TeO2-WO3 glasses: Infrared, XPS and XANES structural characterizations

Article abstract of DOI:10.1006/jssc.2002.9707

Transparent (1-x)TeO₂-xWO₃ glasses with 0≤x≤0.325 mol were synthesized by the fast quenching technique. Several complementary techniques as infrared, X-ray photoelectron and X-ray absorption spectroscopies were used to approach the s

Full text of DOI:10.1006/jssc.2002.9707

Journal of Solid State Chemistry 168, 175–183 (2002)
doi:10.1006/jssc.2002.9707
TeO ^WO Glasses: Infrared, XPS and XANES
2
3
Structural Characterizations
n
,1
n
P. Charton, L. Gengembre,w and P. Armand
n
LPMC, UMR CNRS 5617, UMII, c.c. 003, Place E. Bataillon, 34095 Montpellier Cedex 5, France; and wUniversit e! des Sciences et Technologies de Lille,
Laboratoire de Catalyse, CNRS-UPRESA 8010, B a# t. C3, 59655 Villeneuve d’Ascq Cedex, France
Received March 14, 2002; in revised form June 24, 2002; accepted July 16, 2002
(XPS) spectroscopies were undertaken, in our knowledge,
Transparent (1ꢀx)TeO –xWO glasses with 0rxr0.325 mol on these tungsten-oxide glasses.
2
3
were synthesizedby the fast quenching technique. Several
complementary techniques as infrared, X-ray photoelectron
andX-ray absorption spectroscopies were usedto approach
the structure of these tungsten oxide–tellurite glasses. Special
attention was paid to the oxidation state and the coordination
state of tungsten atoms. The structural results show that
Despite many characterizations, the structure of TeO2–
WO glasses is still subject to discussion. Indeed, some
3
authors agree with the evolution of the TeO4 trigonal
bipyramid polyhedra with the increase in WO content
3
(8, 10), while some authors have the opinion that WO does
3
not lead to a Te coordination change (7, 11). The same
discussion exists concerning the tungsten coordination
(
1ꢀx)TeO –xWO glasses present characteristic tellurium
2
3
environments which vary with their chemical composition while
tungsten ions always adopt an octahedral configuration. # 2002
Elsevier Science (USA)
sphere, i.e., existence of WO4 tetrahedra or/and WO6
octahedra (2, 7, 9).
The purpose of this paper was to approach the structure
Key Words: oxide glasses; tellurite; tungsten oxide; infrared;
X-ray photoelectron spectroscopy; X-ray absorption; XANES; of glasses obtained in the TeO –WO system by several
2
3
XPS; TeO2.
complementary techniques; infrared, X-ray photoelectron
and XANES. Special attention was paid to the oxidation
state and the coordination state of tungsten atoms.
2
. EXPERIMENTAL CONSIDERATIONS
1. INTRODUCTION
2
.1. Sample Preparation
The synthesis of glasses with high refractive index values
is of great importance in the glass science and the optical
industries. Tungsten oxide–tellurite glasses have been
obtained showing an extremely high refractive index with
low dispersion value, low crystallization ability and good
chemical resistance (1, 2). Also, they exhibit good light
transmission in the visible and near infrared regions up to
The glass samples were prepared by melting mixtures of
analytic grade reagents of a-TeO and g-WO in an electric
furnace heated up to 9001C. The platinum crucible
containing the melt was quickly quenched in an ice-cold
water bath to avoid crystallization. In order to extend the
glass-forming domain and to improve the samples quality
2
3
(homogeneity), some preparations were quenched in a
5
.5 mm (3). For these reasons, TeO –WO glasses have
2
3
freezing mixture (ꢀ101C) made of ethanol, ice and NaCl.
Indeed, it is the only way to prepare pure TeO glass (12)
(13). The amorphous state of each sample was checked by
become the subject of several investigations. The glass
formation domain has been determined and the thermal
parameters examined by several authors (1, 4, 5). Neutron
scattering experiments and vibrational spectroscopy stu-
dies, especially Raman analysis, were conducted to follow
the effect of WO on the structure of tellurite glasses (2, 6–
3
11). On the other hand, no structural characterizations by
X-ray absorption (XANES) and X-ray photoelectron
2
X-ray diffraction. Clear and transparent (1ꢀx)TeO2–
xWO glass compositions with 0rxr0:325 were synthe-
3
sized. The color of glasses changes from yellow to light
orange depending on composition. Both the homogeneity
and the chemical concentration of each glass were checked
by electronic microscopy with X-ray analysis. The samples
were not subjected to any annealing processes and were
used as obtained.
