It is becoming increasingly important to understand the mechanical properties
of glasses in addition to their other physical properties from the point of
view of basic physics as well as applications. From a study of the structure
property relationship of binary glasses it is found that they may be divided
into two categories, as normal and anomalous, depending upon whether a particular
property changes continuously with composition or suffers a discontinues change
at some composition. Furthermore, one more recent investigation (Paul
et al., 1997) of vanadium glasses indicates that they belong to the
normal category. The mechanical behaviour of these two component (binary) glasses
has been more or less well understood in terms of existing models. In comparison,
the ternary glasses seem to have received less attention. The data on these
glasses are also meager to test the existing ideas which have been found to
be useful in analysing the physical process in the two component binary glasses.
In the present study, we have investigated the acoustic properties of two ternary
vanadium glass systems such as (I) Na2CO3 -V2O5-P2O5
(VSP Glass) and (II) P2O5 - V2O5-MnO2
(VPM Glass). Vanadium pentoxide is one of the transition metals and it exhibits
semi-conducting properties and whose electrical conductivity lies between V5+
and V4+ of vandadium ions (Seshasayee and Muruganandam,
2006). Such a semi-conductivity behaviour of V2O5
is purely owing to its two valence V5+ and V4+ state of
vanadium (Mott, 1968). This oxide metal has been categorized
as a well-reformed glass former and can posses the same network either as a
network former or as a network modifier owing to its concentration.
Much work has been made on glass system containing with MnO2 and
Na2CO3, other than vanadium glass are abundant but the
above components doped with vanadium are very few. In the present work, efforts
are made to study the effects of structural and physical properties of the vanadium
glasses with MnO2 and Na2CO3 with the exposure
to ultrasonic studies, X-Ray Diffraction studies (XRD) Fourier Transformation
Infrared Spectroscopy (FTIR) studies and Scanning Electron Microscopic (SEM)
MATERIALS AND METHODS
Preparation of glass samples: The chemicals used in the present research
work were Analytical Reagent (AR) and Spectroscopic Reagent (SR) grade with
minimum assay 99% were obtained from Sd fine chemicals India and E-Merck, Germany.
The composition was prepared in mole percentage (mol%) with decreasing content
of P2O5 and MnO2 with that of V2O5
in VSP and VPM glass system, respectively are depicted in Table
1. Further, all the chemicals were handled in an precautionary manner as
The required amounts (approximately 20 g) in mol% (mole percentage) of required
chemicals in powder form were weighed using single pan digital balance (Model
SHIMADZU AX 200, Japan make) having an accuracy of 0.0001 g. The homogenization
of the appropriate mixture of the component of chemicals was effected by repeating
grinding using a pestle and mortar. The homogeneous mixture was put in a silica
crucible and placed in an electrical furnace. Melting was carried out under
controlled conditions with occasional stirring.
||Composition of glasses
The temperature controlled muffle furnace was gradually raised to a higher
temperature at the rate of 100 K h-1 and a glassily structure was
noticed for VSP glass system at 1020 K and for VPM glass system 1060 K, respectively
and eventually the molten glass melt was immediately poured on a heavy copper
molding block having the dimension of 12 mm diameter and 6 mm length kept at
room temperature. Then the glass samples were annealed at 400 K for 2 h to avoid
the mechanical strains developed during the quenching process. The two opposite
faces of glass ware highly polished to ensure a good parallelism. All glasses
are cleaned with acetone to remove the presences of any foreign particles. The
samples are prepared chemically stable and non-hygroscopic and such glass samples,
are shown in Fig. 1a VSP glass samples (system 1) and 1b VPM
glass samples (system 2).
Measurement of ultrasonic velocities: The ultrasonic longitudinal (UL)
and shear velocities (US) of the specimen were determined by using
pulse-echo methods at room temperature at 5 MHz using X-cut and Y-cut transducers.
These transducers act as both transmitters and receivers of the ultrasonic pulse.
