Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270102005085/br1351sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270102005085/br1351Isup2.hkl |
The sample was weighed from pure thallium (Fluka, 4 N, mass?) and pure tellurium (Fluka, 5 N, mass?). Non-soluble impurities were removed from the tellurium by filtration under purified argon on silica wool. The thin oxide layer on the surface of the pure thallium pellets was removed using sulfuric acid baths (0.1 N) followed by rinsing in acetone. The alloy was then formed by direct fusion of the pure elements in a silica tube sealed under vacuum (10 -1 Pa). The composition of the alloy (xTe = 0.325) was chosen to ensure that the Tl2Te phase (xTe = 1/3) was obtained even in the event of evaporation or oxidation of thallium. Subsequent annealing was performed for 160 h at 553 K. For X-ray data collection, the crystal was covered by a protective layer of perfluoropolyalkylether (ABCR GmbH & Co.) to prevent its oxidation and decomposition.
Two non-coherent domains were identified in the crystal. The first domain had the Tl2Te structure and the second had a cubic face-centred lattice. The reflections of both domains were separated in the process of integrating the images. From 15502 measured reflections of the first domain, 2880 reflections were rejected because of the overlap with reflections of the second domain. The mean F2/σ(F2) = 4.6. In the second domain, 7317 reflections were measured and the mean F2/σ(F2) = 1.9. The R-factors show no systematic deviation of different reflection groups from the mean, whether in dependence on hkl or on Fobs or on sin(θ)/λ. No warnings of twinning were observed. Rint and the difference Fourier maps were calculated using 1989 observed reflections. The highest peaks in the difference Fourier map are closer than 1 Å to the atom sites.
Data collection: EXPOSE in IPDS Software (Stoe & Cie, 1999); cell refinement: CELL in IPDS Software; data reduction: ADDREF and SORTRF in Xtal (Hall et al., 2000), and TWIN in IPDS Software; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: LSLS in Xtal; molecular graphics: ATOMS (Dowty, 1993); software used to prepare material for publication: BONDLA and CIFIO in Xtal.
Tl2Te | F(000) = 9416 |
Mr = 536.37 | Dx = 9.084 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: -c 2yc | Cell parameters from 2000 reflections |
a = 15.6621 (9) Å | θ = 3–25° |
b = 8.9873 (4) Å | µ = 89.10 mm−1 |
c = 31.196 (2) Å | T = 293 K |
β = 100.761 (7)° | Parallelepiped, metallic dark grey |
V = 4313.9 (4) Å3 | 0.15 × 0.03 × 0.03 mm |
Z = 44 |
Stoe IPDS diffractometer | 1989 reflections with F2 > 2σ(F2) |
ϕ oscillation scans | Rint = 0.153 |
Absorption correction: analytical (X-RED; Stoe & Cie, 1999) | θmax = 25.9°, θmin = 2.6° |
Tmin = 0.019, Tmax = 0.127 | h = −19→19 |