1
To whom correspondence should be addressed. Fax: +33-4-67-14-42-
0. E-mail: pcharton@lpmc.univ-montp2.fr.
9
1
75
0022-4596/02 $35.00
r 2002 Elsevier Science (USA)
All rights reserved.

1
76
CHARTON ET AL.
ꢀ
8
White a-TeO (14) and yellow monoclinic g-WO (15) 5 ꢁ 10 Pa. The dispersif hemispheric-type electron analy-
2
3
compounds are commercial powders (Aldrich, Fluka) with zer was set at a band pass energy of 30 eV. In this case, the
a nominal purity of 99.99%. The tungstates of alkali and instrumental resolution taken as the full-width at half-
alkaline earth metals were prepared by solid state reaction maximum (FWHM) of the Ag3d5 photo-peak was 0.75 eV.
of the carbonate Li CO or BaCO (commercial products The C1s peak position corresponding to a hydrocarbon
2
3
3
from Aldrich) with g-WO . White Li W O powder with environment (C–C and C–H bonds) was located at 285 eV.
3
2
2
7
the triclinic symmetry (16) was obtained after 24 h at The insulator samples were put under a secondary electron
7
001C. White BaWO powder with the tetragonal symme- flux of weak energy (6 eV) to compensate the charge effects.
4
try was synthesized at 7551C during 3 days (17). Stoichio- The powdered samples are pressed on an indium foil and a
metric PbO (Fluka) and g-WO mixture was heated up to 2-mm diameter metallic (stainless steel) diaphragm is
3
7
X-ray diffraction was used to confirm the crystallized state was done using the commercial ECLIPSE software. The
501C during 3 days to form b-PbWO stolzite form (18). placed on to favor the charge evacuation. Data processing
4
and the single-phase structure.
photo-peak area was determined after subtraction of the
non-linear spectral background of Shirley type (20). The
spectral simulations were based on a Lorentz (30%)–
Gaussian (70%) profile.
2
.2. Physical Characterizations
Infrared (IR) transmission measurements were made
using a Perkin-Elmer 1600 series FTIR spectrometer from
4
3
. RESULTS
000 to 400 cmꢀ at intervals of 4 cm . Measurements
were carried out on identical KBr pellets.
1
ꢀ1
3
.1. InfraredSpectroscopy
Te LIII edge X-ray absorption near edge structure
XANES) measurements were carried out on the D44
(
The infrared transmission spectra of crystalline com-
beam line of the DCI storage ring at LURE (Orsay) pounds taken as references are given in Fig. 1a. In the
working with an electron energy of 1.85 GeV and an paratellurite a-TeO form, the Te environment consists in
2
average positron current of 250 mA. Room temperature distorted trigonal bipyramids (tbp) TeO E with C point
2
4
2V
(
data were collected in transmission mode using two group (2Te–O =2.12 A, 2Te–O =1.88 A and E=Te 5s
(
ax
eq
ionization chambers filled with He/Ne mixture. A double lone pair (14)). According to Arnaudov et al. (21), the
ꢀ
1
crystal Si(111) monochromator was used to obtain a single sharp band at 770 cm
s
corresponds to the symmetric
beam. The harmonic energies were rejected using a grazing equatorial (n TeO ) vibration, while the broad non-
2
eq
ꢀ
1
incidence mirror (19). The energy steps and the counting symmetric band at 660 cm includes the asymmetric
as
times were adjusted to improve data quality. Samples were equatorial (n TeO ) , the symmetric and asymmetric axial
2
s
eq
as
prepared by grinding and sieving glasses to obtain fine (n TeO ) and (n TeO ) stretching modes of the TeO E
2
ax
2 ax
4
powders with regular grain size of 20 mm. The mass of glass units.
powder has been previously computed to avoid saturation The room-temperature g-WO modification, with P21=n
3
effects and to optimize the signal-to-noise ratio. The space group (15), is composed of corner-sharing WO6
powders were then dispersed in ethanol and settled on a octahedra having large distortion. Its IR spectrum is
microporous membrane to obtain homogenous samples dominated by a strong and large band centered at about
ꢀ
1
ꢀ1
deposits.
850 cm
with two shoulders at 770 and 910 cm .
W LIII and L edges XANES spectra were recorded using Li W O crystallizes in the triclinic space group P ꢀ 1
I
2
2
7
a Si(311) double crystal monochromator with ionization and is built up of largely distorted WO octahedra and
chambers containing argon. The computed mass of glass LiO tetrahedra (16). By sharing edges, the WO octahedra
6
4
6
2
was thoroughly mixed with cellulose used as binder and the form infinite double chains of (W O ) extending along
ꢀ
2
7
mixture was pressed in 10-mm diameter pellet.
