Crystal structure and phase transition of thermoelectric SnSe

Tin selenide-based functional materials are extensively studied in the field of optoelectronic, photovoltaic and thermoelectric devices. Specifically, SnSe has been reported to have an ultrahigh thermoelectric figure of merit of 2.6 ± 0.3 in the high-temperature phase. Here we report the evolution of lattice constants, fractional coordinates, site occupancy factors and atomic displacement factors with temperature by means of high-resolution synchrotron powder X-ray diffraction measured from 100 to 855 K. The structure is shown to be cation defective with a Sn content of 0.982 (4). The anisotropy of the thermal parameters of Sn becomes more pronounced approaching the high-temperature phase transition (~ 810 K). Anharmonic Gram-Charlier parameters have been refined, but data from single-crystal diffraction appear to be needed to firmly quantify anharmonic features. Based on modelling of the atomic displacement parameters the Debye temperature is found to be 175 (4) K. Conflicting reports concerning the different coordinate system settings in the low-temperature and high-temperature phases are discussed. It is also shown that the high-temperature Cmcm phase is not pseudo-tetragonal as commonly assumed.

Computing details

For all compounds, program(s) used to refine structure: Jana2006, (Petricek,2014).

(100)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.176 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.44220 (9) Å	µ = 11.31 mm^−1
b = 4.13054 (4) Å	T = 100 K
c = 4.44900 (5) Å	metallic_grey
V = 210.27 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.38°, 2θmax = 62.2°, 2θstep = 0.01°

Refinement

Rp = 0.015	32 parameters
Rwp = 0.022	0 restraints
Rexp = 0.010	0 constraints
R(F) = 0.012	Weighting scheme based on measured s.u.'s
7800 data points	(Δ/σ)max = 0.035
Excluded region(s): from 0.01 to 4.370, from 62.21 to 78.078	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11797 (3)	0.25	0.10576 (7)	0.00474 (11)	0.9816
Se	0.85523 (4)	0.25	0.48229 (9)	0.00499 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.00419 (16)	0.0047 (2)	0.0053 (2)	0	−0.00112 (18)	0
Se	0.0052 (2)	0.0048 (3)	0.0050 (3)	0	−0.0004 (2)	0

Geometric parameters (Å, º)

Sn—Se^i	2.743	Sn—Se^iv	3.442
Sn—Se^ii	2.778	Sn—Sn^v	3.527
Sn—Se^iii	3.347	Sn—Se^vi	4.090
Se^i—Sn—Se^ii	89.140	Se^ii—Sn—Se^iii	92.685
Se^i—Sn—Se^iii	78.329	Se^i—Sn—Se^iv	159.083
Se^vii—Sn—Se^iii	76.195	Se^i—Sn—Sn^v	136.012
Se^viii—Sn—Se^ii	96.042

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(200)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.155 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.46438 (10) Å	µ = 11.27 mm^−1
b = 4.13865 (4) Å	T = 200 K
c = 4.44651 (6) Å	metallic_grey
V = 210.97 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 3.41°, 2θmax = 54.73°, 2θstep = 0.01°

Refinement

Rp = 0.016	32 parameters
Rwp = 0.023	0 restraints
Rexp = 0.010	0 constraints
R(F) = 0.013	Weighting scheme based on measured s.u.'s
7800 data points	(Δ/σ)max = 0.013
Excluded region(s): from 0.01 to 3.400, from 54.74 to 78.078	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11818 (3)	0.25	0.10454 (8)	0.00911 (14)	0.9816
Se	0.85513 (4)	0.25	0.48226 (10)	0.00852 (19)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0084 (2)	0.0087 (3)	0.0102 (3)	0	−0.0025 (2)	0
Se	0.0091 (3)	0.0080 (3)	0.0084 (3)	0	−0.0008 (3)	0

Geometric parameters (Å, º)

Sn—Se^i	2.744	Sn—Se^iv	3.452
Sn—Se^ii	2.784	Sn—Sn^v	3.534
Sn—Se^iii	3.344	Sn—Se^vi	4.093
Se^i—Sn—Se^ii	89.086	Se^ii—Sn—Se^iii	92.574
Se^i—Sn—Se^iii	78.444	Se^i—Sn—Se^iv	158.972
Se^vii—Sn—Se^iii	76.454	Se^i—Sn—Sn^v	136.232
Se^viii—Sn—Se^ii	96.020

