Full text of DOI:10.1557/JMR.2000.0035

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Structural and physical properties of Fe2O3-doped lead
vanadate glass
S. Mandala) and S. Hazrab)
Department of Solid State Physics, Indian Association for the Cultivation of Science, Jadavpur,
Calcutta 700032, India
(Received 24 February 1998; accepted 15 October 1999)
The role of Fe2O3 in the structural and physical properties of ternary lead
vanadium iron glass system has been studied in comparison with the binary
lead vanadate glasses. X-ray diffraction, scanning electron microscopy, and
differential thermal analysis show that homogeneous glasses of composition
10Fe2O3 и xV2O5 и (90 − x)PbO can be obtained for x ס 50 to 80 mol%. Observation
from the infrared spectroscopy shows that the basic building blocks of these glasses
are same as those of crystalline V2O5, while differential thermal analysis and electrical
conduction of these glasses suggest that there is a strong role of iron, both in the glass
network and in the conduction mechanism for the glasses containing a low percentage
of vanadium.
I. INTRODUCTION
II. EXPERIMENT
Oxide glasses containing transition metal ions are of
great interest because of their possible application in the
field of optical switching and memory switching de-
vices.1,2 They show semiconducting properties due to the
presence of two different valence states of the transition
metal ions. Glasses containing vanadium are of particular
interest since vanadium itself forms the glassy network
and hence a large amount of vanadium can be incor-
porated. The glasses containing vanadium are highly
conductive, which makes them more suitable for appli-
cations in electrical switching devices. Some work on the
vanadate glasses has been done recently3–5 in which va-
nadium oxide plays the unique role of network former.
Recently, we have studied some structural5 and electrical
properties6 of the lead vanadate glass system.
In the present work, iron oxide was used to dope the
lead vanadate glasses in a fixed proportion, and the role
of iron on the structural and electrical properties of the
prepared glass samples was studied in comparison with
the lead vanadium glasses with the change of glass com-
position. It was attempted to correlate the results from the
structural studies with the results of the electrical studies.
Glass samples of compositions 10Fe2O3 и xV2O5 и (90 −
x)PbO with x ס 50 to 80 mol% have been prepared from
reagent grade chemicals V2O5, PbO, and Fe2O3. The
chemicals mixed in desired proportions were melted in
pure alumina crucibles. The melts were kept for 1 h in the
temperature range 900–1000 °C depending on the glass
composition for homogeneous mixing. The vitrification
was achieved by subsequent rapid cooling of the melts
between two brass plates. Chemical analyses were done
to find out any trace of aluminum in the glass samples.
The results, however, were negative.
The x-ray diffraction patterns of the as-prepared and of
the heat-treated samples were taken in a Philips x-ray
diffractometer (model PW 1050/51). The scanning elec-
tron microscopy of the polished surface of the as-
prepared and heat-treated samples were taken in a
Hitachi scanning electron microscope (model S-200).
The differential thermal analysis (DTA) of the powdered
samples was carried out in air in a Shimadzu thermal
analyzer (model DT-40). The infrared (IR) spectra of
the powdered samples and of the starting materials in
KBr matrices were taken in a Perkin-Elmer spectro-
photometer (model 783) in the wavenumber range 200–
4000 cm−1. A 200-Å-thick gold coating was deposited as
electrode material on both surfaces of the samples by
vacuum evaporation. The electrical measurements of the
samples were carried out by using a Keithley electrom-
eter (model 617) in the temperature range 100–450 K in
dry conditions.
a)Present address: Depto. Solidos Ionicos, Instituto de Ciencia de
Materiales de Madrid, Consejo Superior de Investigaciones Ci-
entificas, Cantoblanco, 28049-Madrid, Spain.
b)Present address: Surface Physics Division, Saha Institute of
Nuclear Physics, Sector 1, Block-AFЈ, Bidhannagar, Calcutta
700064, India.
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S. Mandal et al.: Structural and physical properties of Fe2O3-doped lead vanadate glass
III. RESULTS AND DISCUSSION
A. Glass formation domain
x)PbO were obtained for x ס 50 to 80 mol%, which
represents the homogeneous glass formation domain for
the present system.
