Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270103024776/sq1031sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270103024776/sq1031Isup2.hkl |
A single-crystal was extracted from an arc-melted Sm40Ga20Sn40 ingot, annealed at 870 K for one month. To investigate an evolution of the structure as a function of the Ga content, ten alloys with nominal compositions Sm37.5Ga7–34Sn55.5–28.5 were additionally prepared, with each sample 2 g, arc-melting with less than 0.5% weight losses and annealing at 870 K for one month. The X-ray powder diffraction patterns were recorded at room temperature with a Bruker D8 Advance diffractometer (Cu Kα1 radiation, 2θmin/max = 20–120°, increment in 2θ = 0.0144°). One scale factor, ten profile and seven structural parameters were refined for each composition by the Rietveld method, using the FULLPROF2002 program package (Rodriguez-Carvajal, 1990).
The atomic positions were standardized with the STRUCTURE TIDY program (Gelato & Parthé, 1987). In the final difference Fourier map, all peaks greater than 1 e Å−3 (maximum 2.47 e Å−3) are located within 1 Å of the atomic positions.
Data collection: EXPOSE in IPDS Software (Stoe & Cie, 1999); cell refinement: CELL in IPDS Software; data reduction: INTEGRATE in IPDS Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1993); software used to prepare material for publication: SHELXL97.
Ga1.89Sm3Sn3.11 | Dx = 7.911 Mg m−3 |
Mr = 951.80 | Mo Kα radiation, λ = 0.71069 Å |
Orthorhombic, Cmcm | Cell parameters from 1823 reflections |
a = 9.9680 (13) Å | θ = 4.0–30.0° |
b = 7.9720 (17) Å | µ = 37.38 mm−1 |
c = 10.056 (2) Å | T = 293 K |
V = 799.1 (3) Å3 | Plate-like, metallic light grey |
Z = 4 | 0.07 × 0.06 × 0.03 mm |
F(000) = 1600 |
Stoe IPDS diffractometer | 640 independent reflections |
Radiation source: fine-focus sealed tube | 556 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.060 |
ϕ oscillation scans | θmax = 30.0°, θmin = 3.9° |
Absorption correction: analytical (X-RED; Stoe & Cie, 1999) | h = −13→14 |
Tmin = 0.155, Tmax = 0.414 | k = −11→10 |
3252 measured reflections | l = −14→14 |
Refinement on F2 | 0 restraints |
Least-squares matrix: full | Primary atom site location: structure-invariant direct methods |
R[F2 > 2σ(F2)] = 0.024 | Secondary atom site location: difference Fourier map |
wR(F2) = 0.053 | w = 1/[σ2(Fo2) + (0.031P)2] where P = (Fo2 + 2Fc2)/3 |
S = 0.99 | (Δ/σ)max < 0.001 |