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(275)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.134 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.48933 (12) Å	µ = 11.23 mm^−1
b = 4.14894 (5) Å	T = 275 K
c = 4.44118 (7) Å	metallic_grey
V = 211.71 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 53.18°, 2θstep = 0.01°

Refinement

Rp = 0.017	32 parameters
Rwp = 0.023	0 restraints
Rexp = 0.009	0 constraints
R(F) = 0.021	Weighting scheme based on measured s.u.'s
7801 data points	(Δ/σ)max = 0.024
Excluded region(s): from 0.01 to 4.010, from 53.19 to 78.088	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11846 (3)	0.25	0.10274 (9)	0.01406 (17)	0.9816
Se	0.85505 (4)	0.25	0.48208 (11)	0.0122 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0132 (3)	0.0129 (3)	0.0161 (3)	0	−0.0040 (3)	0
Se	0.0128 (3)	0.0123 (4)	0.0116 (4)	0	−0.0015 (3)	0

Geometric parameters (Å, º)

Sn—Se^i	2.744	Sn—Se^iv	3.464
Sn—Se^ii	2.792	Sn—Sn^v	3.542
Sn—Se^iii	3.338	Sn—Se^vi	4.094
Se^i—Sn—Se^ii	89.009	Se^ii—Sn—Se^iii	92.417
Se^i—Sn—Se^iii	78.632	Se^i—Sn—Se^iv	158.786
Se^vii—Sn—Se^iii	76.848	Se^i—Sn—Sn^v	136.541
Se^viii—Sn—Se^ii	95.971

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(300)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.127 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.49417 (12) Å	µ = 11.22 mm^−1
b = 4.15096 (5) Å	T = 300 K
c = 4.44175 (7) Å	metallic_grey
V = 211.92 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 3.31°, 2θmax = 48.15°, 2θstep = 0.01°

Refinement

Rp = 0.016	32 parameters
Rwp = 0.022	0 restraints
Rexp = 0.014	0 constraints
R(F) = 0.018	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.016
Excluded region(s): from 0.01 to 3.300, from 48.16 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11849 (4)	0.25	0.10297 (9)	0.01313 (18)	0.9816
Se	0.85523 (5)	0.25	0.48204 (11)	0.0115 (2)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0125 (3)	0.0129 (3)	0.0140 (3)	0	−0.0034 (3)	0
Se	0.0120 (4)	0.0116 (4)	0.0111 (4)	0	−0.0013 (3)	0

Geometric parameters (Å, º)

Sn—Se^i	2.747	Sn—Se^iv	3.463
Sn—Se^ii	2.792	Sn—Sn^v	3.545
Sn—Se^iii	3.339	Sn—Se^vi	4.094
Se^i—Sn—Se^ii	89.059	Se^ii—Sn—Se^iii	92.402
Se^i—Sn—Se^iii	78.664	Se^i—Sn—Se^iv	158.808
Se^vii—Sn—Se^iii	76.856	Se^i—Sn—Sn^v	136.527
Se^viii—Sn—Se^ii	96.028

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(370)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.111 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.51746 (14) Å	µ = 11.19 mm^−1
b = 4.16192 (6) Å	T = 370 K
c = 4.43267 (8) Å	metallic_grey
V = 212.48 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 3.89°, 2θmax = 38.28°, 2θstep = 0.01°

Refinement

Rp = 0.018	32 parameters
Rwp = 0.024	0 restraints
Rexp = 0.009	0 constraints
R(F) = 0.015	Weighting scheme based on measured s.u.'s
7801 data points	(Δ/σ)max = 0.017
Excluded region(s): from 0.01 to 3.880, from 38.29 to 78.088	Background function: 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11879 (4)	0.25	0.10015 (10)	0.0201 (2)	0.9816
Se	0.85505 (5)	0.25	0.48222 (13)	0.0165 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0197 (4)	0.0189 (4)	0.0218 (4)	0	−0.0055 (4)	0
Se	0.0172 (5)	0.0160 (5)	0.0162 (5)	0	−0.0023 (4)	0

Geometric parameters (Å, º)