X-ray diffraction patterns (not shown here) of the
glassy samples show broad diffuse scattering at low
angles which confirm the amorphous nature of the
samples. The scanning electron micrograph of as-
prepared samples, shown in Fig. 1(a), shows no sign of
microstructure, confirming the amorphous and homoge-
neous nature of the samples. However, the micrograph
[Fig. 1(b)] of the samples heat treated near the crystalli-
zation temperature shows the distinct presence of a mi-
crostructure at the surface of the samples. Differential
thermal analysis curves for two glass compositions are
shown in Fig. 2, which exhibit an endothermic peak due
to the glass transition followed by a prominent exother-
mic peak due to crystallization. Similar observations for
the samples of composition 10Fe2O3 и xV2O5 и (90 −
B. Glass network and structure
The glass transition (Tg) and crystallization (Tc) tem-
perature were estimated within an error of ±5 °C and are
shown in Table I. The variations of Tg with glass com-
positions are shown in the inset of Fig. 2. The Tg of
binary lead vanadate glasses are also included for com-
parison. It can be noted that in the ternary glasses the
change of Tg is more rapid than in the binary glasses. The
TABLE I. Parameter obtained by fitting Schnakenberg’s model to the
experimental conductivity data of the ternary glasses along with Tg
and Tc.
Glass compositions (mol%)
WH
Wd
␯
Tg
Tc
0
V2O5
PbO
(eV) (eV) (1013 s−1
)
(°C) (°C)
50
60
70
80
40
30
20
10
0.47
0.43
0.43
0.39
0.28
0.27
0.27
0.20
1.7
1.8
1.9
1.6
310
300
255
255
390
360
350
340
FIG. 2. Differential thermal analysis curves of (a) 80 mol% V2O5 and
(b) 50 mol% V2O5 glass compositions of the ternary glasses. The inset
shows the variation of glass transition temperature (Tg) with the varia-
tion of mol% V2O5 for ternary vanadate glasses along with the binary
lead vanadate glasses.
FIG. 1. Scanning electron micrographs of (a) as-prepared 50 mol%
V2O5 and (b) heat-treated 80 mol% V2O5 glass compositions.
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S. Mandal et al.: Structural and physical properties of Fe2O3-doped lead vanadate glass
Tg for ternary glasses containing 50 and 60 mol% V2O5
Pb2+ has a direct influence on the isolated VסO bonds
leading to a drop in wavenumber. This is more pro-
nounced in the glass composition where the percentage
of PbO is greater [Fig. 3(f) and 3(g)]. This shows that the
basic network building block in the glasses remain the
same as in crystalline V2O5. The weakness of the bands
appears due to the randomness in the structure of the
materials.
are 310 and 300 °C, while for those containing 70 and
80 mol% V2O5, Tg is 255 °C. Such a large change
( 45 °C) in Tg with composition cannot be accounted for
the formation of nonbridging oxygen in the glass net-
work. This can only happen if some of the iron goes into
the V–O–V chain leading to a V–O–Fe chain which will
strengthen the network leading to an increase in Tg. This
is a marked difference of this system with the binary lead
vanadate system.
C. Electrical conductivity
The infrared spectra at room temprature of all the
glasses are shown in Fig. 3. IR spectra of the crystal-
line V2O5, PbO, and Fe2O3 are also included in the
figure [3(a)–3(c)] for comparison. In the IR spectra a
water band at 3400 cm−1 and an –OH stretching band
at 2920 cm−1 have been observed. Another band at
1640 cm−1 is also observed which may be due to the –OH
bending mode of absorbed water. These bands are due to
the hygroscopic character of the powdered samples.
However, the bulk glass samples are very stable and not
hygroscopic in nature. An intense high-frequency band at
1020 cm−1 has been observed for crystalline V2O5. This
band is assigned to the vibrations of isolated VסO
vanadyl groups in V2O5 trigonal bipyramids.6 In the
glass samples this band becomes weak and a shoulder.
This weak band shifts toward the low-frequency region
(950–980 cm−1) with the increase of PbO content. Ac-
cording to the mechanism suggested earlier,8 the Pb2+
ions occupy a position between the V–O–V layers. Thus
The temperature dependence of the logarithmic con-
ductivity is shown in Fig. 4 as a function of reciprocal
temperature for three glass compositions. The inset of
Fig. 4 shows the conductivity at 300 K with the change
of composition for both the ternary and binary glasses.