The transducers were brought into contact with each of the twelve samples by
means of a couplant, in order to ensure that there was no air void between the
transducer and the specimen. Couplant D-Gel type was used for longitudinal waves
while resin was used for shear waves. By applying constant pressure on the probe
the echo waveforms were obtained on the display unit and stored in the memory.
Figure 2a shows one such echo waveforms obtained for longitudinal
and shear waves of system 1 and Fig. 2b represents the same
for system 2.
Measurement of density: The density of the glass samples was measured
using relative measurement technique. Benzene was used as a buoyant liquid.
The glass samples were weighed both in air and after immersing in benzene
at 303 K. The weight of the glass samples was measured in a single pan with
an accuracy of 0.000 kg. The density of sample was calculated as:
where, W1 and W2 are the weights of the glass samples
in air and in benzene and ρB is the density of buoyant liquid
at 303 K.
||(a) VSP glass samples (system 1) and (b) VPM glass samples
||(a) Longitudinal velocity (UL) and shear velocity for VSP
glass system and (b) Longitudinal velocity (UL) and shear velocity (US)
for VPM glass system
Ultrasonic study: The composition of VSP an VPM glasses in mole% are
shown in Table 1. Also, it clearly predicts the content of
V2O5 increase with decrease of mole% of phosphorous pentoxide
of system 1. Similarly the content of V2O5 increases with
decrease of mole% of MnO2 of system 2. The experimental values of
density, ultrasonic velocity (Longitudinal and Shear) of the different glass
specimen with respect to change in mol% of P2O5 and MnO2
are listed in Table 2a. The calculated longitudinal modulus
(L), shear modulus (G), bulk modulus (K) and youngs modulus (E), are reported
in Table 2b. The perusal Table 3 reports
the value of poissons ratio(σ), acoustic impedance (Z), micro harness
(H), Debyes temperature (θD) and thermal expansion co-efficient
(αp) for the two glass systems (VSP and VPM).
||Values of density (ρ), longitudinal velocity (Ul),
shear velocity (Us) and elastic moduli of VSP and VPM glass systems
It is interesting to note that the density of our glass systems (VSP and VPM
Glass systems) exhibits continuous increases with increase in mol% V2O5
and the higher values of density are reported in VSP glass systems and
hence the magnitudes of density values are in comparison with the order:
VSP glass system>VPM glass system
It is learnt from Table 2 that the values of longitudinal
(U1) and shear velocities (Us) increase linearly with
increase in mol% V2O5 in both VSP and VPM glass systems.
It is seen that the rate of increase of U1 is greater than that of
Us. In the present study of glass systems, the longitudinal ultrasonic
velocity (U1) increases from 4198.29-4699.98 m sec-1 for
VSP glass systems and 4336.04-4931.77 m sec-1 for VPM glass systems.
Similarly, shear velocity (Us) increases from 2464.51-2667.48 m sec-1
for VSP glass and 2464.57-2682.64 m sec-1 for VPM glass systems on
increasing the vanadium content. The increasing trend of both ultrasonic velocities
may be attributed to the increase in rigidity of the glass network.
Addition of V2O5 with P2O5 an MnO2
reply for both glass system increases the elastic moduli such as Longitudinal
Modulus (L), Shear Modulus (G), Bulk Modulus (K) and Youngs Modulus (E)
for both glass (VSP and VPM) systems are clearly shown in Table
2. It also creates (VO4) units and this leads to an increase
in the network dimensionality and connectivity of the network.
Our observed another parameter Poissons ratio increases from 0.237-0.291
for VSP glass systems and from 0.221-0.289 for VPM glass systems.
As seen from Table 3 the values of micro hardness increase
with V2O5 content. The increasing of micro hardness imply
that an increase in the rigidity of the glass system. The monotonous increasing
trend, when V2O5 added with MnO2, V2O5
creates our evaluated values of microhardness are found to be higher in VPM
glass system comparing the VSP glass system, suggesting VPM glass system are
stronger than the VSP glass system.
||Values of Poissons ratio (σ), acousctic impedence
(Z), micro hardness (H), Debye temperature (θD) and thermal
expansion Co-efficient (K-1) of VSP and VPM glass systems
Table 3 describes the variation of Debyes temperature
with V2O5 content. A gradual increase of Debyes
temperature from 145.42-160.06 K for VSP glass systems and from to 143.42 K
for 161.76 VPM glass systems are observed which indicates the increase in the
rigidity of these glass systems. In our present investigation, finds that the
higher values of Debyes temperature reported for VPM glass systems.