Sn—Se^i	2.745	Sn—Se^iv	3.478
Sn—Se^ii	2.801	Sn—Sn^v	3.551
Sn—Se^iii	3.329	Sn—Se^vi	4.090
Se^i—Sn—Se^ii	88.928	Se^ii—Sn—Se^iii	92.198
Se^i—Sn—Se^iii	78.884	Se^i—Sn—Se^iv	158.501
Se^vii—Sn—Se^iii	77.368	Se^i—Sn—Sn^v	136.936
Se^viii—Sn—Se^ii	95.943

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(380)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.107 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.51965 (14) Å	µ = 11.18 mm^−1
b = 4.16265 (6) Å	T = 380 K
c = 4.43427 (8) Å	metallic_grey
V = 212.63 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 38.28°, 2θstep = 0.01°

Refinement

Rp = 0.017	32 parameters
Rwp = 0.022	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.017	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.015
Excluded region(s): from 0.01 to 4.010, from 38.29 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11883 (4)	0.25	0.10051 (10)	0.0186 (2)	0.9816
Se	0.85524 (5)	0.25	0.48217 (12)	0.0150 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0183 (3)	0.0183 (4)	0.0192 (4)	0	−0.0048 (3)	0
Se	0.0153 (4)	0.0149 (5)	0.0149 (5)	0	−0.0016 (4)	0

Geometric parameters (Å, º)

Sn—Se^i	2.748	Sn—Se^iv	3.476
Sn—Se^ii	2.801	Sn—Sn^v	3.553
Sn—Se^iii	3.331	Sn—Se^vi	4.091
Se^i—Sn—Se^ii	88.994	Se^ii—Sn—Se^iii	92.212
Se^i—Sn—Se^iii	78.910	Se^i—Sn—Se^iv	158.533
Se^vii—Sn—Se^iii	77.335	Se^i—Sn—Sn^v	136.908
Se^viii—Sn—Se^ii	95.986

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(465)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.088 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.54547 (15) Å	µ = 11.14 mm^−1
b = 4.17619 (6) Å	T = 465 K
c = 4.42402 (9) Å	metallic_grey
V = 213.31 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 38.28°, 2θstep = 0.01°

Refinement

Rp = 0.017	32 parameters
Rwp = 0.023	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.024	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.020
Excluded region(s): from 0.01 to 4.010, from 38.29 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11923 (4)	0.25	0.09733 (11)	0.0237 (2)	0.9816
Se	0.85523 (6)	0.25	0.48242 (13)	0.0185 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0239 (4)	0.0229 (5)	0.0241 (4)	0	−0.0058 (4)	0
Se	0.0183 (5)	0.0190 (5)	0.0184 (5)	0	−0.0024 (4)	0

Geometric parameters (Å, º)

Sn—Se^i	2.748	Sn—Se^iv	3.492
Sn—Se^ii	2.811	Sn—Sn^v	3.561
Sn—Se^iii	3.320	Sn—Se^vi	4.085
Se^i—Sn—Se^ii	88.906	Se^ii—Sn—Se^iii	91.973
Se^i—Sn—Se^iii	79.208	Se^i—Sn—Se^iv	158.175
Se^vii—Sn—Se^iii	77.932	Se^i—Sn—Sn^v	137.362
Se^viii—Sn—Se^ii	95.930

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(560)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.063 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.57949 (14) Å	µ = 11.10 mm^−1
b = 4.19611 (5) Å	T = 560 K
c = 4.40769 (8) Å	metallic_grey
V = 214.16 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 37.82°, 2θstep = 0.01°

Refinement

Rp = 0.017	32 parameters
Rwp = 0.022	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.028	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.035
Excluded region(s): from 0.01 to 4.010, from 37.83 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.11982 (5)	0.25	0.09182 (11)	0.0301 (3)	0.9816
Se	0.85529 (6)	0.25	0.48266 (13)	0.0233 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0300 (4)	0.0291 (5)	0.0313 (4)	0	−0.0079 (4)	0
Se	0.0227 (5)	0.0241 (5)	0.0231 (6)	0	−0.0025 (4)	0

Geometric parameters (Å, º)

Sn—Se^i	2.746	Sn—Se^iv	3.514
Sn—Se^ii	2.829	Sn—Sn^v	3.572
Sn—Se^iii	3.301	Sn—Se^vi	4.073
Se^i—Sn—Se^ii	88.744	Se^ii—Sn—Se^iii	91.621
Se^i—Sn—Se^iii	79.723	Se^i—Sn—Se^iv	157.512
Se^vii—Sn—Se^iii	78.926	Se^i—Sn—Sn^v	138.094
Se^viii—Sn—Se^ii	95.744

