Tl2Te and its relationship with Tl5Te3

Article abstract of DOI:10.1107/S0108270102005085

The crystal structure of dithallium telluride was determined using the single crystal X ray diffraction. The structural relationship of dithallium telluride with the related Tl₅Te₃ phase was discussed. The crystal structure of dithal

Full text of DOI:10.1107/S0108270102005085

inorganic compounds
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
Acta Crystallographica Section C
Crystal Structure
Ê
Communications
ꢀ14.7 A containing basic motifs of this net are formed from
ISSN 0108-2701
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.
Tl2Te and its relationship with Tl5Te3
a
b
a
Ï
Â
Radovan Cerny, * Jean-Marc Joubert, Yaroslav Filinchuk
and Yves Feutelaisc
a
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.
Â
Á
Laboratoire de Cristallographie, Universite de Geneve, 24 quai Ernest-Ansermet,
b
Á
Â
CH-1211 Geneve 4, Switzerland, Laboratoire de Chimie Metallurgique des Terres
Rares, CNRS, 2-8 rue Henri Dunant, 94320 Thiais, France, and cLaboratoire de
Â
Â
Chimie Physique, Minerale et Bioinorganique, EA 401, Faculte de Pharmacie, 5 rue
Â
Ã
J.-B. Clement, 92296 Chatenay-Malabry, France
The structure of Tl5Te3 has also been described as
containing in®nite straight TeÐTlÐTe chains, with TlÐTe
Correspondence e-mail: radovan.cerny@cryst.unige.ch
Ê
distances of 3.15 A, and quasi-molecular Tl2Te groups, with
Ê
TlÐTe distances of 3.16 A. These chains propagate along the
direction perpendicular to layers A and B. They can also be
identi®ed in the structure of Tl2Te. However, they are ®nite
(Tl4ÐTe2ÐTl3ÐTe6ÐTl3ÐTe2ÐTl4), because of the shears
in the A and B layers, and distorted (TlÐTe distances between
Received 26 October 2001
Accepted 19 March 2002
Online 19 April 2002
The crystal structure of Tl2Te, dithallium telluride, has been
determined by single-crystal X-ray diffraction. The analysis of
the structure shows that this compound is the ®rst known
representative of a new crystal structure type. The structural
relationship with the related Tl5Te3 phase is discussed.
Ê
3.14 and 3.34 A). The Tl2Te groups can also be found in the
structure of Tl2Te. However, the TlÐTe distance in the group
Ê
varies between 3.15 and 3.30 A.
Comment
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
existenceofthisphasewasunambiguouslycon®rmed.Wereport
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, 12, 1 and 23. Layer type B is
1
3
5
7
Ê
a puckered layer (thickness 2.5 A) at x + z = 4, 4, 4 and 4. Layer
1
A (Fig. 1) corresponds to the layer found at z = 0 and in
Tl5Te3, while layer B (Fig. 1) corresponds to the layer found at
2
1
z = and 3 in Tl5Te3.
4
4
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
Ê
ꢀ18.3 A 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 in®nite nets found in
Tl5Te3 by a vector lying in the (h0h) plane having a length of
Figure 1
The structure of Tl2Te viewed in the direction ꢀ[301]. Two basic units, the
planar layer A and the puckered layer B, are shown. Open circles indicate
Tl atoms and ®lled circles indicate Te atoms. Only the Te net in layer A
and the Tl net in layer B are shown. The position of the shear plane is
marked by a dashed line in each unit. The shear vector between two
Tl5Te3-like regions is also shown.
Ê
ꢀ4.85 A (Fig. 1). The composition of layer A is identical in
Tl2Te (Tl8Te16) and in Tl5Te3 (Tl4Te8).
Acta Cryst. (2002). C58, i63±i65
DOI: 10.1107/S0108270102005085
# 2002 International Union of Crystallography i63

inorganic compounds
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 coordi-
nated by a Te4+2 octahedron in the ®rst sphere and by a Tl8
cube in the second sphere. This coordination is nearly
preserved in the Tl2Te structure for atom Tl3, with slightly
Rietveld re®nement. 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 by Schewe et al. (1989), the bond analysis
of the TlÐTe system by Bhan & Schubert (1970), the chemical
composition and the absence of TeÐTe bonds in the structure
of Tl2Te, we expect that Tl has the oxidation state Tl1+ in
Tl2Te, and that the compound is metallic.