640 reflections | Δρmax = 2.47 e Å−3 |
29 parameters | Δρmin = −2.61 e Å−3 |
Ga1.89Sm3Sn3.11 | V = 799.1 (3) Å3 |
Mr = 951.80 | Z = 4 |
Orthorhombic, Cmcm | Mo Kα radiation |
a = 9.9680 (13) Å | µ = 37.38 mm−1 |
b = 7.9720 (17) Å | T = 293 K |
c = 10.056 (2) Å | 0.07 × 0.06 × 0.03 mm |
Stoe IPDS diffractometer | 640 independent reflections |
Absorption correction: analytical (X-RED; Stoe & Cie, 1999) | 556 reflections with I > 2σ(I) |
Tmin = 0.155, Tmax = 0.414 | Rint = 0.060 |
3252 measured reflections |
R[F2 > 2σ(F2)] = 0.024 | 29 parameters |
wR(F2) = 0.053 | 0 restraints |
S = 0.99 | Δρmax = 2.47 e Å−3 |
640 reflections | Δρmin = −2.61 e Å−3 |
Experimental. The compositions of the alloys were checked during the preparation. It was mentioned in the Experimental section that weight losses during preparation were insignificant (less than 0.5% for 2 g samples). It was therefore considered that the alloys' compositions correspond to the nominal compositions. Weight losses during the sample preparation were less than the precision of the composition refinement from the X-ray powder data. The fact that refined compositions correspond to the nominal compositions of the samples confirms the accuracy of our results. |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
Sn1 | 0.20466 (6) | 0.28795 (8) | 0.2500 | 0.0104 (2) | 0.930 (12) |
Ga1 | 0.20466 (6) | 0.28795 (8) | 0.2500 | 0.0104 (2) | 0.070 (12) |
Sn2 | 0.0000 | 0.31416 (11) | 0.04613 (8) | 0.0120 (3) | 0.356 (12) |
Ga2 | 0.0000 | 0.31416 (11) | 0.04613 (8) | 0.0120 (3) | 0.644 (12) |
Sm1 | 0.20025 (4) | 0.0000 | 0.0000 | 0.00926 (14) | |
Sn3 | 0.0000 | 0.02592 (13) | 0.2500 | 0.0091 (4) | 0.535 (17) |
Ga3 | 0.0000 | 0.02592 (13) | 0.2500 | 0.0091 (4) | 0.465 (17) |
Sm2 | 0.0000 | 0.63989 (8) | 0.2500 | 0.00969 (15) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Sn1 | 0.0075 (3) | 0.0131 (4) | 0.0108 (3) | −0.0020 (2) | 0.000 | 0.000 |
Ga1 | 0.0075 (3) | 0.0131 (4) | 0.0108 (3) | −0.0020 (2) | 0.000 | 0.000 |
Sn2 | 0.0084 (4) | 0.0161 (5) | 0.0117 (4) | 0.000 | 0.000 | −0.0014 (3) |
Ga2 | 0.0084 (4) | 0.0161 (5) | 0.0117 (4) | 0.000 | 0.000 | −0.0014 (3) |
Sm1 | 0.0064 (2) | 0.0098 (2) | 0.0116 (2) | 0.000 | 0.000 | −0.00072 (15) |
Sn3 | 0.0074 (5) | 0.0092 (6) | 0.0107 (5) | 0.000 | 0.000 | 0.000 |
Ga3 | 0.0074 (5) | 0.0092 (6) | 0.0107 (5) | 0.000 | 0.000 | 0.000 |
Sm2 | 0.0061 (3) | 0.0100 (3) | 0.0130 (3) | 0.000 | 0.000 | 0.000 |