12622 measured reflections | k = −11→10 |
3865 independent reflections | l = −38→38 |
Refinement on F2 | 0 constraints |
Least-squares matrix: full matrix | Weighting scheme based on measured s.u.'s |
R[F2 > 2σ(F2)] = 0.107 | (Δ/σ)max = 0.001 |
wR(F2) = 0.188 | Δρmax = 8.97 e Å−3 |
S = 2.37 | Δρmin = −8.32 e Å−3 |
1982 reflections | Extinction correction: B-C type 1 Gaussian isotropic |
150 parameters | Extinction coefficient: 0.005 |
0 restraints |
Tl2Te | V = 4313.9 (4) Å3 |
Mr = 536.37 | Z = 44 |
Monoclinic, C2/c | Mo Kα radiation |
a = 15.6621 (9) Å | µ = 89.10 mm−1 |
b = 8.9873 (4) Å | T = 293 K |
c = 31.196 (2) Å | 0.15 × 0.03 × 0.03 mm |
β = 100.761 (7)° |
Stoe IPDS diffractometer | 3865 independent reflections |
Absorption correction: analytical (X-RED; Stoe & Cie, 1999) | 1989 reflections with F2 > 2σ(F2) |
Tmin = 0.019, Tmax = 0.127 | Rint = 0.153 |
12622 measured reflections |
R[F2 > 2σ(F2)] = 0.107 | 150 parameters |
wR(F2) = 0.188 | 0 restraints |
S = 2.37 | Δρmax = 8.97 e Å−3 |
1982 reflections | Δρmin = −8.32 e Å−3 |
x | y | z | Uiso*/Ueq | ||
Tl1 | 0.46047 (12) | 0.7406 (3) | 0.69222 (5) | 0.038 (3) | |
Tl2 | 0.22052 (12) | 0.7372 (2) | 0.62040 (5) | 0.036 (3) | |
Tl3 | 0.30498 (12) | 0.0964 (2) | 0.68758 (5) | 0.031 (2) | |
Tl4 | 0.41703 (12) | 0.4103 (3) | 0.07023 (5) | 0.035 (3) | |
Tl5 | 0.00857 (12) | 0.7388 (2) | 0.64247 (6) | 0.040 (3) | |
Tl6 | 0.10549 (13) | 0.9425 (2) | 0.73832 (6) | 0.035 (3) | |
Tl7 | 0.14865 (12) | 0.4548 (2) | 0.69500 (5) | 0.050 (3) | |
Tl8 | 0.28563 (13) | 0.2439 (2) | 0.56210 (6) | 0.039 (3) | |
Tl9 | 0.36524 (13) | 0.5251 (2) | 0.46395 (6) | 0.045 (3) | |
Tl10 | 0.35436 (14) | 0.9243 (3) | 0.49974 (6) | 0.060 (4) | |
Tl11 | 0.41698 (14) | 0.0902 (3) | 0.41512 (6) | 0.040 (3) | |
Te1 | 0.3416 (2) | 0.4340 (4) | 0.64888 (8) | 0.055 (4) | |
Te2 | 0.6048 (2) | 0.5900 (3) | 0.62835 (8) | 0.053 (3) | |
Te3 | 0.3869 (2) | 0.9366 (3) | 0.60499 (8) | 0.049 (3) | |
Te4 | 0.26927 (19) | 0.7502 (4) | 0.72596 (7) | 0.055 (4) | |
Te5 | 0.53175 (19) | 0.7563 (4) | 0.48253 (8) | 0.055 (4) | |
Te6 | 0.50000 | 0.0988 (5) | 0.75000 | 0.030 (6) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Tl1 | 0.0342 (9) | 0.0417 (13) | 0.0415 (8) | 0.0014 (9) | 0.0003 (7) | 0.0114 (9) |
Tl2 | 0.0393 (10) | 0.0372 (12) | 0.0457 (8) | −0.0031 (9) | −0.0001 (7) | 0.0004 (10) |
Tl3 | 0.0384 (9) | 0.0349 (10) | 0.0284 (7) | −0.0005 (9) | 0.0005 (7) | 0.0042 (7) |
Tl4 | 0.0468 (12) | 0.0424 (13) | 0.0310 (8) | −0.0025 (10) | −0.0041 (8) | 0.0044 (8) |
Tl5 | 0.0298 (9) | 0.0339 (12) | 0.0795 (12) | 0.0037 (9) | −0.0011 (9) | −0.0076 (12) |
Tl6 | 0.0376 (10) | 0.0438 (14) | 0.0434 (9) | 0.0064 (9) | 0.0026 (8) | −0.0053 (9) |
Tl7 | 0.0474 (12) | 0.0440 (14) | 0.0325 (8) | −0.0085 (9) | −0.0078 (8) | 0.0063 (8) |
Tl8 | 0.0424 (10) | 0.0346 (13) | 0.0574 (9) | −0.0002 (9) | −0.0085 (8) | −0.0113 (10) |
