 0.384	Background function: Legendre polynomial
7360 data points	Preferred orientation correction: March-Dollase function, axis (100)

Special details

Experimental. Japan Synchrotron Radiation Research Institute (SPring-8) 1–1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679–5198 Japan

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ge1	0.50000	0.50000	0.50000	0.0316 (8)*	0.3905 (23)
Bi1	0.50000	0.50000	0.50000	0.03157*	0.3905
Te1	0.00000	0.00000	0.00000	0.0191 (6)*

(stable_87K)

Crystal data

Ge2Bi2Te5	Dx = 7.28 Mg m^−3
Mr = 1201.04	Synchrotron, radiation radiation, λ = 0.42182 Å
Trigonal, P3m1	µ = 12.03 mm^−1
a = 4.28072 (12) Å	T = 87 K
c = 17.2651 (6) Å	cylinder, 3.0 × 0.1 mm
V = 273.99 (1) Å^3	Specimen preparation: Prepared at 300 K and 0.0002 kPa, cooled at 0 K min^−1
Z = 1

Data collection

Debye-Scherrer camera diffractometer	Specimen mounting: sealed quartz capillary tube
Radiation source: synchrotron	Data collection mode: transmission
Vertical focusing mirror + Si (111) double monochromator	Scan method: Stationary detector

Refinement

Refinement on Inet	Excluded region(s): none
Rp = 0.018	Profile function: pseudo-Voigt
Rwp = 0.028	36 parameters
Rexp = 0.038	Weighting scheme based on measured s.u.'s
RBragg = 0.016
χ^2 = 0.548	Background function: Legendre polynomial
7360 data points	Preferred orientation correction: March-Dollase function, axis (103)

Special details

Experimental. Japan Synchrotron Radiation Research Institute (SPring-8) 1–1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679–5198 Japan

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Te1	0.00000	0.00000	0.00000	0.0019 (14)*
Ge2	0.66667	0.33333	0.1069 (3)	0.0179 (10)*	0.6379 (70)
Bi2	0.66667	0.33333	0.10692	0.01786*	0.3621
Te3	0.33333	0.66667	0.2031 (2)	0.0076 (10)*
Ge4	0.00000	0.00000	0.32630	0.0168 (8)*	0.3621
Bi4	0.00000	0.00000	0.32630 (17)	0.01676*	0.6379
Te5	0.66667	0.33333	0.4212 (2)	0.0106 (11)*

(stable_293K)

Crystal data

Ge2Bi2Te5	Dx = 7.17 Mg m^−3
Mr = 1201.04	Synchrotron, radiation radiation, λ = 0.42206 Å
Trigonal, P3m1	µ = 11.85 mm^−1
a = 4.30040 (13) Å	T = 293 K
c = 17.3659 (6) Å	cylinder, 3.0 × 0.1 mm
V = 278.13 (2) Å^3	Specimen preparation: Prepared at 300 K and 0.0002 kPa, cooled at 0 K min^−1
Z = 1

Data collection

Debye-Scherrer camera diffractometer	Specimen mounting: sealed quartz capillary tube
Radiation source: synchrotron	Data collection mode: transmission
Vertical focusing mirror + Si (111) double monochromator	Scan method: Stationary detector

Refinement

Refinement on Inet	Excluded region(s): none
Rp = 0.021	Profile function: pseudo-Voigt
Rwp = 0.035	36 parameters
Rexp = 0.021	Weighting scheme based on measured s.u.'s
RBragg = 0.021
χ^2 = 2.993	Background function: Legendre polynomial
7360 data points	Preferred orientation correction: March-Dollase function, axis (001)

Special details

Experimental. Japan Synchrotron Radiation Research Institute (SPring-8) 1–1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679–5198 Japan

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Te1	0.00000	0.00000	0.00000	0.015 (2)*
Ge2	0.66667	0.33333	0.1063 (4)	0.0274 (13)*	0.6440 (85)
Bi2	0.66667	0.33333	0.10634	0.02744*	0.3560
Te3	0.33333	0.66667	0.2042 (3)	0.0143 (14)*
Ge4	0.00000	0.00000	0.32762	0.0263 (10)*	0.3560
Bi4	0.00000	0.00000	0.3276 (2)	0.02631*	0.6440
Te5	0.66667	0.33333	0.4205 (3)	0.0240 (17)*