Sn1—Sn2 | 2.8997 (8) | Sm1—Sn1iv | 3.1743 (6) |
Sn1—Ga2i | 2.8997 (8) | Sm1—Ga3vii | 3.2167 (5) |
Sn1—Sn2i | 2.8997 (8) | Sm1—Sn3vii | 3.2167 (5) |
Sn1—Ga2i | 2.8997 (8) | Sm1—Ga3 | 3.2167 (5) |
Sn1—Sn3 | 2.9198 (10) | Sm1—Sn3 | 3.2167 (5) |
Sn1—Ga3 | 2.9198 (10) | Sm1—Ga2vii | 3.2360 (9) |
Sn1—Sm2ii | 3.1718 (7) | Sm1—Sn2vii | 3.2360 (9) |
Sn1—Sm1iii | 3.1743 (6) | Sn3—Ga1v | 2.9198 (10) |
Sn1—Sm1iv | 3.1743 (6) | Sn3—Sn1v | 2.9198 (10) |
Sn1—Sm1 | 3.4046 (7) | Sn3—Sm2ix | 3.0775 (14) |
Sn1—Sm1i | 3.4046 (7) | Sn3—Ga2i | 3.0794 (12) |
Sn1—Sm2 | 3.4689 (10) | Sn3—Sn2i | 3.0794 (12) |
Sn2—Ga1v | 2.8997 (8) | Sn3—Sm1vii | 3.2167 (5) |
Sn2—Sn1v | 2.8997 (8) | Sn3—Sm1i | 3.2167 (5) |
Sn2—Sm2vi | 3.0003 (10) | Sn3—Sm1x | 3.2167 (5) |
Sn2—Sn3 | 3.0794 (12) | Sm2—Ga2xi | 3.0003 (10) |
Sn2—Ga3 | 3.0794 (12) | Sm2—Sn2xi | 3.0003 (10) |
Sn2—Ga2vi | 3.1049 (18) | Sm2—Ga2vi | 3.0003 (10) |
Sn2—Sn2vi | 3.1049 (18) | Sm2—Sn2vi | 3.0003 (10) |
Sn2—Sm1vii | 3.2360 (9) | Sm2—Ga3xii | 3.0775 (14) |
Sn2—Sm1 | 3.2360 (9) | Sm2—Sn3xii | 3.0775 (14) |
Sn2—Sm2 | 3.3085 (11) | Sm2—Ga1xiii | 3.1718 (7) |
Sm1—Ga1viii | 3.1743 (6) | Sm2—Sn1xiii | 3.1718 (7) |
Sm1—Sn1viii | 3.1743 (6) | Sm2—Sn1xiv | 3.1718 (7) |
Sm1—Ga1iv | 3.1743 (6) | Sm2—Ga1xiv | 3.1718 (7) |
Sn2—Sn1—Ga2i | 89.98 (3) | Ga1viii—Sm1—Sn2vii | 83.43 (2) |
Sn2—Sn1—Sn2i | 89.98 (3) | Sn1viii—Sm1—Sn2vii | 83.43 (2) |
Ga2i—Sn1—Sn2i | 0.00 (4) | Ga1iv—Sm1—Sn2vii | 118.870 (19) |
Sn2—Sn1—Sn3 | 63.90 (2) | Sn1iv—Sm1—Sn2vii | 118.870 (19) |
Ga2i—Sn1—Sn3 | 63.90 (2) | Ga3vii—Sm1—Sn2vii | 57.01 (2) |
Sn2i—Sn1—Sn3 | 63.90 (2) | Sn3vii—Sm1—Sn2vii | 57.01 (2) |
Sn2—Sn1—Sm2ii | 132.829 (19) | Sn3—Sm1—Sn2vii | 77.23 (2) |
Ga2i—Sn1—Sm2ii | 132.829 (19) | Ga2vii—Sm1—Sn2vii | 0.00 (3) |
Sn2i—Sn1—Sm2ii | 132.829 (19) | Ga1viii—Sm1—Sn2 | 118.870 (19) |
Sn3—Sn1—Sm2ii | 112.47 (3) | Sn1viii—Sm1—Sn2 | 118.870 (19) |
Sn2—Sn1—Sm1iii | 137.02 (3) | Ga1iv—Sm1—Sn2 | 83.43 (2) |
Ga2i—Sn1—Sm1iii | 67.156 (19) | Sn1iv—Sm1—Sn2 | 83.43 (2) |
Sn2i—Sn1—Sm1iii | 67.156 (19) | Ga3vii—Sm1—Sn2 | 77.23 (2) |
Sn3—Sn1—Sm1iii | 126.131 (13) | Sn3vii—Sm1—Sn2 | 77.23 (2) |
Sm2ii—Sn1—Sm1iii | 85.469 (17) | Sn3—Sm1—Sn2 | 57.01 (2) |
Sn2—Sn1—Sm1iv | 67.156 (19) | Ga2vii—Sm1—Sn2 | 103.83 (3) |
Ga2i—Sn1—Sm1iv | 137.02 (3) | Sn2vii—Sm1—Sn2 | 103.83 (3) |
Sn2i—Sn1—Sm1iv | 137.02 (3) | Sn1—Sn3—Ga1v | 88.64 (4) |
Sn3—Sn1—Sm1iv | 126.131 (13) | Sn1—Sn3—Sn1v | 88.64 (4) |