To compare the XANES spectra, the absorption back- distorted in Li W O crystalline compound (larger set of
the c-axis. Because the tungsten environment is more
2
2
7
ground subtraction was first carried out using a linear distances than in WO ), we observe more distinctly many
3
function on the pre-edge region and the spectra then bands characterizing the W–O vibrations. This could be
normalized by taking an energy point around 80 eV above explained by a removal of degeneracy for Li W O
7
2
2
the edge.
Measurements of the X-ray photoelectron (XP) core-
compared to WO3.
BaWO (17) and b-PbWO (18) compounds with the
4
4
level spectra were carried out with an ESCALAB-220XL scheelite-like structure belong to the space group I41=a: In
spectrometer. Monochromatic 120 W AlKa X-ray provided these structures, the W atoms are located at the center of
the excitation radiation. Under these conditions, the the isolated regular tetrahedra. Their IR spectra show two
ꢀ
1
irradiated surface was a 500-mm diameter spot. The maxima in the 770–850 cm range which agree well with
working pressure inside the analyzer chamber was about previous works (22).

TeO
2
–WO
3
GLASSES
177
FIG. 1. Infrared spectra of (a) crystallized references and (b) (1ꢀx)TeO
2
–xWO
3
glasses with 0rxr0:325:
IR spectra of (1ꢀx)TeO –xWO3 glass samples with negativity and can therefore substitute for each other in
2
various compositions x; Fig. 1b, consist of major bands in bonding with O atoms (11). That is, there is a small
the 600–800 cmꢀ range and a band around 930 cm . The fraction of W cations which are incorporated in the glass
1
ꢀ1
typical broadening of the vibration bands due to the glassy network.
state is observed. TeO glass (x ¼ 0) IR spectrum is rather
The 930 cmꢀ band and the 870 cmꢀ1 shoulder are
1
2
ꢀ
1
similar to a-TeO data. The 620 cm major band and the directly connected to W–O vibrations since they are
2
ꢀ
1
shoulder at about 770 cm are, respectively, assigned to inactive in the IR spectrum of TeO glass. The 870 cm
ꢀ1
2
symmetrical vibrations of Te–Oax bonds and to symmetric shoulder is assigned to W–O–W vibrations (2, 8, 27).
vibrations of Te–Oeq bonds of TeO E units (23). As the Compared to the tungstate references, Fig. 1a, the
4
ꢀ
1
WO -content increases, Fig. 1b, the major band shifts from 930 cm
3
20 cm (x ¼ 0) to 665 cm (x ¼ 0:325). This may be distorted WO octahedra as encountered in Li W O . On
band may be assigned to the existence of
ꢀ
1
ꢀ1
6
6
2
2
7
related to the apparition of TeO E units concomitant to a the other hand, the IR spectra of K WO and Rb WO
4
3
2
4
2
reduction in the number of TeO E units (24, 25). The crystalline compounds containing slightly distorted tetra-
4
ꢀ
1
70 cm shoulder relative to the existence of TeO E units hedra WO present a weak band at around 925 cm (28).
ꢀ1
7
4
4
Thus, from IR spectroscopy the attribution of the 930 cmꢀ
1
is still present for x ¼ 0:325:
The absorption band at 490 cm
ꢀ
1
which slightly in- band is difficult.
creases in intensity with WO -content is inactive in the IR
3
spectrum of TeO glass (x ¼ 0), Fig. 1b. The appearance of
2
this new band shows the direct influence of the WO oxide
on the tellurite network. It can be assigned to Te–O–W
bridging bonds which would increase the network con-
3
3
.2. Te LIII Edge XANES Spectroscopy
Figure 2a compares the Te LIII edge normalized XANES
nectivity. This assignment is made in agreement with the spectra of (1ꢀx)TeO –xWO glasses of various composi-
2
3
theoretical model for vibrations of mixed bridge bonds tions with the references a-TeO and Tl TeO . This latter
2
2
3
containing heavy metal and glass former atoms (26). Then, contains isolated trigonal pyramid TeO E units with
the formation of Te–O–W bridging bonds is expected regular bond length (29). Tl TeO as powder was kindly
3
2
3
because both W and Te atoms have comparable electro- provided by the SPCTS (Limoges, France).

1
78
CHARTON ET AL.
2 3 2 3 2
FIG. 2. Normalized Te LIII edge XANES spectra of (a) (1ꢀx)TeO –xWO glasses with the references Tl TeO and a-TeO . In (b), zoom of the
pre-edge feature A.