Ê
longer TlÐTe distances (3.30±3.42 A) in the Te6 octahedron
and in the deformed Tl8 cube (TlÐTl distances of 3.82±
Ê
4.09 A). For atom Tl4, lying on the shear plane, the coordi-
Ê
nation is Te5 (TlÐTe distances of 3.15±3.85 A) and Tl8 (TlÐTl
Ê
distances of 3.32±3.99 A).
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
Ê
The Tl atoms in the B layer of the Tl2Te structure are
coordinated in the ®rst sphere in a way similar to the Tl atoms
in the B layer of the Tl5Te3 structure (distorted trigonal prism,
cubic face-centred lattice, with ac = 12.70 A. The diffraction
pattern of the Tl5Te3 structure shows a strong face-centred
Ê
cubic pseudosymmetry, with ac = 12.60 A, following the rela-
Ê
tionship at = 2( ac + cc) = 8.98 A, bt = 2(ac + cc) = 8.98 A and
1
1
Ê
Ê
Te3Tl3), with TlÐTe distances 3.15±3.54 A and TlÐTl
Ê
distances of 3.35±3.73 A. The Tl9ÐTl4 (3.32 A), Tl9ÐTl8
Ê
Ê
ct = bc = 12.60 A. Some authors have even reported a
diffraction pattern corresponding to a cubic lattice, with a
Ê
(3.37 A) and Tl10ÐTl11 (3.35 A) distances, found near the
Ê
Ê
lattice parameter of approximately 12.60 A (Man et al., 1971;
Anseau, 1973).
shear plane, correspond well with the distance in metallic Tl
Ê
(3.35 A).
The Te atoms in the A layer of the Tl2Te structure lying
outside the shear plane (atoms Te1, Te3 and Te4) are coor-
dinated in a similar way to the Te atoms in the A layer of the
Tl5Te3 structure (distorted bicapped trigonal prism, Tl8), with
The Tl5Te3 phase shows a small range of homogeneity of
several atomic% Tl. Whether, within this homogeneity range,
the structure can change from pseudocubic to true cubic, and
whether our second domain corresponds to that cubic struc-
ture 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
Ê
TeÐTl distances of 3.15±3.58 A. Atom Te5, lying on the shear
plane, is coordinated by a distorted trigonal prism, Tl6, with
Ê
TeÐTl distances of 3.30±3.43 A. Atom Te6, lying in the B
Ê
layer outside the shear plane, is coordinated as in the Tl5Te3
structure, by a compressed bicapped tetragonal antiprism,
Ê
with TeÐTl distances of 3.31±3.69 A. Atom Te2, lying in the B
layer close to the shear plane, is coordinated by a distorted
cubic cell with ac = 12.70 A. However, the deviation from the
cubic lattice is much greater than in the case of the tetragonal
Tl5Te3 cell. We have observed the following relationship
between the lattices of the ®rst domain (monoclinic) and the
1
2
Ê
tetragonal antiprism, with TeÐTl distances of 3.14±3.68 A.
Ê
second domain (cubic) with ac = 12.70 A: am ꢀ ( ac + 2bc
1
2
Ê
Ê
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
TlÐTl distances corresponding to metallic Tl. This description
is further supported by the decomposition of Tl2Te into Tl5Te3
and Tl on heating (Rabenau et al., 1960; Vasilev et al., 1968;
Schewe et al., 1989). We have observed such phase transfor-
mation on a bulk sample of Tl2Te, by powder diffraction and
cc) = 15.55 A, bm = ( ac + cc) = 8.98 A and cm ꢀ 2ac + bc
Ê
+ 2cc = 28.40 A.
Experimental
The analytical sample was composed of weighed samples of pure
thallium (Fluka, 4 N, 0.995 g) and pure tellurium (Fluka, 5 N,
0.299 g). Non-soluble impurities were removed from the tellurium by
®ltration under puri®ed 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 = 0.333) was obtained
even in the event of evaporation or oxidation of the thallium.