Sm2ii—Sn1—Sm1iv | 85.469 (17) | Ga1v—Sn3—Sn1v | 0.00 (2) |
Sm1iii—Sn1—Sm1iv | 104.74 (2) | Sn1—Sn3—Sm2ix | 135.68 (2) |
Sn2—Sn1—Sm1 | 61.15 (2) | Ga1v—Sn3—Sm2ix | 135.68 (2) |
Ga2i—Sn1—Sm1 | 124.16 (3) | Sn1v—Sn3—Sm2ix | 135.68 (2) |
Sn2i—Sn1—Sm1 | 124.16 (3) | Sn1—Sn3—Ga2i | 57.74 (2) |
Sn3—Sn1—Sm1 | 60.569 (16) | Ga1v—Sn3—Ga2i | 57.74 (2) |
Sm2ii—Sn1—Sm1 | 76.177 (16) | Sn1v—Sn3—Ga2i | 57.74 (2) |
Sm1iii—Sn1—Sm1 | 161.39 (2) | Sm2ix—Sn3—Ga2i | 138.26 (2) |
Sm1iv—Sn1—Sm1 | 77.180 (16) | Sn1—Sn3—Sn2i | 57.74 (2) |
Sn2—Sn1—Sm1i | 124.16 (3) | Ga1v—Sn3—Sn2i | 57.74 (2) |
Ga2i—Sn1—Sm1i | 61.15 (2) | Sn1v—Sn3—Sn2i | 57.74 (2) |
Sn2i—Sn1—Sm1i | 61.15 (2) | Sm2ix—Sn3—Sn2i | 138.26 (2) |
Sn3—Sn1—Sm1i | 60.569 (16) | Ga2i—Sn3—Sn2i | 0.00 (3) |
Sm2ii—Sn1—Sm1i | 76.177 (16) | Sn1—Sn3—Sn2 | 57.74 (2) |
Sm1iii—Sn1—Sm1i | 77.180 (16) | Ga1v—Sn3—Sn2 | 57.74 (2) |
Sm1iv—Sn1—Sm1i | 161.39 (2) | Sn1v—Sn3—Sn2 | 57.74 (2) |
Sm1—Sn1—Sm1i | 95.19 (2) | Sm2ix—Sn3—Sn2 | 138.26 (2) |
Sn2—Sn1—Sm2 | 61.84 (2) | Ga2i—Sn3—Sn2 | 83.48 (4) |
Ga2i—Sn1—Sm2 | 61.84 (2) | Sn2i—Sn3—Sn2 | 83.48 (4) |
Sn2i—Sn1—Sm2 | 61.84 (2) | Sn1—Sn3—Sm1vii | 118.65 (2) |
Sn3—Sn1—Sm2 | 99.66 (3) | Ga1v—Sn3—Sm1vii | 67.195 (12) |
Sm2ii—Sn1—Sm2 | 147.87 (3) | Sn1v—Sn3—Sm1vii | 67.195 (12) |
Sm1iii—Sn1—Sm2 | 75.220 (17) | Sm2ix—Sn3—Sm1vii | 86.316 (18) |
Sm1iv—Sn1—Sm2 | 75.220 (17) | Ga2i—Sn3—Sm1vii | 124.63 (3) |
Sm1—Sn1—Sm2 | 122.530 (15) | Sn2i—Sn3—Sm1vii | 124.63 (3) |
Sm1i—Sn1—Sm2 | 122.530 (15) | Sn2—Sn3—Sm1vii | 61.812 (16) |
Sn1—Sn2—Ga1v | 89.42 (3) | Sn1—Sn3—Sm1i | 67.195 (12) |
Sn1—Sn2—Sn1v | 89.42 (3) | Ga1v—Sn3—Sm1i | 118.65 (2) |
Ga1v—Sn2—Sn1v | 0.00 (3) | Sn1v—Sn3—Sm1i | 118.65 (2) |
Sn1—Sn2—Sm2vi | 135.277 (15) | Sm2ix—Sn3—Sm1i | 86.316 (18) |
Ga1v—Sn2—Sm2vi | 135.277 (15) | Ga2i—Sn3—Sm1i | 61.812 (16) |
Sn1v—Sn2—Sm2vi | 135.277 (15) | Sn2i—Sn3—Sm1i | 61.812 (16) |
Sn1—Sn2—Sn3 | 58.37 (2) | Sn2—Sn3—Sm1i | 124.63 (3) |
Ga1v—Sn2—Sn3 | 58.37 (2) | Sm1vii—Sn3—Sm1i | 172.63 (4) |
Sn1v—Sn2—Sn3 | 58.37 (2) | Sn1—Sn3—Sm1x | 118.65 (2) |
Sm2vi—Sn2—Sn3 | 138.75 (4) | Ga1v—Sn3—Sm1x | 67.195 (12) |
Sn1—Sn2—Ga2vi | 106.26 (3) | Sn1v—Sn3—Sm1x | 67.195 (12) |
Ga1v—Sn2—Ga2vi | 106.26 (3) | Sm2ix—Sn3—Sm1x | 86.316 (18) |
Sn1v—Sn2—Ga2vi | 106.26 (3) | Ga2i—Sn3—Sm1x | 61.812 (16) |
Sm2vi—Sn2—Ga2vi | 65.60 (3) | Sn2i—Sn3—Sm1x | 61.812 (16) |
Sn3—Sn2—Ga2vi | 155.65 (4) | Sn2—Sn3—Sm1x | 124.63 (3) |
Sn1—Sn2—Sn2vi | 106.26 (3) | Sm1vii—Sn3—Sm1x | 102.804 (18) |