From a general point of view, Te LIII edge XANES data 3.3. X-Ray Photoelectron Spectroscopy (XPS)
report electronic transitions from the inner Te 2p3/2 core
In order to get structural information from XP spectra,
level to the Te empty states of s and d-type (30). The form
we have compared the core binding energies of the glass
and intensity of the XANES features depend mainly on the
samples with those of standard compounds. The core
density of the vacant states and the transition probability
electron binding energy is influenced by the local electron
(
4
31). The spectra exhibit a pre-peak, noted A, around
348 eV, Fig. 2a, characterizing the interactions of the
density surrounding the atom and by the structural
arrangement of the other atoms within the solid. This is
usually referred to as a chemical shift (34). Table 1 reports
both the W4f7/2 and O1s binding energies of glasses and
several references. The experimental binding energies are
determined with an uncertainty of 70.1 eV.
empty Te 5s states localized at the bottom of the
conduction band with the O 2p3/2 orbitals (antibonding
states) (30, 32). Since the absorption spectra are normalized
in the same way, the A pre-peak intensities can be
compared, Fig. 2b. The intensity of the pre-peak A depends
on the coordination number of the tellurium atoms: it is
lower for a-TeO built up from TeO E units compared to
Spectra of the W4f energy region of (1ꢀx)TeO –xWO
2
3
glass compositions with x ¼ 0:05 and 0.30 and crystallized
2
4
Tl TeO based on pyramidal TeO E groups. The same
2
3
3
evolution is registered for the resonance feature called B,
Fig. 2a, related to the local order around Te atoms (33).
The intensity of both the A pre-peak and the feature B
TABLE 1
Peak’s Position Usedby Bigey et al. for the Fitting Procedure
of XPS Spectra (36)
increases gradually from TeO glass (x ¼ 0) to x ¼ 0:30
2
glass composition, see Figs. 2a and 2b. These increases
reveal a continuous change of tellurium atom environment
when the WO3 content increases. From the direct
comparison with the crystallized references, it appears that
some Te atom sites in (1ꢀx)TeO –xWO glasses change
Binding energies of
W 4f7/2 state (eV)
Oxidation states of tungsten
6+
5+
4+
0
W
W
W
W
35.5
34.5
32.7
31.2
2
3
progressively from TeO E (a-TeO ) to TeO E (Tl TeO )
4
2
3
2
3
units.

TeO
2
–WO
3
GLASSES
179
TABLE 2
Bigey et al. (36) (Table 1), constitutes the only oxidation
state present in the glasses whatever the composition.
O1s andW4 f Binding Energies and Full-Widths at Half-
Maximum FWHM (in Parentheses) for Some Glass Composi-
tions andSeveral References
5+
Moreover, no signal corresponding to W oxidation state
was detected by EPR spectroscopy. The W4f7/2 binding
energy registered for the glasses is closer to that found in g-
WO (WO units) than in b-PbWO (WO units), Table 2.
Sample
a-TeO
g-WO
b-PbWO
TeO
O1s (eV)
W4f7/2 (eV)
3
6
4
4
2
530.6
Figure 3b shows O1s core-level photoelectron spectra
obtained for various glasses and crystallized references. For
the crystallized references, the O1s peaks consist of only a
single and symmetric Gaussian–Lorentzian peak with a
small FWHM E1.2 eV. For (1ꢀx)TeO –xWO glasses
(
1.2)
530.7
1.2)
530.7
1.1)
530.4
(1.50)
3
35.8
(1.0)
35.4
(1.0)
(
4
(
2
3
2
with x ¼ 0:05 and 0.30, the registered FWHM of the only
one component O1s peak is slightly larger, E1.5 eV, and is
independent of glass compositions, Table 1. Himei et al.
(37) registered the O1s binding energies of two references
a-TeO2 (Te–O–Te bridging oxygen atoms, BO) and
(x ¼ 0)
35.8
(1.2)
0.95TeO –0.05WO
2
3
530.8
(1.5)
530.7
(1.4)
(
x ¼ 0:05)
.70TeO –0.30WO
x ¼ 0:30)
0
2
3
35.7
(1.1)
(
ꢀ
+
Li TeO (Te–O y Li non-bridging oxygen atoms,
2
3
NBO). The difference of the O1s binding energy between
references b-PbWO and g-WO are presented in Fig. 3a in BO (a-TeO , 530.5 eV) and NBO (Li TeO , 529.6 eV) is
4
3
2
2
3
terms of the W4f7/2-4f5/2 spin-orbit components. The sufficiently large (0.9 eV) to be registered at least as an
important information deduced from this analysis concerns asymmetry of the O1s peak and an increase of the FWHM
the valence state of the W ions in the glasses. Indeed, a (37, 38).