Tl9 | 0.0433 (11) | 0.0452 (13) | 0.0379 (8) | −0.0013 (10) | 0.0014 (8) | −0.0008 (9) |
Tl10 | 0.0481 (12) | 0.0658 (16) | 0.0340 (8) | 0.0046 (11) | 0.0044 (8) | −0.0045 (9) |
Tl11 | 0.0574 (13) | 0.0593 (16) | 0.0411 (9) | −0.0082 (12) | 0.0139 (9) | −0.0088 (10) |
Te1 | 0.0420 (18) | 0.0305 (18) | 0.0290 (13) | 0.0035 (15) | 0.0052 (12) | −0.0010 (12) |
Te2 | 0.0343 (15) | 0.0251 (17) | 0.0333 (13) | 0.0063 (14) | −0.0010 (11) | −0.0040 (12) |
Te3 | 0.0474 (18) | 0.0237 (17) | 0.0252 (12) | 0.0056 (14) | 0.0089 (12) | 0.0059 (12) |
Te4 | 0.0325 (14) | 0.0247 (18) | 0.0328 (12) | 0.0006 (14) | 0.0077 (10) | −0.0029 (15) |
Te5 | 0.0334 (14) | 0.0233 (18) | 0.0405 (13) | −0.0034 (13) | 0.0046 (11) | 0.0030 (14) |
Te6 | 0.0162 (18) | 0.034 (3) | 0.0320 (17) | 0.00000 | −0.0008 (15) | 0.00000 |
Tl1—Te3 | 3.266 (3) | Tl4—Tl9 | 3.897 (3) |
Tl1—Te4 | 3.356 (4) | Tl4—Tl5 | 3.984 (3) |
Tl1—Te1 | 3.457 (4) | Tl5—Te1 | 3.186 (4) |
Tl1—Tl7i | 3.508 (3) | Tl5—Te3 | 3.397 (4) |
Tl1—Te2 | 3.550 (4) | Tl5—Tl7 | 3.560 (3) |
Tl1—Tl1 | 3.586 (2) | Tl5—Te2 | 3.560 (4) |
Tl1—Tl6 | 3.631 (3) | Tl5—Tl6 | 3.592 (3) |
Tl1—Te6 | 3.685 (4) | Tl5—Te6 | 3.609 (3) |
Tl1—Tl6 | 3.712 (3) | Tl5—Tl11 | 3.757 (3) |
Tl1—Tl4 | 3.977 (2) | Tl5—Tl8 | 3.900 (3) |
Tl1—Tl2 | 4.000 (2) | Tl6—Te4 | 3.175 (4) |
Tl1—Tl3 | 4.005 (3) | Tl6—Te4 | 3.453 (4) |
Tl2—Te4 | 3.241 (3) | Tl6—Te1 | 3.462 (3) |
Tl2—Te3 | 3.272 (4) | Tl6—Tl6 | 3.514 (3) |
Tl2—Te1 | 3.344 (4) | Tl6—Te6 | 3.554 (4) |
Tl2—Tl9 | 3.460 (3) | Tl6—Te2 | 3.676 (3) |
Tl2—Tl5 | 3.514 (3) | Tl6—Tl7 | 4.022 (3) |
Tl2—Te2 | 3.683 (4) | Tl7—Te4 | 3.151 (3) |
Tl2—Tl11 | 3.692 (3) | Tl7—Te4 | 3.297 (4) |
Tl2—Tl7 | 3.756 (3) | Tl7—Te6 | 3.396 (3) |
Tl2—Tl4 | 3.934 (3) | Tl7—Tl11 | 3.421 (2) |
Tl2—Tl3 | 3.940 (3) | Tl7—Te1 | 3.586 (4) |
Tl2—Tl10 | 3.986 (2) | Tl8—Te1 | 3.182 (3) |
Tl3—Te6 | 3.3016 (17) | Tl8—Te3 | 3.338 (4) |
Tl3—Te2 | 3.329 (3) | Tl8—Tl9 | 3.372 (3) |
Tl3—Te1 | 3.354 (4) | Tl8—Te5 | 3.407 (4) |
Tl3—Te3 | 3.403 (3) | Tl8—Tl11 | 3.693 (3) |
Tl3—Te4 | 3.417 (4) | Tl8—Tl10 | 3.739 (3) |
Tl3—Te4 | 3.422 (3) | Tl8—Tl8 | 3.828 (2) |
Tl3—Tl7 | 3.817 (2) | Tl8—Tl10 | 3.980 (3) |
Tl3—Tl5 | 3.932 (3) | Tl9—Te2 | 3.175 (3) |
Tl3—Tl6 | 3.972 (3) | Tl9—Te5 | 3.283 (4) |
Tl3—Tl6 | 4.003 (3) | Tl9—Te5 | 3.300 (4) |
Tl3—Tl7 | 4.079 (3) | Tl9—Tl10 | 3.770 (3) |
Tl3—Tl8 | 4.090 (2) | Tl9—Tl10 | 3.844 (3) |
Tl4—Te2 | 3.154 (3) | Tl10—Te3 | 3.229 (3) |
Tl4—Te1 | 3.234 (4) | Tl10—Te5 | 3.293 (4) |
Tl4—Tl9 | 3.314 (2) | Tl10—Tl11 | 3.335 (3) |
Tl4—Te3 | 3.363 (4) | Tl10—Te5 | 3.371 (4) |
Tl4—Te5 | 3.676 (4) | Tl10—Tl11 | 4.043 (3) |
Tl4—Tl8 | 3.710 (3) | Tl11—Te2 | 3.170 (4) |
Tl4—Tl10 | 3.746 (3) | Tl11—Te3 | 3.256 (4) |
Tl4—Te5 | 3.846 (4) | Tl11—Te5 | 3.433 (3) |
Tl4—Tl11 | 3.847 (3) |
Symmetry code: (i) x+1/2, y+1/2, z. |
Experimental details
Crystal data | |