Ga1v—Sn2—Sn2vi | 106.26 (3) | Sm1i—Sn3—Sm1x | 76.710 (18) |
Sn1v—Sn2—Sn2vi | 106.26 (3) | Ga2xi—Sm2—Sn2xi | 0.00 (3) |
Sm2vi—Sn2—Sn2vi | 65.60 (3) | Ga2xi—Sm2—Ga2vi | 165.97 (4) |
Sn3—Sn2—Sn2vi | 155.65 (4) | Sn2xi—Sm2—Ga2vi | 165.97 (4) |
Ga2vi—Sn2—Sn2vi | 0.00 (3) | Ga2xi—Sm2—Sn2vi | 165.97 (4) |
Sn1—Sn2—Sm1vii | 118.65 (3) | Sn2xi—Sm2—Sn2vi | 165.97 (4) |
Ga1v—Sn2—Sm1vii | 67.147 (18) | Ga2vi—Sm2—Sn2vi | 0.00 (3) |
Sn1v—Sn2—Sm1vii | 67.147 (18) | Ga2xi—Sm2—Ga3xii | 82.99 (2) |
Sm2vi—Sn2—Sm1vii | 87.26 (2) | Sn2xi—Sm2—Ga3xii | 82.99 (2) |
Sn3—Sn2—Sm1vii | 61.18 (2) | Ga2vi—Sm2—Ga3xii | 82.99 (2) |
Ga2vi—Sn2—Sm1vii | 134.09 (2) | Sn2vi—Sm2—Ga3xii | 82.99 (2) |
Sn2vi—Sn2—Sm1vii | 134.09 (2) | Ga2xi—Sm2—Sn3xii | 82.99 (2) |
Sn1—Sn2—Sm1 | 67.147 (18) | Sn2xi—Sm2—Sn3xii | 82.99 (2) |
Ga1v—Sn2—Sm1 | 118.65 (3) | Ga2vi—Sm2—Sn3xii | 82.99 (2) |
Sn1v—Sn2—Sm1 | 118.65 (3) | Sn2vi—Sm2—Sn3xii | 82.99 (2) |
Sm2vi—Sn2—Sm1 | 87.26 (2) | Ga3xii—Sm2—Sn3xii | 0.0 |
Sn3—Sn2—Sm1 | 61.18 (2) | Ga2xi—Sm2—Ga1xiii | 87.396 (9) |
Ga2vi—Sn2—Sm1 | 134.09 (2) | Sn2xi—Sm2—Ga1xiii | 87.396 (9) |
Sn2vi—Sn2—Sm1 | 134.09 (2) | Ga2vi—Sm2—Ga1xiii | 87.396 (9) |
Sm1vii—Sn2—Sm1 | 76.17 (3) | Sn2vi—Sm2—Ga1xiii | 87.396 (9) |
Sn1—Sn2—Sm2 | 67.57 (2) | Ga3xii—Sm2—Ga1xiii | 68.153 (17) |
Ga1v—Sn2—Sm2 | 67.57 (2) | Sn3xii—Sm2—Ga1xiii | 68.153 (17) |
Sn1v—Sn2—Sm2 | 67.57 (2) | Ga2xi—Sm2—Sn1xiii | 87.396 (9) |
Sm2vi—Sn2—Sm2 | 121.28 (3) | Sn2xi—Sm2—Sn1xiii | 87.396 (9) |
Sn3—Sn2—Sm2 | 99.97 (3) | Ga2vi—Sm2—Sn1xiii | 87.396 (9) |
Ga2vi—Sn2—Sm2 | 55.68 (3) | Sn2vi—Sm2—Sn1xiii | 87.396 (9) |
Sn2vi—Sn2—Sm2 | 55.68 (3) | Ga3xii—Sm2—Sn1xiii | 68.153 (17) |
Sm1vii—Sn2—Sm2 | 134.128 (18) | Sn3xii—Sm2—Sn1xiii | 68.153 (17) |
Sm1—Sn2—Sm2 | 134.128 (18) | Ga1xiii—Sm2—Sn1xiii | 0.00 (2) |
Ga1viii—Sm1—Sn1viii | 0.00 (3) | Ga2xi—Sm2—Sn1xiv | 87.396 (9) |
Ga1viii—Sm1—Ga1iv | 145.25 (3) | Sn2xi—Sm2—Sn1xiv | 87.396 (9) |
Sn1viii—Sm1—Ga1iv | 145.25 (3) | Ga2vi—Sm2—Sn1xiv | 87.396 (9) |
Ga1viii—Sm1—Sn1iv | 145.25 (3) | Sn2vi—Sm2—Sn1xiv | 87.396 (9) |
Sn1viii—Sm1—Sn1iv | 145.25 (3) | Ga3xii—Sm2—Sn1xiv | 68.153 (17) |
Ga1iv—Sm1—Sn1iv | 0.00 (3) | Sn3xii—Sm2—Sn1xiv | 68.153 (17) |
Ga1viii—Sm1—Ga3vii | 140.36 (2) | Ga1xiii—Sm2—Sn1xiv | 136.31 (3) |
Sn1viii—Sm1—Ga3vii | 140.36 (2) | Sn1xiii—Sm2—Sn1xiv | 136.31 (3) |
Ga1iv—Sm1—Ga3vii | 66.456 (18) | Ga2xi—Sm2—Ga1xiv | 87.396 (9) |
Sn1iv—Sm1—Ga3vii | 66.456 (18) | Sn2xi—Sm2—Ga1xiv | 87.396 (9) |