X-ray diffraction study: X-Ray diffraction investigation in a Bruker
D8 advanced series (Madison-USA) powder diffractometer using Cu Kα as radiation
source between 20 and 80°. The spectral representations of glass system
VSP and VPM through XRD diffractogram are depicted in Fig. 3a-b.
The absence of crystalline peaks in the XRD patterns of the samples confirms
the amorphous glassy nature.
Spectroscopic study-FTIR interpretation: The FTIR spectra of glasses
were measured at room temperature in the range 4000-400 cm-1 by infrared
spectrophotometer type PerkinElemer Fourier transform using the KBr disc technique.
The glass sample were ground to a fine powder and mixed with KBr. The mixture
was then uniformly pressed with a pressure of 150 kg cm2 to produce
a transparent pellet. The infrared transmission measurement is measured immediately
after preparing the pellets. The Fourier Transformation Infrared absorption
spectra of VSP glass samples (system 1) and VPM glass samples (system 2) are
shown in Fig. 4a-b, respectively.
The FTIR spectral studies confirm the presence of vanadate glass and formation
of P-O-V bond. Table 4 and 5 predicts the
FT-IR spectroscopy peak positions of VSP and VPM glass samples. Table
6 represents the FT-IR spectroscopy band assignments of both VSP and VPM
Scanning electron microscope study (SEM) with EDS: Scanning Electron
Microscope (SEM) has it ability to study the heterogeneity of glass composites
to visualize various minerals components and their relation interms of overall
microfabric and texture. SEM with EDS (Electron Dispersive Study) covers the
observation from the fine structure of specimen surface to the elemental analysis
on a microarea without destroying the specimen.
||(a) XRD diffraction pattern of VSP and (b) VPM glass system
||Peak position of VSP glass sample
||Peak position of VPM glass sample
For material characterization, the VSP and VPM semiconducting glass systems
were taken and dried at hot air oven for about 1 h at 110°C. So, they are
electrically conductive and the samples were powdered well over the surface
of the double-sided adhesive carbon tape. These specimens are coated with the
help of gold-spulter and the surface of the samples were scanned using JFS-1600
JEOL (Akishima Tokyo Japan) autofine coater model of coating time is 120 sec
with 10 mA and deposited with a thin layer of gold on the sample.
||FTIR spectrum for (a) VSP glass samples system 1 and (b) VPM
samples system 2
||(a) SEM micrographs of VSP-glass system and (b) VPM-glass
||Band Assignments of VSP and VPM glass samples
Microstructural study using scanning electron microscope: From the Fig.
5a-b, the SEM micrographs of magnification show the softening
of glass, coalescence between the particles and the morphology of amorphous
nature of VSP and VPM glass systems, respectively. Table 7
reveals the Elemental Analysis of compounds present in the VSP and VPM glass
system, respectively. It is observed that different sized grain particles are
distributed. It consists of densely packed grains free from holes. The particles
are extremely angular and spherical in nature. Some agglomerates structures
were found and also spreads at the surface due to the deposition of amorphous
apatite. This suggests that during formation of glass, the presence of high
percentage of vanadium compounds forms cluster-like composed grain particles
||Elemental analysis of compounds present in the VSP glass system
and elemental analysis of compounds present in the VPM glass system
The pores and cracks at the smooth glassy surface clearly conforms the amorphous
glassy nature of the samples.
Density is an effective tool to explore the degree of structural compactness,
modification of the geometrical configuration of the glass network, change in
co-ordination and the variation of the dimension of the interstitial holes (Rajendran,
2000). The monotonically increase of density with increase of V2O5
concentration can be attributed due the structural changes occurring in the
co-ordination of vanadium glass network.