large chemical shift is observed for W atoms with 0, +4,
+
The O1s binding energies found for the glass samples are
5 and +6 formal oxidation states (36–35), Table 1. The assigned to the existence of bridging oxygen atoms X–O–X
6
+
spectra reveal that W , characterized by a W4f7/2 binding (X=Te, W) as found in the registered references, Table 1.
energy at 35.670.2 eV (35) similar to this published by Furthermore, the absence of both an asymmetry on the
FIG. 3. X-ray photoelectron spectra of (a) the W4f region and (b) the O1s core-level photoelectron peak of x ¼ 0:05 and 0.30 glass compositions
compared with several references.

1
80
CHARTON ET AL.
lower energy side of the O1s peak and a shift of the O1s to the increase of distortion of WO octahedra (40). The
6
peak toward smaller binding energy with increase in the sharp, fairly intense post-edge feature B registered only for
WO content, Fig. 3b, might indicate that oxygen atoms in BaWO spectrum is characteristic of WO tetrahedra.
3
4
4
(
1ꢀx)TeO –xWO glasses with 0:0rxr0:325 are present
Normalized W LIII edge XANES spectra of (1ꢀx)TeO2–
2
3
only as BO atoms. The shift to higher energy, Table 1, of xWO glasses with 0:10rxr0:30 are presented in Fig. 4b.
3
the O1s binding energy in the glasses from x ¼ 0 (530.4 eV) The shape of the absorption spectra undergoes no
to x ¼ 0:05 (530.8 eV) and x ¼ 0:30 (530.7 eV) could be considerable changes with x: The absence of a post-edge
explained by a difference in the local electron density feature B, as encountered in BaWO , shows that the W
surrounding the oxygen atoms. TeO glass (x ¼ 0) would environment in the glasses consists only in WO octahedra.
4
2
6
contain di-coordinated bridging oxygen atoms forming Furthermore, the significant decrease of the amplitude of
Te–O–Te linkages as in a-TeO , while x ¼ 0:05 and 0.30 the WL registered from x ¼ 0:10 to 0.30 suggests an
2
glasses would form Te–O–Te, Te–O–W and W–O–W increase of the WO octahedra distortion with the WO -
6
3
linkages.
.4. W LIII andL Edges XANES Spectroscopy
content.
We present in Fig. 5a the normalized XANES regions
registered at W LI edge for three references, g-WO3,
Li W O and BaWO . The intensity of the pre-edge feature
3
I
2
2
7
4
Figure 4a shows the normalized W LIII edge XANES A observed in W L edge XANES spectra is determined
I
signals of crystalline compounds taken as references. The primarily by the site symmetry of the transition-metal ion.
so-called ‘‘white line’’ (WL) resonance, labeled A, corre- Indeed, the electronic transition 2s(W)-5d(W)+2p(O) is
sponds to the dipole-allowed transition from the 2p3/2(W) dipole forbidden in the case of regular octahedra (inversion
core level to a quasi-bound 5d(W)+2p(O) mixed-state (39). center), but is allowed for distorted octahedra and
The amplitude of the WL is larger in g-WO reference tetrahedra (39, 41). The amplitude of the pre-edge feature
3
compared to Li W O , both structures are built up with A is the largest in the case of W tetrahedral coordination
distorted WO octahedra. In stoichiometric g-WO and (BaWO ) and is registered as a weak shoulder for distorted
2
2
7
6
3
4
Li W O , the tungsten ions have the valence state 6+ with W octahedra (g-WO3 and Li W O ). Furthermore, its
2
2
7
2
2
7
an empty 5d shell. The decrease of the WL intensity is due amplitude depends on the degree of WO6 octahedra
FIG. 4. Normalized W LIII edge XANES spectra of (a) the crystallized references BaWO
glasses.
4 3 2 2 7 2 3
, g-WO and Li W O and of (b) (1ꢀx)TeO –xWO

TeO
2
–WO
3
GLASSES
181
FIG. 5. Normalized W L
I
edge XANES spectra of (a) the crystallized references BaWO
4
, g-WO
3
and Li
2
2
W O
7
and of (b) (1ꢀx)TeO
2
–xWO
3
glasses.
distortion. Indeed, the distortion of the octahedra facil- regular evolution of their shape with x in accordance with
itates d2p orbital mixing, and thus enhances the pre-edge the Tg evolution. The analysis of these IR data shows the
feature A amplitude (40). The pre-edge feature A has the formation of Te–O–W linkages that contribute to the Tg
largest amplitude in Li W O compared to g-WO refer- increases (9) and an evolution of the Te surrounding.