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(655)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.036 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.62000 (13) Å	µ = 11.05 mm^−1
b = 4.22357 (6) Å	T = 655 K
c = 4.38333 (7) Å	metallic_grey
V = 215.13 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 37.82°, 2θstep = 0.01°

Refinement

Rp = 0.017	32 parameters
Rwp = 0.023	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.035	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.041
Excluded region(s): from 0.01 to 4.010, from 37.83 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.12084 (5)	0.25	0.08170 (12)	0.0371 (3)	0.9816
Se	0.85555 (6)	0.25	0.48400 (14)	0.0295 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0352 (5)	0.0359 (6)	0.0403 (5)	0	−0.0083 (5)	0
Se	0.0274 (6)	0.0306 (6)	0.0304 (7)	0	−0.0011 (5)	0

Geometric parameters (Å, º)

Sn—Se^i	2.742	Sn—Se^iv	3.551
Sn—Se^ii	2.856	Sn—Sn^v	3.586
Sn—Se^iii	3.269	Sn—Se^vi	4.046
Se^i—Sn—Se^ii	88.539	Se^ii—Sn—Se^iii	91.139
Se^i—Sn—Se^iii	80.612	Se^i—Sn—Se^iv	156.257
Se^vii—Sn—Se^iii	80.494	Se^i—Sn—Sn^v	139.274
Se^viii—Sn—Se^ii	95.348

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(705)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.022 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.64398 (13) Å	µ = 11.02 mm^−1
b = 4.24224 (5) Å	T = 705 K
c = 4.36522 (7) Å	metallic_grey
V = 215.63 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 34.48°, 2θstep = 0.01°

Refinement

Rp = 0.018	32 parameters
Rwp = 0.024	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.031	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.011
Excluded region(s): from 0.01 to 4.010, from 34.49 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.12148 (6)	0.25	0.07350 (13)	0.0416 (3)	0.9816
Se	0.85571 (7)	0.25	0.48517 (16)	0.0326 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0386 (5)	0.0417 (7)	0.0446 (6)	0	−0.0088 (5)	0
Se	0.0299 (6)	0.0330 (7)	0.0348 (7)	0	−0.0007 (6)	0

Geometric parameters (Å, º)

Sn—Se^i	2.739	Sn—Se^iv	3.579
Sn—Se^ii	2.878	Sn—Sn^v	3.594
Sn—Se^iii	3.243	Sn—Se^vi	4.021
Se^i—Sn—Se^ii	88.321	Se^ii—Sn—Se^iii	90.789
Se^i—Sn—Se^iii	81.266	Se^i—Sn—Se^iv	155.221
Se^vii—Sn—Se^iii	81.697	Se^i—Sn—Sn^v	140.094
Se^viii—Sn—Se^ii	94.968

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(755)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 6.007 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.67175 (14) Å	µ = 11.00 mm^−1
b = 4.26761 (6) Å	T = 755 K
c = 4.33976 (7) Å	metallic_grey
V = 216.17 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 34.48°, 2θstep = 0.01°

Refinement

Rp = 0.020	27 parameters
Rwp = 0.026	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.042	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.046
Excluded region(s): from 0.01 to 4.010, from 34.49 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.12231 (6)	0.25	0.05985 (16)	0.0475 (4)	0.9816
Se	0.85591 (7)	0.25	0.4881 (2)	0.0351 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0419 (6)	0.0498 (8)	0.0508 (7)	0	−0.0100 (7)	0
Se	0.0339 (7)	0.0331 (9)	0.0383 (9)	0	−0.0028 (7)	0

Geometric parameters (Å, º)

Sn—Se^i	2.734	Sn—Se^iv	3.622
Sn—Se^ii	2.910	Sn—Sn^v	3.602
Sn—Se^iii	3.205	Sn—Se^vi	3.978
Se^i—Sn—Se^ii	87.948	Se^ii—Sn—Se^iii	90.291
Se^i—Sn—Se^iii	82.211	Se^i—Sn—Se^iv	153.496
Se^vii—Sn—Se^iii	83.482	Se^i—Sn—Sn^v	141.203
Se^viii—Sn—Se^ii	94.334