Subsequent annealing was performed for 160 h at 553 K. For X-ray
data collection, the crystal was covered with a protective layer of
per¯uoropolyalkyl ether (ABCR GmbH & Co.) to prevent its
oxidation and decomposition.
Crystal data
3
Tl2Te
Mr = 536.37
Monoclinic, C2=c
Dx = 9.084 Mg m
Mo Kꢁ radiation
Cell parameters from 2000
re¯ections
Ê
a = 15.6621 (9) A
b = 8.9873 (4) A
ꢂ = 3±25ꢂ
ꢃ = 89.10 mm
T = 293 K
Figure 2
Ê
1
Ê
The stacking of layers A and B in the structure of Tl2Te viewed in the
[010] direction. The Tl2Te cell is shown by a solid line and the Tl5Te3 cell
by a dashed line. Open circles indicate Tl atoms and ®lled circles indicate
Te atoms. The position of the shear plane is marked by a dashed line.
c = 31.196 (2) A
ꢀ = 100.761 (7)ꢂ
Ê
V = 4313.9 (4) A
Z = 44
3
Parallelepiped, metallic dark grey
0.15 Â 0.03 Â 0.03 mm
Ï
ꢁ
Â
i64 Radovan Cerny et al.
Tl2Te
Acta Cryst. (2002). C58, i63±i65

inorganic compounds
Table 1
Selected interatomic distances (A).
centred lattice. The re¯ections of both domains were separated in the
process of integrating the images. From 15 502 measured re¯ections
of the ®rst domain, 2880 re¯ections were rejected because of overlap
with re¯ections of the second domain and mean F2/ꢄ(F2) = 4.6. In the
second domain, 7317 re¯ections were measured and mean F2/ꢄ(F2) =
1.9. The R factors show no systematic deviation of different re¯ection
groups from the mean, whether in dependence on hkl, Fobs or sin(ꢂ)/
ꢆ. No warnings of twinning were observed. The value of Rint and the
difference Fourier maps were calculated using 1989 observed re¯ec-
Ê
Tl1ÐTe3
Tl1ÐTe4
Tl1ÐTe1
Tl1ÐTl7i
Tl1ÐTl1ii
Tl1ÐTl6iii
Tl2ÐTe4
Tl2ÐTe3
Tl2ÐTe1
Tl2ÐTl9iv
Tl2ÐTl5
3.266 (3)
3.356 (4)
3.457 (4)
3.508 (3)
3.586 (2)
3.631 (3)
3.241 (3)
3.272 (4)
3.344 (4)
3.460 (3)
3.514 (3)
3.692 (3)
3.3016 (17)
3.329 (3)
3.354 (4)
3.403 (3)
3.417 (4)
3.422 (3)
3.154 (3)
3.234 (4)
3.314 (2)
3.363 (4)
3.676 (4)
3.846 (4)
3.186 (4)
3.397 (4)
3.560 (3)
Tl5ÐTe2xi
Tl5ÐTl6
3.560 (4)
3.592 (3)
3.175 (4)
3.453 (4)
3.462 (3)
3.514 (3)
3.151 (3)
3.297 (4)
3.396 (3)
3.421 (2)
3.182 (3)
3.338 (4)
3.372 (3)
3.407 (4)
3.693 (3)
3.739 (3)
3.175 (3)
3.283 (4)
3.300 (4)
3.229 (3)
3.293 (4)
3.335 (3)
3.371 (4)
3.170 (4)
3.256 (4)
3.433 (3)
Tl6ÐTe4
Tl6ÐTe4xii
Tl6ÐTe1xii
Tl6ÐTl6xiii
Tl7ÐTe4viii
Tl7ÐTe4
Tl7ÐTe6xi
Tl7ÐTl11v
Tl8ÐTe1
Tl8ÐTe3vii
Tl8ÐTl9v
Ê
tions. The highest peaks in the difference Fourier map are within 1 A
of the atom sites.