2
2
7
3
ence in accordance with the increase of the average W–O Indeed, the trigonal bipyramid TeO E units forming TeO
(
4
2
bond length from 1.926 to 1.955 A. The edge feature, (x ¼ 0) glass are the major components of the glass
labeled B, is the allowed dipole transition 2s(W)- network. However, for high WO content, some of these
3
6
p(W)+2p(O) (40).
Normalized W L edge XANES spectra of (1ꢀx)TeO –
TeO E units are converted in trigonal pyramids TeO E.
4 3
The existence of a mixed Te environment (TeO /TeO )
4 3
I
2
xWO with 0.10rxr0.30 are presented in Fig. 5b. The for glasses with high WO content is also pointed out by Te
3
3
shape of the absorption spectra undergoes no considerable LIII XANES spectroscopy. The main XANES feature
changes with x and present close similitude with the registered for (1ꢀx)TeO –xWO glasses, Fig. 2b, is the pre-
2
3
spectrum of the reference g-WO . The pre-edge feature A is peak, A, which corresponds to the 2p-5s(Te) transition.
3
present as a shoulder indicating the presence of distorted The regular evolution in the intensity of this pre-peak with
WO octahedra site in these glasses as pointed out by the W x may also be related to the stereochemical activity of the
6
2
lone pair 5s (Te) (32, 42), that directly depends on the
tellurium coordination number. The stereochemical activ-
2
ity of the lone pair 5s (Te) is maximum in the reference
LIII edge XANES analysis.
4. DISCUSSION
Tl TeO made up of TeO E trigonal pyramids. Thus, the
2
3
3
The glass transition temperatures, Tg, registered for registered evolution of the Te LIII XANES spectra with the
glasses obtained in the TeO –WO system increase WO3 content indicates a progressive transformation of
regularly with the WO content (1, 5). This compositional some Te polyhedra from TeO E units to more regular
2
3
3
4
dependence of Tg can reveal a transformation of the glass TeO E units.
3
structure referred to the increase in the network connectiv- This result concerning the structural evolution of the
ity. The presence of tungsten atoms would lead to a tellurium polyhedra in function of the composition is
densification of the TeO glass matrix. The IR curves of the consistent with other works using Raman spectroscopy
2
(
1ꢀx)TeO –xWO glasses with 0rxr0:325 clearly show a (8, 10). On the other hand, most of the papers describing
2
3

1
82
CHARTON ET AL.
IR and Raman data on these tungsten oxide–tellurite assigned to the existence of bridging oxygen atoms X–O–X
glasses assumed that Te is only present as TeO E units (X=Te, W). However, the existence of TeO E trigonal
4
3
whatever the composition (2, 7, 11). Indeed, the TeO E- pyramids with three bridging oxygen atoms brings a local
4
TeO E transformation is not clearly observed on Raman positive charge which has to be compensated. The local
3
spectra, the Te–O bands appearing at the same range as electrostatic neutrality of the TeO E units could be
3
W–O vibrations.
Now concerning the W
respected with the formation of a Te–O terminal bond
ion coordination state in with double bond character (Te ¼ O). The electronic
6
+
TeO –WO glasses, a large credit is given, in the literature, density surrounding Te ¼ O oxygen atoms is relative close
2
3
either to the presence of only WO tetrahedra (2, 11) or to to BO atoms. Considering the small Te ¼ O proportion, the
4
the existence of a mixed W coordination state made of contribution of such terminal bonds cannot be distin-
WO4 tetrahedra and WO6 octahedra (4, 7, 8, 10). Few guished from other oxygen atoms.
papers report on the existence of tungsten ions in six-
coordination whatever the glass composition (9).
5
. CONCLUSION
As pointed out in our IR study, the presence of the band
centered at 930 cmꢀ attributed to W–O vibration is
difficult to interpret in terms of WO or WO polyhedra.
1
Transparent and stable glasses were obtained in the
TeO –WO system. Their short range order was ap-
proached using several complementary techniques. Infra-
red and Te LIII XANES spectroscopies pointed out the
evolution of the Te environment in function of the glass
composition. The trigonal bipyramids TeO E are the main
4
structural constituents of these glasses. Therefore, when the
WO content increases, some trigonal pyramids TeO E are
formed. Also, some W atoms are incorporated into the
glass network to form Te–O–W linkages.