Ga1viii—Sm1—Sn3vii | 140.36 (2) | Ga2vi—Sm2—Ga1xiv | 87.396 (9) |
Sn1viii—Sm1—Sn3vii | 140.36 (2) | Sn2vi—Sm2—Ga1xiv | 87.396 (9) |
Ga1iv—Sm1—Sn3vii | 66.456 (18) | Ga3xii—Sm2—Ga1xiv | 68.153 (17) |
Sn1iv—Sm1—Sn3vii | 66.456 (18) | Sn3xii—Sm2—Ga1xiv | 68.153 (17) |
Ga3vii—Sm1—Sn3vii | 0.00 (4) | Ga1xiii—Sm2—Ga1xiv | 136.31 (3) |
Ga1viii—Sm1—Sn3 | 66.456 (18) | Sn1xiii—Sm2—Ga1xiv | 136.31 (3) |
Sn1viii—Sm1—Sn3 | 66.456 (18) | Sn1xiv—Sm2—Ga1xiv | 0.00 (2) |
Ga1iv—Sm1—Sn3 | 140.36 (2) | Ga2xi—Sm2—Sn2 | 135.30 (3) |
Sn1iv—Sm1—Sn3 | 140.36 (2) | Sn2xi—Sm2—Sn2 | 135.30 (3) |
Ga3vii—Sm1—Sn3 | 103.290 (18) | Ga2vi—Sm2—Sn2 | 58.72 (3) |
Sn3vii—Sm1—Sn3 | 103.290 (18) | Sn2vi—Sm2—Sn2 | 58.72 (3) |
Ga1viii—Sm1—Ga2vii | 83.43 (2) | Ga3xii—Sm2—Sn2 | 141.709 (18) |
Sn1viii—Sm1—Ga2vii | 83.43 (2) | Sn3xii—Sm2—Sn2 | 141.709 (18) |
Ga1iv—Sm1—Ga2vii | 118.870 (19) | Ga1xiii—Sm2—Sn2 | 106.982 (13) |
Sn1iv—Sm1—Ga2vii | 118.870 (19) | Sn1xiii—Sm2—Sn2 | 106.982 (13) |
Ga3vii—Sm1—Ga2vii | 57.01 (2) | Sn1xiv—Sm2—Sn2 | 106.982 (13) |
Sn3vii—Sm1—Ga2vii | 57.01 (2) | Ga1xiv—Sm2—Sn2 | 106.982 (13) |
Sn3—Sm1—Ga2vii | 77.23 (2) |
Symmetry codes: (i) x, y, −z+1/2; (ii) x+1/2, y−1/2, z; (iii) −x+1/2, −y+1/2, z+1/2; (iv) −x+1/2, −y+1/2, −z; (v) −x, y, −z+1/2; (vi) −x, −y+1, −z; (vii) −x, −y, −z; (viii) −x+1/2, y−1/2, −z+1/2; (ix) x, y−1, z; (x) −x, −y, z+1/2; (xi) −x, −y+1, z+1/2; (xii) x, y+1, z; (xiii) −x+1/2, y+1/2, −z+1/2; (xiv) x−1/2, y+1/2, z. |
Experimental details
Crystal data | |
Chemical formula | Ga1.89Sm3Sn3.11 |
Mr | 951.80 |
Crystal system, space group | Orthorhombic, Cmcm |
Temperature (K) | 293 |
a, b, c (Å) | 9.9680 (13), 7.9720 (17), 10.056 (2) |
V (Å3) | 799.1 (3) |
Z | 4 |
Radiation type | Mo Kα |
µ (mm−1) | 37.38 |
Crystal size (mm) | 0.07 × 0.06 × 0.03 |
Data collection | |
Diffractometer | Stoe IPDS diffractometer |
Absorption correction | Analytical (X-RED; Stoe & Cie, 1999) |
Tmin, Tmax | 0.155, 0.414 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3252, 640, 556 |
Rint | 0.060 |
(sin θ/λ)max (Å−1) | 0.703 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.024, 0.053, 0.99 |
No. of reflections | 640 |
No. of parameters | 29 |
Δρmax, Δρmin (e Å−3) | 2.47, −2.61 |
Computer programs: EXPOSE in IPDS Software (Stoe & Cie, 1999), CELL in IPDS Software, INTEGRATE in IPDS Software, SHELXS97 (Sheldrick, 1997), SHELXL97 (Sheldrick, 1997), ATOMS (Dowty, 1993), SHELXL97.