Chemical formula | Tl2Te |
Mr | 536.37 |
Crystal system, space group | Monoclinic, C2/c |
Temperature (K) | 293 |
a, b, c (Å) | 15.6621 (9), 8.9873 (4), 31.196 (2) |
β (°) | 100.761 (7) |
V (Å3) | 4313.9 (4) |
Z | 44 |
Radiation type | Mo Kα |
µ (mm−1) | 89.10 |
Crystal size (mm) | 0.15 × 0.03 × 0.03 |
Data collection | |
Diffractometer | Stoe IPDS diffractometer |
Absorption correction | Analytical (X-RED; Stoe & Cie, 1999) |
Tmin, Tmax | 0.019, 0.127 |
No. of measured, independent and observed [F2 > 2σ(F2)] reflections | 12622, 3865, 1989 |
Rint | 0.153 |
(sin θ/λ)max (Å−1) | 0.615 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.107, 0.188, 2.37 |
No. of reflections | 1982 |
No. of parameters | 150 |
Δρmax, Δρmin (e Å−3) | 8.97, −8.32 |
Computer programs: EXPOSE in IPDS Software (Stoe & Cie, 1999), CELL in IPDS Software, ADDREF and SORTRF in Xtal (Hall et al., 2000), and TWIN in IPDS Software, SHELXS97 (Sheldrick, 1997), LSLS in Xtal, ATOMS (Dowty, 1993), BONDLA and CIFIO in Xtal.
Tl1—Te3 | 3.266 (3) | Tl5—Te2 | 3.560 (4) |
Tl1—Te4 | 3.356 (4) | Tl5—Tl6 | 3.592 (3) |
Tl1—Te1 | 3.457 (4) | Tl6—Te4 | 3.175 (4) |
Tl1—Tl7i | 3.508 (3) | Tl6—Te4 | 3.453 (4) |
Tl1—Tl1 | 3.586 (2) | Tl6—Te1 | 3.462 (3) |
Tl1—Tl6 | 3.631 (3) | Tl6—Tl6 | 3.514 (3) |
Tl2—Te4 | 3.241 (3) | Tl7—Te4 | 3.151 (3) |
Tl2—Te3 | 3.272 (4) | Tl7—Te4 | 3.297 (4) |
Tl2—Te1 | 3.344 (4) | Tl7—Te6 | 3.396 (3) |
Tl2—Tl9 | 3.460 (3) | Tl7—Tl11 | 3.421 (2) |
Tl2—Tl5 | 3.514 (3) | Tl8—Te1 | 3.182 (3) |
Tl2—Tl11 | 3.692 (3) | Tl8—Te3 | 3.338 (4) |
Tl3—Te6 | 3.3016 (17) | Tl8—Tl9 | 3.372 (3) |
Tl3—Te2 | 3.329 (3) | Tl8—Te5 | 3.407 (4) |
Tl3—Te1 | 3.354 (4) | Tl8—Tl11 | 3.693 (3) |
Tl3—Te3 | 3.403 (3) | Tl8—Tl10 | 3.739 (3) |
Tl3—Te4 | 3.417 (4) | Tl9—Te2 | 3.175 (3) |
Tl3—Te4 | 3.422 (3) | Tl9—Te5 | 3.283 (4) |
Tl4—Te2 | 3.154 (3) | Tl9—Te5 | 3.300 (4) |
Tl4—Te1 | 3.234 (4) | Tl10—Te3 | 3.229 (3) |
Tl4—Tl9 | 3.314 (2) | Tl10—Te5 | 3.293 (4) |
Tl4—Te3 | 3.363 (4) | Tl10—Tl11 | 3.335 (3) |
Tl4—Te5 | 3.676 (4) | Tl10—Te5 | 3.371 (4) |
Tl4—Te5 | 3.846 (4) | Tl11—Te2 | 3.170 (4) |
Tl5—Te1 | 3.186 (4) | Tl11—Te3 | 3.256 (4) |
Tl5—Te3 | 3.397 (4) | Tl11—Te5 | 3.433 (3) |
Tl5—Tl7 | 3.560 (3) |
Symmetry code: (i) x+1/2, y+1/2, z. |
Although the existence of Tl2Te has been reported by many authors (Hahn & Klinger 1949; Rabenau et al., 1960; Vasilev et al., 1968; Asadov et al., 1977; Chami et al., 1983), its crystal structure has remained undetermined, and its existence has even been questioned (Chikashige, 1912; Klemm & Vogel, 1934; Oh & Lee, 1993). Using differential scanning calorimetry and powder X-ray diffraction, a study of the Tl—Te phase diagram was undertaken by Record et al. (1997), in which the existence of this phase was unambiguously confirmed. We report here on the crystal structure of Tl2Te and its relation to Tl5Te3.