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(805)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Pnma	Dx = 5.991 Mg m^−3
Hall symbol: -P 2ac 2n	Synchrotron,monochromatic radiation
a = 11.70577 (16) Å	µ = 10.97 mm^−1
b = 4.30722 (16) Å	T = 805 K
c = 4.29911 (16) Å	metallic_grey
V = 216.76 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 34.48°, 2θstep = 0.01°

Refinement

Rp = 0.022	32 parameters
Rwp = 0.030	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.058	Weighting scheme based on measured s.u.'s
7797 data points	(Δ/σ)max = 0.040
Excluded region(s): from 0.01 to 4.010, from 34.49 to 78.048	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0.12399 (7)	0.25	0.0192 (6)	0.0577 (9)	0.9816
Se	0.85663 (9)	0.25	0.4968 (8)	0.0396 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0479 (7)	0.062 (2)	0.0627 (16)	0	−0.0181 (19)	0
Se	0.0402 (10)	0.038 (2)	0.0406 (18)	0	0.000 (2)	0

Geometric parameters (Å, º)

Sn—Se^i	2.724	Sn—Se^iv	3.743
Sn—Se^ii	3.003	Sn—Sn^v	3.618
Sn—Se^iii	3.100	Sn—Se^vi	3.852
Se^i—Sn—Se^ii	86.677	Se^ii—Sn—Se^iii	89.547
Se^i—Sn—Se^iii	84.766	Se^i—Sn—Se^iv	148.185
Se^vii—Sn—Se^iii	88.003	Se^i—Sn—Sn^v	143.213
Se^viii—Sn—Se^ii	91.636

Symmetry codes: (i) x−1/2, −y+1/2, −z+1/2; (ii) −x+1, y+1/2, −z+1; (iii) −x+1, y+1/2, −z; (iv) x−1, y, z; (v) −x, y−1/2, −z; (vi) x−1, y, z−1; (vii) −x+1, y−1/2, −z; (viii) −x+1, y−1/2, −z+1.

(855)

Crystal data

SeSn0.9816	Z = 4
Mr = 195.50	F(000) = 332.3
Orthorhombic, Cmcm	Dx = 5.973 Mg m^−3
Hall symbol: -C 2c 2	Synchrotron,monochromatic radiation
a = 4.29978 (8) Å	µ = 10.93 mm^−1
b = 11.71878 (17) Å	T = 855 K
c = 4.31479 (8) Å	metallic_grey
V = 217.41 (1) Å^3

Data collection

BL44B2 diffractometer	Data collection mode: transmission
Specimen mounting: capillary	2θmin = 4.02°, 2θmax = 32.22°, 2θstep = 0.01°

Refinement

Rp = 0.022	28 parameters
Rwp = 0.030	0 restraints
Rexp = 0.013	0 constraints
R(F) = 0.032	Weighting scheme based on measured s.u.'s
7798 data points	(Δ/σ)max = 0.013
Excluded region(s): from 0.01 to 4.010, from 32.23 to 78.058	Background function: Manual background combined with 8 Chebyshev polynoms
Profile function: Pseudo-Voigt	Preferred orientation correction: none

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Sn	0	0.12424 (7)	0.25	0.0634 (6)	0.9816
Se	0.5	0.85654 (8)	0.25	0.0422 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Sn	0.0804 (13)	0.0492 (8)	0.0606 (11)	0	0	0
Se	0.0490 (14)	0.0400 (10)	0.0375 (13)	0	0	0

Geometric parameters (Å, º)

Sn—Se^i	2.722	Sn—Se^iv	3.803
Sn—Se^ii	3.054	Sn—Sn^v	3.624
Sn—Se^iii	3.054	Sn—Se^vi	3.803
Se^i—Sn—Se^ii	85.771	Se^ii—Sn—Se^iii	89.490
Se^i—Sn—Se^iii	85.771	Se^i—Sn—Se^iv	145.577
Se^vii—Sn—Se^iii	89.887	Se^i—Sn—Sn^v	143.465
Se^viii—Sn—Se^ii	89.887

Symmetry codes: (i) −x+1/2, y−1/2, −z+1/2; (ii) −x+1, −y+1, z+1/2; (iii) −x, −y+1, z+1/2; (iv) x, y−1, z; (v) −x, −y, z−1/2; (vi) x−1, y−1, z; (vii) −x, −y+1, z−1/2; (viii) −x+1, −y+1, z−1/2.