We were very concerned by the oxidation state and the
coordination state of the tungsten atoms. For the first time,
a precise determination of the W environment in TeO –
4
6
2
3
It is why we have undertaken an X-ray absorption
spectroscopy study at the W LIII and L edges. Indeed,
I
XANES spectroscopy is a powerful tool to provide
information on the local symmetry and coordination
around a given element. Since W LIII and L edges XANES
I
features are sensitive to both the W oxidation state and the
site geometry, we performed XPS analyses on TeO –WO
3
3
2
3
glasses to identify the W oxidation state. Indeed, tungsten
oxide is one of the transition metal oxides which have two
5
+
6+
and W . It is
different oxidation states, namely W
known that in tungsten glasses the electric conduction
arises from electron hopping between these two oxidation
states (43, 44).
Spectra of the W4f energy region of (1ꢀx)TeO –xWO
glass compositions with x ¼ 0:05 and 0.30 reveal that W
2
6
+
WO glasses was realized by XANES spectroscopy. W
3
ions are in six-fold coordination state whatever the glass
composition. These WO octahedra present high distortion
that increases with the WO content, i.e., with the glass
2
3
+
6
6
3
constitutes the only oxidation state present in the glasses
whatever the composition. Based on this result, the
network deformation.
registered features on the W LIII and L edges XANES
I
spectra were analyzed. Both W L and L XANES studies
III
I
6
+
agree with the existence of W ions in six-fold coordina-
tion whatever the glass composition in agreement with (9).
REFERENCES
6
+
2ꢀ
6+
The radius ratio of W to O indicates that W prefers
six-coordination (9). Furthermore, the distortion of the
WO octahedra increases with the WO content and thus,
1
2
3
4
5
6
7
8
9
. T. Kosuge, Y. Benino, V. Dimitrov, R. Sato, and T. Komatsu, J.
Non-Cryst. Solids 242, 154 (1998).
. I. Shaltout, Y. Tang, R. Braunstein, and E. E. Shaisha, J. Phys. Chem.
Solids 57, 1223 (1996).
6
3
with the formation of TeO E entities. The high distortion
3
. S. K. J. Al-Ani, C. A. Hogarth, and R. A. El-Malawany, J. Mater.
Sci. 20, 661 (1985).
of the WO octahedra seems to be responsible for the
6
ꢀ
1
ꢀ1
formation of the 930 cm IR band. This 930 cm band is
present as a sharp peak on Raman spectra and its intensity
increases with the WO content (9), i.e., with the WO
. V. Kozhukharov, M. Marinov, and G. Grigorova, J. Non-Cryst.
Solids 28, 429 (1978).
. S. Blanchandin, P. Marchet, P. Thomas, J.-C. Champarnaud-
Mesjard, B. Frit, and A. Chagraoui, J. Mater. Sci. 34, 4285 (1999).
. V. Kozhukharov, S. Neov, I. Gerasimova, and P. Mikula, J. Mater.
Sci. 21, 1707 (1986).
3
6
distortion. The WO octahedra deformation could be to
6
such a degree, that the W atoms may be located in a more
or less off-centered position in octahedral site as in the
crystal chemistry of tungstates. Then, the distinction
between WO and WO units becomes impossible with
. V. Dimitrov, M. Arnaudov, and Y. Dimitriev, Monatsh. Chem. 115,
987 (1984).
. M. Tatsumisago, T. Minami, Y. Kowada, and H. Adachi, Phys.
Chem. Glasses 35, 89 (1994).
. T. Sekiya, N. Mochida, and S. Ogawa, J. Non-Cryst. Solids 176, 105
6
4
this single vibrationnal band.
+
ꢀ
The formation of X y O–Te non-bridging oxygen
atoms is not expected in the TeO –WO glasses. The O1s
binding energies found for the glass samples could be
(1994).
10. B. V. R. Chowdari and P. Pramoda Kumari, Mater. Res. Bul. 34, 327
(1999).
2
3

TeO
2
–WO
3
GLASSES
183
1
1
1
1. I. Shaltout, Y. Tang, R. Braunstein, and A. M. Abu-Elazm, J. Phys. 29. B. Frit, D. Mercurio, P. Thomas, and J.-C. Champarnaud-Mesjard,
Chem. Solids 56, 141 (1995). Z. Kristallogr. NCS 214, 439 (1999).
2. S.-H. Kim, T. Yoko, and S Sakka, J. Am. Ceram. Soc. 76(10), 2486 30. P.-E. Lippens, J. Olivier-Fourcade, J.-C. Jumas, A. Gheorghiu,
1993).