Sn1—Sn2 | 2.8997 (8) | Sn2—Sm1iv | 3.2360 (9) |
Sn1—Sn3 | 2.9198 (10) | Sn2—Sm2 | 3.3085 (11) |
Sn1—Sm2i | 3.1718 (7) | Sm1—Sn1v | 3.1743 (6) |
Sn1—Sm1ii | 3.1743 (6) | Sm1—Sn3 | 3.2167 (5) |
Sn1—Sm1 | 3.4046 (7) | Sm1—Sn2iv | 3.2360 (9) |
Sn1—Sm2 | 3.4689 (10) | Sn3—Sn1vi | 2.9198 (10) |
Sn2—Sm2iii | 3.0003 (10) | Sn3—Sm2vii | 3.0775 (14) |
Sn2—Sn3 | 3.0794 (12) | Sn3—Sm1viii | 3.2167 (5) |
Sn2—Ga2iii | 3.1049 (18) |
Symmetry codes: (i) x+1/2, y−1/2, z; (ii) −x+1/2, −y+1/2, z+1/2; (iii) −x, −y+1, −z; (iv) −x, −y, −z; (v) −x+1/2, y−1/2, −z+1/2; (vi) −x, y, −z+1/2; (vii) x, y−1, z; (viii) x, y, −z+1/2. |
Sn1 | 8 g | 0.20466 (6) | 0.28795 (8) | 0.2500 | 0.930 (12) |
Ga1 | 8 g | 0.20466 (6) | 0.28795 (8) | 0.2500 | 0.070 (12) |
Sn2 | 8f | 0.0000 | 0.31416 (11) | 0.04613 (8) | 0.356 (12) |
Ga2 | 8f | 0.0000 | 0.31416 (11) | 0.04613 (8) | 0.644 (12) |
Sm1 | 8 e | 0.20025 (4) | 0.0000 | 0.0000 | 1 |
Sn3 | 4c | 0.0000 | 0.02592 (13) | 0.2500 | 0.535 (17) |
Ga3 | 4c | 0.0000 | 0.02592 (13) | 0.2500 | 0.465 (17) |
Sm2 | 4c | 0.0000 | 0.63989 (8) | 0.2500 | 1 |
Ga (at.%) | a (Å) | b (Å) | c (Å) | V (Å3) |
10 | 9.97522 (18) | 8.02642 (16) | 10.23304 (19) | 819.31 (3) |
13 | 9.96543 (17) | 8.01286 (16) | 10.1906 (2) | 813.73 (3) |
16 | 9.95661 (19) | 7.99150 (18) | 10.1297 (2) | 806.00 (4) |
19 | 9.9488 (2) | 7.9686 (2) | 10.0739 (3) | 798.64 (4) |
22 | 9.9402 (2) | 7.9490 (2) | 10.0367 (3) | 793.04 (4) |
25 | 9.9268 (3) | 7.9255 (2) | 9.9945 (3) | 786.32 (4) |
28 | 9.91021 (13) | 7.89376 (11) | 9.94854 (16) | 778.26 (2) |
31 | 9.89433 (18) | 7.87246 (16) | 9.91703 (19) | 772.46 (2) |
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Among numerous intermetallic compounds crystallizing with a Pu3Pd5 structure type (Cromer, 1976), only one ternary compound, Er3Ga2Ge3, has been reported to date (Welter & Venturini, 1999). In spite of the negligible contrast between Ga and Ge atoms in their nonresonant X-ray diffraction experiment, Welter & Venturini assumed a partially ordered Ga/Ge distribution, though admitting that `the evolution of the structure as a function of the Ga content is not well understood'. We present here the structure of an Sm3Ga5 − xSnx compound that crystallizes with the Pu3Pd5 structure within a wide compositional range. The considerable difference between the atomic scattering factors for Ga and Sn enables an accurate refinement of Ga/Sn distribution over three main-group atom positions.