The V2O5 glasses in which V2O5
as the network former have the network structure mainly consisting of corner-sharing
branched VO4 tetrahedra of the same structural units as found in
phosphor glasses. The network structure was reported to be made up of unaffected
VO5 groups as in vitreous V2O5 and affected
VO5 groups with alkaline earth ions in contrast to the vanadate glasses
formed by conventional network formers in which only unaffected VO5
groups are present (Wright et al., 1985; Sen
and Ghosh, 2001). These glasses are known to contain V4+ and
V5+ hopping of 3 dL unpaired electron from V4+ to V5+
site which introduces a polarization of the vanadium ions around it and forms
a polaron (Chung and Mackenzie, 1980; Ghosh,
Sen and Ghosh (2001) suggested that the addition of
MnO2 and P2O5 to V2O5,
change the present structure to a rigid and compact structure due to change
in the co-ordination number which lead to an increase in ultrasonic velocities.
The observed increase in ultrasonic velocities can also be interpreted as Higazy
and Bridge (1985), where the longitudinal strain in a bond is directly dependant
on the bond stretching force constant. This is inflected in our present system
of glasses, where the longitudinal strain in the main chains (V-O-V linkages)
is affected with the former role of V2O5, due to its increasing
content owing to its high bond strength than that of P2O5
resulting in increase of overall stretching force constant (FB-O). On the other
hand, the shear strain changes with the bond bending force constant (Fb).
Thus, the increase of the shear wave velocity indicates that the decrease in
P2O5 content has a pronounced bending effect on the behavior
of bond bending force constant.
Glass is considered as an elastic substance and it can be characterized through
a modulus of elasticity (Senin et al., 1994).
It is generally known that Oxide glasses doped with the transition metal oxides
such as V2O5, MoO3, WO3, TiO2,
CuO, Fe2O3 etc., are known to exhibit semi conducting
properties and hence these glasses have been extensively studied nowadays. The
concentration of such transition metal oxides such as V2O5
in Vanadate glass plays an active role in semi-conducting glasses (Hirashima
et al., 1985). The elastic properties of these glasses are of considerable
significance, because the studies yield information concerning the forces that
are operative between the atoms comprising as the solid. Hence, the elastic
properties are suitable for describing the glass structure (Saddeek,
2004). This modulus increases as the lengthening of certain applied stress
diminishes. The increase in velocities too is attributed to the increasesing
of rigidity in the glass (Saddeek, 2006).
The increasing trend of elastic moduli in all two glass systems indicates resistance
to deformation and is most probably due to the presence of strong covalent bonds.
Poissons ratio is an effective tool in exploring the degree of cross-link
density of the glass network and its magnitude increases the cross-link density
and it is the ratio of transverse and linear strains for a linear stress. According
to Higazy and Bridge (1985) glass networks having a
connectivity of two (zero cross-link density) have Poissons ratio f =
0.4. Glass networks having connectivity of three (one cross- link density) having
Poissons ratio of = 0.3 while networks having a connectivity of four (two
cross- link density) have Poissons ratio of = 0.15.
Values of Poissons ratio reported in this study from Fig.
6a-b suggest that the network of these glasses has two-dimensional
structure. The increase in Poissons ratio with increasing content of V2O5
is attributed to increase in the average cross-link density of the glass as
proposed by Higazy and Bridge, (1985). Several Vanadium
glasses show semi-conducting behavior and more precisely, vanadium ion containing
glasses are identified as the n-type semiconductors for low value of the V4+/V5+
ratio. The process of hopping of the electrons between V4+ and V5+
ions in the presence of layer concentrations of mobile captions is highly interesting
(Gandhi et al., 2009). The increasing trends
of Poissons ratio in this study are attached to strengthening of network
linkage and attributed to hardening of the network structure.
Micro hardness expresses the stress required to eliminate the free volume (deformation
of the network) of the glass. The present study of increasing value of micro
hardness in all the two glass system studied as shown in Fig.