Tl2ÐTl11v
Tl3ÐTe6
Tl3ÐTe2vi
Tl3ÐTe1
Tl3ÐTe3vii
Tl3ÐTe4vii
Tl3ÐTe4viii
Tl4ÐTe2ix
Tl4ÐTe1ix
Tl4ÐTl9ix
Tl4ÐTe3ix
Tl4ÐTe5x
Tl4ÐTe5ix
Tl5ÐTe1xi
Tl5ÐTe3vi
Tl5ÐTl7
Data collection: EXPOSE in IPDS Software (Stoe & Cie, 1999);
cell re®nement: CELL in IPDS Software; data reduction: ADDREF
and SORTRF in Xtal3.7 (Hall et al., 2000), and TWIN in IPDS
Software; program(s) used to solve structure: SHELXS97 (Sheldrick,
1997); program(s) used to re®ne structure: LSLS in Xtal3.7; mole-
cular graphics: ATOMS (Dowty, 1993); software used to prepare
material for publication: BONDLA and CIFIO in Xtal3.7.
Tl8ÐTe5xiv
Tl8ÐTl11v
Tl8ÐTl10vii
Tl9ÐTe2xiv
Tl9ÐTe5xiv
Tl9ÐTe5
Tl10ÐTe3
Tl10ÐTe5
Tl10ÐTl11xv
Tl10ÐTe5xvi
Tl11ÐTe2xiv
Tl11ÐTe3xiv
Tl11ÐTe5xiv
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: BR1351). Services for accessing these data are
described at the back of the journal.
1
1
2
Symmetry codes: (i) ‡ x; 12 ‡ y; z; (ii)
1
x; y; 32 z; (iii) ‡ x; y 12; z; (iv)
2
1
x; 32 y; 1 z; (v)
x; 12 y; 1 z; (vi)
x
12; y 12; z; (vii) x; y 1; z; (viii)
1
2
2
References
1
2
1
1
2
3
2
1
2
1 1
2 2
x; y
;
z; (ix) x; 1 y; z
x; 12 ‡ y; 32 z; (xiii) x; y; 32 z; (xiv)
;
(x)
1
1
x; y; 12 z; (xi)
x
;
‡ y; z; (xii)
x; 1 y; 1 z; (xv) x; 1 ‡ y; z; (xvi)
2
Anseau, M. R. (1973). J. Appl. Phys. 44, 3357±3359.
Asadov, M. M., Babanly, M. B. & Kuliev, A. A. (1977). Inorg. Mater. 13, 1137±
1140.
1
x; 2 y; 1 z.
Data collection
Becker, P. J. & Coppens, P. (1974). Acta Cryst. A30, 148±153.
Bhan, S. & Schubert, K. (1970). J. Less Common Met. 20, 229±235.
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Stoe IPDS diffractometer
' oscillation scans
Rint = 0.153
max = 25.9ꢂ
ꢂ
Absorption correction: analytical
(X-RED; Stoe & Cie, 1999)
Tmin = 0.019, Tmax = 0.127
12 622 measured re¯ections
3865 independent re¯ections
1989 re¯ections with F2 > 2ꢄ(F2)
h = 19 ! 19
k = 11 ! 10
l = 38 ! 38
200 standard re¯ections
frequency: 10 min
intensity decay: none
Re®nement
Re®nement on F2
R(F) = 0.107
(Á/ꢄ)max = 0.001
3
Ê
Áꢅmax = 8.97 e A
wR(F2) = 0.180
S = 2.37
Áꢅmin
=
3
Ê
8.32 e A
Extinction correction: B±C type 1
Gaussian isotropic (Becker &
Coppens, 1974)
1982 re¯ections
150 parameters
Weighting scheme based on
measured s.u.'s
Sheldrick, G. M. (1997). SHELXS97. University of GoÈttingen, Germany.
Stoe & Cie (1999). X-RED (Version 1.19) and IPDS Software (Version 2.92).
Stoe & Cie, Darmstadt, Germany.
Extinction coef®cient: 0.005
Two non-coherent domains were identi®ed in the crystal. The ®rst
domain had the Tl2Te structure and the second had a cubic face-
Vasilev, V. P., Nikolskaya, A. V., Gerasimov, Ya. I. & Kusnetzov, A. F. (1968).
Inorg. Mater. 4, 914±919.
Ï
ꢁ
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Acta Cryst. (2002). C58, i63±i65
Radovan Cerny et al. Tl2Te i65