S. Dupont, and C. S e! n e! maud, Phys. Rev. B 56, 13057 (1977).
3. S. Blanchardin, P. Marchet, P. Thomas, J. C. Champarnaud-Mesjard, 31. M. Marezio and J. P. Remeika, J. Chem. Phys. 46, 1862 (1967).
(
B. Frit, and A. Chagraoui, J. Mater. Sci. 34, 4285 (1999).
4. P. A. Thomas, J. Phys. C 21, 4611 (1988).
32. J.-C. Sabadel, P. Armand , P.-E. Lippens, D. Cachau-Hereillat, and
E. Philippot, J. Non-Cryst. Solids 244, 143 (1999).
33. A. Ibanez, T. Ericsson, O. Lindqvist, D. Bazin, and E. Philippot,
J. Mater. Chem. 4, 101 (1994).
1
1
1
5. B. O. Loopstra and P. Boldrini, Acta Crystallogr. 21, 158 (1966).
6. K. Okada, H. Morikawa, F. Marumo, and S. Iwai, Acta Crystallogr.
B 31, 1451 (1975).
34. G. E. McGuire, G. K. Schweitzer, and T. A. Carlson, Inorg. Chem.
12, 2450 (1973).
35. R. J. Colton and J. W. Rabalais, Inorg. Chem. 15, 236 (1976).
1
1
1
7. E. G u. rmen, E. Daniels, and J. S. King, J. Chem. Phys. 55, 1093
(1971).
8. J. M. Moreau, Ph. Galez, J. P. Peigneux, and M. V. Korzhik, J. 36. C. Bigey, V. Logie, A. Bensaddik, J. L. Schmitt, and G. Maire,
Alloys Compd. 238, 46 (1996). J. Phys. IV France 8, Pr5-553 (1998).
9. P. Sainctavit, J. Petiau, A. Manceau, R. Rivallant, M. Belakhovsky, 37. Y. Himei, Y. Miura, T. Nanba, and A. Osaka, J. Non-Cryst. Solids
and G. Renaud, Nucl. Instrum. Methods 273, 423 (1988).
0. D. A. Shirley, Phys. Rev. B 5, 4709 (1972).
211, 64 (1997).
38. Y. Miura, H. Kusano, T. Nanba, and S. Matsumoto, J. Non-Cryst.
Solids 290, 1 (2001).
2
2
1. M. Arnaudov, V. Dimitrov, Y. Dimitriev, and L. Markova, Mater.
Res. Bull. 17, 1121 (1982).
39. A. Kuzmin and J. Purans, J. Phys. IV France 7, C2-971 (1997).
40. A. Balerna, E. Bernieri, E. Burattini, A. Kuzmin, A. Lusis, J. Purans,
and P. Cikmach, Nucl. Inst. Methods Phys. Res. A 308, 240 (1991).
41. J. A. Horsley, I. E. Wachs, J. M. Brown, G. H. Via, and F. D.
Hardcastle, J. Phys. Chem. 91, 4014 (1987).
2
2. G. M. Clark and W. P. Doyle, Spectrochim. Acta 22, 1441 (1966).
3. T.Yoko, K. Kamiya, K. Tanaka, H. Yamada, and S. Sakka,
Nippon Seram. Kyo. Gakuj. Ronb. 97, 289 (1989).
2
2
2
2
4. Y. Dimitriev, V. Y. Dimitrov, V. Dimitrov, and M. Arnaudov,
J. Mater. Sci. 18, 1353 (1983).
5. Y. Mizuno, M. Ikeda, and A. Yoshida, J. Mater. Sci. Lett. 11, 1653
42. J. Olivier-Fourcade, A. Ibanez, J.-C. Jumas, H. Dexpert, C. Blancard,
J.-M. Esteva, and R. C. Karnatak, Eur. J. SolidState Inorg. Chem.
28, 409 (1991).
(1992).
6. A. Miller, K. Nassau, K. Lyons, and M. Lines, J. Non-Cryst. Solids 43. A. A. Bahgat, M. M. El-Samanoudy, and A. I. Sabry, J. Phys.
Chem. Solids 60, 1921 (1999).
99, 289 (1988).
2
7. S. Muthupari and K. J. Rao, J. Phys. Chem. Solids 57, 553 (1996).
8. P. Caillet and P. Saumagne, J. Mol. Structure 4, 191 (1969).
44. C. A. Hogarth and E. Assadzadeh-Kashani, J. Mater. Sci. 18,
1255 (1983).
2