7a-b indicates an increase in rigidity of the glass. The
softening point is temperature at which viscous flow changes to plastic flow.
It determines the temperature stability of the glass. The higher the value of
softening temperature, the greater is the stability of its elastic properties
(Sidkey et al., 1999).
||(a) Variation of poissons ratio for the VSP glasses
with the composition of P2O5 (mol%) and (b) Variation
of poissons ratio for the VPM glasses with the composition of MnO2
||(a) Variation of micro hardness for the VSP glasses with the
composition of P2O5 (mol%) and (b) Variation of micro
hardness for the VPM glasses with the composition of MnO2 (mol%)
It is also interestingly to note that the continuous increase of Poissons
ratio (σ) as well as micro Hardness (H) in our present study reveals the
absence of Non-Bridging Oxygen (NBO) and this causes the formation of glassy
network. Rajendran (2000) observed that increase in
elastic moduli along with σ and H with addition of glass former confirms
the rigidity and hence there will be formation of stronger structural building
units in this glassy network, when supports our investigation.
Debye temperature (θD) plays an important role in solid materials
in the determination of elastic moduli and atomic vibrations. It represents
the temperature at which all the low frequency lattice vibrational
modes are excited. It is known that θD depends directly on the
mean ultrasonic wave velocity (Varshneya, 1994). Such
an enhancement of Debyes temperature is attributed to the increase in
the number of atoms in the glass and increase in the ultrasonic velocity. One
can notice that the continues increase of Debye temperature from trends of Fig.
8a-b advocates the compactness in the structure leading
to increase in mean sound velocity (El-Mallawany, 2000).
The increase of θD is further corrected to strengthening of
the structural network and hardness. The perusal of Table 3
exhibits the values of acoustic impedance and thermal expansion co-efficient
for the two glass system studied. The increasing trends of these values for
both the glass (VSP and VPM) systems clearly confirms the strengthening of the
Our detailed rigorous study of X-ray diffractgram shows a broad hump which
characteristic of the amorphous structure at around diffraction angle 2θ
= 25-27° to be fully amorphous indicating that these glass samples are composed
of glassy phase (Khattak and Mekki, 2009) with the
observation no peak corresponding to V2O5 indicating that
V2O5 has completely entered the glass matrix and that
the glasses formed were completely amorphous. This indicates the absence of
long range of atomic arrangements and also the periodicity of the three dimensional
network in the quenched materials (Greaves and Sen, 2007).
Our rigorous study from spectroscopic analysis of FTIR interpretation observes
that the infrared absorption band at around the region 438-449 cm-1
is assigned to harmonics of bending vibration of 0 = P-0 linkage (Abid
et al., 2003; Khafagy, 2001). The absorption
band identified at the region 611-646 cm-1 is assigned as deformation
vibration due to V-O-V group, The stretching vibration of Mn-O bond is observed
at the range 618-667.97 cm-1 for the VPM glass samples (Yahia
et al., 2009). These stretching and bending vibrations, are overlapped
with each other. In VPM glass samples, when increasing the composition of V2O5
the vibrational wave numbers are shifted to higher. The FTIR spectra reveal
that vanadium oxide acts as a former of glass network.