The crystal structure of Tl2Te can be described as two alternating types of (h0h) layers, similar to those found in the structure of Tl5Te3 [Fig. 1. in Schewe et al. (1989)]. Layer type A is a quasi-planar layer at x + z = 0, 1/2, 1 and 3/2. Layer type B is a puckered layer (thickness 2.5 Å) at x + z = 1/4, 3/4, 5/4 and 7/4. Layer A (Fig. 1) corresponds to the layer found at z = 0 and 1/2 in Tl5Te3, while layer B (Fig. 1) corresponds to the layer found at z = 1/4 and 3/4 in Tl5Te3.
Layer A is described in Tl5Te3 as being formed from a 32434 net of Te atoms centred by a 44 net of Tl atoms. Bands of width ~18.3 Å containing basic motifs of this net are formed from atoms Tl3, Tl4, Te1, Te3, Te4 and Te5 in the structure of Tl2Te. These bands are oriented along the b axis and are repeated twice in the [101] direction of the cell of Tl2Te. Neighbouring bands are mutually shifted from the ideal infinite nets found in Tl5Te3 by a vector lying in the (h0h) plane having a length of ~4.85 Å (Fig. 1). The composition of layer A is identical in Tl2Te (Tl8Te16) and in Tl5Te3 (Tl4Te8).
Layer B is described in Tl5Te3 as being formed from a 482 net of Tl atoms centred by a 44 net of Te atoms. Bands of width ~14.7 Å containing basic motifs of this net are formed from atoms Tl1, Tl2, Tl5, Tl6, Tl7, Tl8, Tl9, Tl10, Tl11, Te2 and Te6 in the structure of Tl2Te. The bands are also oriented along the b axis and are repeated twice in the [101] direction of the cell of Tl2Te. Neighbouring bands are again mutually shifted by the same vector as in layer A, and are separated by atomic chains containing only Tl atoms. The composition of layer B in Tl2Te is Tl36Te6, compared with Tl16Te4 in Tl5Te3. The overall composition changes from Tl5Te3 to Tl2Te.
The shears in layers A and B occur so that they form (002) shear planes. The stacking of layers A and B in the structure of Tl2Te, and the relation between the elementary cells of Tl2Te and Tl5Te3, are given in Fig. 2.
The structure of Tl5Te3 has also been described as containing infinite straight Te—Tl—Te chains, with Tl—Te distances of 3.15 Å, and quasimolecular Tl2Te groups, with Tl—Te distances of 3.16 Å. These chains propagate along the direction perpendicular to layers A and B. They can also be identified in the structure of Tl2Te. However, they are finite (Tl4—Te2—Tl3—Te6—Tl3—Te2—Tl4), because of the shears in the A and B layers, and distorted (Tl—Te distances between 3.14 and 3.34 Å). The Tl2Te groups can also be found in the structure of Tl2Te. However, the Tl—Te distance in the group varies between 3.15 and 3.30 Å.