The conductivities were measured within an error of
5–10%. The sublinear change in conductivity with recip-
rocal temperature indicates a temperature-dependent ac-
tivation energy, characteristic of small-polaron-hopping
conduction,9 which is confirmed later in the text. It is
clear from the inset of Fig. 4 that for higher V2O5 content
glasses the conductivity is higher in both the glass sys-
tems. The conductivity of the two systems is almost the
same for the glasses containing 80 and 70 mol% V2O5,
which indicates that the conduction of these glasses is
due to hopping of charge carriers between two vanadium
states only. But as is evident from the other composi-
tions, this is not true. The ternary glasses have a higher
conductivity over their binary counterpart. We propose
FIG. 4. Dependence of the logarithmic conductivity is shown as a
function of reciprocal temperature for three glass compositions, (᭿)
80 mol% V2O5, (᭹) 70 mol% V2O5, and (᭡) 50 mol% V2O5. The
solid line is the best fit to Schnakenberg’s generalized polaron-
hopping model. The inset shows the conductivity at 300 K with the
change of composition for both the ternary and binary glasses.
FIG. 3. Room-temperature infrared spectra of the ternary glasses.
The spectra of starting materials are also included for comparison:
(a) crystalline V2O5, (b) crystalline PbO, (c) crystalline Fe2O3, (d)
80 mol% V2O5, (e) 70 mol% V2O5, (f) 60 mol% V2O5, (g) 50 mol%
V2O5.
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S. Mandal et al.: Structural and physical properties of Fe2O3-doped lead vanadate glass
that iron also takes part in the conduction mechanism
the ternary lead vanadium iron glasses have been done to
see the effect of iron in the structure of the glasses. The
study reveals that it is possible to prepare a wide com-
position range of glasses. It was seen that while only
vanadium take part in the conduction mechanism for the
two highest V2O5 content glasses, in the other two glass
compositions both vanadium and iron took part in the
conduction mechanism. This is due to the fact that a
chain like V–O–Fe is formed along with V–O–V, which
is also confirmed from the DTA study.
giving a higher conductivity, since we have earlier seen
in the DTA; the most probable case here is the formation
of a V–O–Fe bridge so that hopping of polaron from the
vanadium site to the iron site and vice versa take place.
To account for the conductivity in a wide temperature
range Schnakenberg10 has considered a general polaron-
hopping model in which an optical multiphonon process
determines the conductivity at higher temperature, while
at low temperatures charge carrier transport is an acous-
tical one-phonon-assisted hopping process. The tem-
perature dependence of the conductivity in this model
has the form
ACKNOWLEDGMENTS
−1[sinh(h␯0/kBT)]1/2 exp[−(4WH /h␯0)
tanh(h␯0/4kBT)] exp(−WD/kBT)
The authors acknowledge financial support from the
University Grants Commission of India. The authors are
also grateful to Dr. A. Ghosh for his valuable suggestions
in this investigation.
␴
T
,
where WH is the polaron hopping energy, WD is the dis-
order energy resulting from the variation of local envi-
ronment of ions, and ␯0 is the optical phonon frequency.
This model predicts a temperature-dependent hopping
energy which decreases with the decrease of temperature
consistent with the data presented in Fig. 4. The experi-
mental data were fitted with the theory, and the best fit is
shown in Fig. 4. The best fit values of the parameters ␯0,
WH, and WD are shown in Table I. The WD values show
that disorderliness is greatest for 50 mol% V2O5 glass
composition.
REFERENCES
1. Y. Sakuri and J. Yamaki, J. Electrochem. Soc. 132, 512 (1985).
2. J. Livage, J.P. Jolivet, and E. Tronc, J. Non-Cryst. Solids 121, 35
(1990).
3. V. Fares, M. Magini, and A. Montero, J. Non-Cryst. Solids 99,
404 (1988).
4. V. Dimitrov and Y. Dimitriev, J. Non-Cryst. Solids 122, 133
(1990).
5. S. Mandal and A. Ghosh, Phys. Rev. B 48, 9388 (1993).
6. S. Mandal and A. Ghosh, Phys. Rev. B 49, 3131 (1994).
7. E. Dachille and R. Roy, J. Am. Ceram. Soc. 42, 78 (1965).
8. Y. Dimitriev, V. Dimitrov, M. Arnaudov, and D. Topalov, J. Non-
Cryst. Solids 57, 147 (1983).
IV. CONCLUSION
Various investigations such as x-ray diffraction, scan-
ning electron microscopy, differential thermal analysis,
infrared spectroscopy, and electrical conductivity of
9. I.G. Austin and N.F. Mott, Adv. Phys. 18, 41 (1969).
10. J. Schnakenberg, Phys. Status Solidi 28, 623 (1968).
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