||(a) Variation of Debys temperature for the VSP glasses
with the composition of P2O5 (mol%) and (b) Variation
of Debys temperature for the VPM glasses with the composition of MnO2
Some of the infrared vibrational bands of the structural groups of V2O5
lie in the same region as those of P-O-P structural units and hence form
the linkages of the type V-O-P. Vanadium ions take glass network forming position
with VO5 structural units may form linkages of the type V-O-P with
PO4 structural units. The band around 860-878 un-1 is
attributed to the symmetric stretching vibration of V-O bond involved in the
corner sharing of VO5 polyhedral (Yahia et
In VPM glass samples, the content of mole percentage of MnO2 decreases
which results that vibrational wave number shift to lower value. The absorption
region consist of bands due to V = O groups in VO5 trigonal bipyramids
arising out of symmetric stretching at around the region 909.59-984.66 cm-1
(Sharma et al., 2010). In VPM glass samples
the content of P2O5 maintains the constant composition
which shows that the frequency of symmetric stretching mode appeared constant
at the range 1008-1017.08 cm-1 and also it indicates that P-O-P bonds
are strengthened by V2O5 attributes the symmetric stretching
vibration of VO2 groups of VO4 tetrahedral in meta vanadates
forming chains with V-O-V bridges (Socrates, 2004). In
the present study the asymmetric stretching vibrations occurred at the region
1446-1495 cm-1. An absorption band of PO2 asymmetric stretching
vibrations shifts to higher wave number because the phosphorous-oxygen bond
linked to vanadium ions P-O-V (more ionic bonds) (Shaim
et al., 2002). The strong band at about 2350 cm-1 is assigned
to characteristic stretching mode of the P = O bond. Several previous studies
have shown that band corresponding to anti symmetric stretching vibration of
doubly bonded oxygen PO2 could be found in the range 1390-2230 cm-1.
An absorption peak was observed at about 1600 cm-1 is due to H-O-H
bending mode which reflects that samples are quite hygroscopic character of
the powdered glass samples. Generally, there is no significant changes are observed
beyond 1600 cm-1 and also spectra from 1680 cm-1 towards
higher number have the same for all compositions (Khattak
and Mekki, 2009). The bands at 1621-1644 cm-1 are due to O-H
stretching vibration and also, the bands at 2854-3441 cm-1 are assigned
due to O-H bending vibrations of water trapped in the glasses during the experiment.
Due to the hygroscopic nature of P2O5 and it exist in
steady percentage in VPM glass samples gives the band around 1731.51-1742.47cm-1
(Nakamoto, 2008). Hence the OH stretching vibrations
are shifted to the higher wave number. The spectral absorption band of Na2CO3
of VSP glass samples arevery feeble due to conversion from Na2CO3
to Na2O because of its higher glass transition temperature obtained
in furnace. The observed infrared absorption peak at 2840-3460 cm-1
is due to strong hydrogen bonded and super position of symmetric and anti-symmetric
stretching vibration of OH.
||EDS patterns of (a) VSP glass system and (b) VPM glass system
Elemental analysis using electron dispersive X-Ray spectroscopy: EDS
spectral diagram taken for both VSP and VPM glass system as shown in the Fig.
9a-b, respectively. These spectra reveals the presence
of high percentage vanadium along with sodium, phosphate and manganese depending
upon their mole% used in the glass systems. Their weight% and atomic% of above
elemental compounds are shown in Table 7. From the EDS spectral
diagram and from the Table 7, one can observe that vanadium
is more pronounced with in highest value among all the compounds in terms of
weights% as well as atomic%. However, manganese shows its lowest value in terms
of both weight% and atomic% depending upon their molecular weight and mole percentage
taken in the glass systems.
Hence, it is obvious that SEM micrographs and EDS spectral studies are better
tools for exhibiting the presence of sphere shaped large globular like orthorhombic
V2O5 agglomerates were found spreading at the glass surface
due to the deposition of amorphous nature on the average size of 5 μm.
Oxide glasses doped with the transition metal oxides such as V2O5
are known to exhibit semi conducting properties whose electrical conductivity
is due to the electron hopping between V5+ and V4+ ions.
The ultrasonic velocities (UL and US) of VSP and VPM glasses
varying linearly with the addition of glass former (V2O5)
and the magnitude is in the order: VPM>VSP The evaluated acoustical, elastic
and mechanical properties of VPM and VSP glasses throw light on rigidity and
compactness in structural network. The observed increasing trend of micro hardness
and Poissons Ratio for both glass systems (VSP and VPM) indicate VPM glass
system is stronger than VSP systems.
It is very obvious that VPM glass posses higher rigidity and compactness in
structural network over the VSP glass. The functional groups present in our
glass sample have been confirmed by FTIR spectral analysis. The topological
aspects of the glass samples are exhaustively reported from the SEM Micrograph.