The coordination of Tl and Te atoms in the structure of Tl2Te is derived from that in the structure of Tl5Te3. The Tl atoms lying in the A layer of the Tl5Te3 structure are coordinated by a Te4 + 2 octahedron in the first sphere and by a Tl8 cube in the second sphere. This coordination is nearly preserved in the Tl2Te structure for atom Tl3, with slightly longer Tl—Te distances (3.30–3.42 Å) in the Te6 octahedron and in the deformed Tl8 cube (Tl—Tl distances of 3.82–4.09 Å). For atom Tl4, lying on the shear plane, the coordination is Te5 (Tl—Te distances of 3.15–3.85 Å), and Tl8 (Tl—Tl distances of 3.32–3.99 Å).
The Tl atoms in the B layer of the Tl2Te structure are coordinated in the first sphere in a way similar to the Tl atoms in the B layer of the Tl5Te3 structure (distorted trigonal prism, Te3Tl3), with Tl—Te distances 3.15–3.54 Å and Tl—Tl distances 3.35–3.73 Å. The Tl9—Tl4 (3.32 Å), Tl9—Tl8 (3.37 Å) and Tl10—Tl11 (3.35 Å) distances, found near the shear plane, correspond well with the distance in metallic Tl (3.35 Å).
The Te atoms in the A layer of the Tl2Te structure lying outside the shear plane (atoms Te1, Te3 and Te4) are coordinated in a similar way to the Te atoms in the A layer of the Tl5Te3 structure (distorted bicapped trigonal prism, Tl8), with Te—Tl distances of 3.15–3.58 Å. Atom Te5 lying on the shear plane is coordinated by a distorted trigonal prism, Tl6, with Te—Tl distances of 3.30–3.43 Å. Atom Te6 lying in the B layer outside the shear plane is coordinated as in the Tl5Te3 structure, by a compressed bicapped tetragonal antiprism, with Te—Tl distances of 3.31–3.69 Å. Atom Te2 lying in the B layer close to the shear plane is coordinated by a distorted tetragonal antiprism, with Te—Tl distances of 3.14–3.68 Å.
The crystal structure of Tl2Te can be rationalized as being composed from regions with the structure of Tl5Te3 and regions which contain only Tl atoms, some of them showing Tl—Tl distances corresponding to metallic Tl. This description is further supported by the decomposition of Tl2Te into Tl5Te3 and Tl upon heating (Rabenau et al., 1960; Vasilev et al., 1968; Schewe et al., 1989). We have observed such phase transformation on a bulk sample of Tl2Te, by powder diffraction and Rietveld refinement. After several days of the sample being exposed to air, it had nearly completely transformed to the Tl5Te3 phase and thallium oxides. According to the analysis of the Tl5Te3 structure in Schewe et al. (1989), the bond analysis of the Tl—Te system in Bhan & Schubert (1970), the chemical composition and the absence of Te—Te bonds in the structure of Tl2Te, we expect that Tl has the oxidation state Tl1+ in Tl2Te, and the compound is metallic.
The structures of Tl5Te3 and Tl2Te are closely related, and indeed the crystal studied here was intergrown from two domains, one with the Tl2Te structure and the other having a cubic face-centred lattice, with ac = 12.70 Å. The diffraction pattern of the Tl5Te3 structure shows a strong face-centred cubic pseudosymmetry, with ac = 12.60 Å, following the relation at = 1/2(-ac + cc) = 8.98 Å, bt = 1/2(ac + cc) = 8.98 Å and ct = bc = 12.60 Å. Some authors have even reported a diffraction pattern corresponding to a cubic lattice, with the lattice parameter \sim 12.60 Å (Man et al., 1971; Anseau, 1973).
The Tl5Te3 phase shows a small range of homogeneity of several at.% Tl. Whether, within this homogeneity range, the structure can change from pseudocubic to true cubic, and whether our second domain corresponds to that cubic structure or to the tetragonal Tl5Te3 structure, cannot be answered here, because of the small size of the second domain. The monoclinic cell of the Tl2Te structure can also be related to the cubic cell with ac = 12.70 Å. However, the deviation from the cubic lattice is much bigger than in the case of the tetragonal Tl5Te3 cell. We have observed the following relation between the lattices of the first domain (monoclinic) and the second domain (cubic) with ac = 12.70 Å: am ~1/2(-ac + 2bc - cc) = 15.55 Å, bm = 1/2(-ac + cc) = 8.98 Å and cm ~2ac + bc + 2cc = 28.40 Å.