In a single-crystal, extracted from an alloy of composition close to Sm3Ga2Sn3, the 8 g position (labelled Sn1 in Fig. 1) was found to be mostly occupied by Sn atoms (93% Sn and 7% Ga), while the 4c and 8f positions (Ga3/Sn3 and Ga2/Sn2, respectively) are occupied by a Ga/Sn statistical mixture, with a strong preference of Ga atoms for the 8f position (Table 1).
A powder diffraction study of ten Sm3Ga5 − xSnx samples has shown that the structure is preserved within 10 to 31 at.% of Ga. Cell parameters and nominal compositions for the eight single-phase samples are listed in Table 2. For all eight samples, the atomic positional and occupancy parameters were refined by the Rietveld method, in order to clarify the evolution of Ga/Sn site occupancies as a function of Ga content. As can be seen from the Fig. 2, within the limits of three standard uncertainties, the 8 g position remains exclusively occupied by Sn atoms over the whole concentration range. In contrast, Sn atoms in the 4c and 8f positions are gradually substituted by Ga, as the nominal Ga content increases.
The structure of the title compound can be described by a stacking along the c axis of two different layers (Fig. 1a). Layer A (z = 0 and z = 1/2, mapped by a mirror plane) is built of Sm1 and Ga2/Sn2 atoms in a distorted NaCl manner (Fig. 1 b). Layer B (z = 1/4 and z = 3/4, mapped by a 21 screw axis) is an ordered substitutional derivative of layer A (Fig. 1c): while the Ga/Sn position becomes fully occupied by Sn1 atoms, half of the Sm atoms are replaced with a Ga3/Sn3 statistical mixture. Thus, layer B corresponds to a distorted layer of the tetragonal InLiO2 structure type (Hoppe & Schepers, 1958), an ordered derivative of the NaCl structure type.
The shortest distances between the Sm and main-group element atoms correlate with the corresponding Ga/Sn occupancies. For the ordered atom Sn1, the distance is 3.1718 (7) Å, for Ga3/Sn3, nearly equally occupied by Ga and Sn atoms, it is 3.0775 (14) Å, and for the Ga-rich Ga2/Sn2 position, the shortest distance to an Sm atom is 3.0003 (10) Å (Table 3).
Table 1. Fractional atomic coordinates, occupancies and Wyckoff symbols for Sm3Ga1.89 (4)Sn3.11 (4).
Table 2. Cell parameters for the eight Sm3Ga0.80–2.48Sn4.20–2.52 (Sm37.5Ga10–31Sn52.5–31.5) single-phase samples.
Table 3. Selected interatomic distances (Å) in Sm3Ga1.89 (4)Sn3.11 (4).