Structural Study through Magnetic and Spectroscopic Properties on ...

Vol.2, No.2-3, 83-91(2011)
BO 3 units
BO 4 units
B-O-B & TiO 4
Transmittance, %
Ti-O-Ti
PbO 4 units
F 7
F 6
F 5
F 4
F 3
F 2
F 1
F 0
2000
1800
1600
1400
1200
1000
800
600
400
Wavenumber (cm -1 )
Fig. 4: IR spectra of PbO-TiO 2 -B 2 O 3 :Fe 2 O 3 glasses.
The OA spectra of prepared glasses recorded in the wavelength region 350-1100 nm are shown in Fig. 5. The
absorption edge observed at 401 nm for the glass F 0 is observed to shift to 378 nm when we move from F 0 to F 5 .
With further increase in the concentration of Fe 2 O 3 , the edge is observed to shift gradually towards higher
wavelength. The spectra of the glasses F 1 , F 2 , F 3 , F 4 <strong>and</strong> F 5 have exhibited absorption b<strong>and</strong>s at 540, 580 <strong>and</strong> 787 nm
due to Fe 3+ ion transitions <strong>and</strong> a b<strong>and</strong> at 955 nm due to Fe 2+ ions is observed in the spectra of F 6 <strong>and</strong> F 7 . With
increase in the concentration of Fe 2 O 3 beyond 0.5 mol %, the b<strong>and</strong>s due to Fe 3+ ions have been observed to fade
away slowly where as the intensity of the b<strong>and</strong> due to Fe 2+ ions is observed to increase gradually. Urbach plot is
drawn between (αћω) 1/2 <strong>and</strong> ћω <strong>and</strong> this plot is represented in Fig (6). In Fig. 6, it is clear that some part of each
curve of every sample is linear. The values of optical b<strong>and</strong> gap (E o ) obtained from the extrapolation of the linear
portions of these plots are presented in Table 4. The value of E o is found to increase with the increase in
concentration of Fe 2 O 3 from 0.1 to 0.5 mol % from a value 2.32 eV to 2.65 eV later on this value is decreased to 2.2
eV on further increasing the dopent to 0.7 mol %.
The ESR spectra of prepared glasses recorded at room temperature are shown in Fig. 7. The intensity of the ESR
signal is observed to increase gradually with increase in the concentration of Fe 2 O 3 in the glass matrix up to 0.5 mol
%. This intense line centered at about g = 2. However, the intensity of this signal is decreased with the increase of
the concentration of Fe 2 O 3 beyond 0.5 mol %. In the spectra of all the prepared samples a weak signal at g=4.3 also
be detected.
<strong>Magnetic</strong> susceptibility of the prepared glasses measured at room temperature is observed to increase with
increase in Fe 2 O 3 content in the glass composition (Table 5) up to 0.5 mol %, beyond that the susceptibility is found
to decrease. From the values of magnetic susceptibilities, the effective magnetic moments (µ eff ) are evaluated <strong>and</strong>
presented in Table 5. The value of µ eff is found to increase gradually from a value of 5.2 (for glass F 1 ) to a value of
5.8 µ B (for glass F 5 ) with increase of Fe 2 O 3 up to 0.5 mol %. Later on with the increase of Fe 2 O 3 in the glass matrix
the magnetic moment is decreased.
B 2 O 3 is a well known glass former. Both lead oxide <strong>and</strong> titanium dioxide are modifiers. The introduction of PbO <strong>and</strong>
TiO 2 into B 2 O 3 glass network is to convert the sp 2 planar BO 3 into more stable sp 3 tetrahedral BO 4 units in addition
to non-bridging oxygens (NBO’s). The existence of such BO 4 units in the present glass system is evident from IR
spectral studies.
When PbO is added into B 2 O 3 glass network it enters into the glass network by breaking up the B-O-B bonds <strong>and</strong>
introduces coordinate defects known as dangling bonds along with non-bridging oxygen ions. PbO may also
participate in the glass network with PbO 4 structural units when lead ion is linked to four oxygens in a covalency
bond configuration. Addition of TiO 2 in small quantities will enhance the glass forming ability <strong>and</strong> chemical
durability of the glasses. Ti ion enters the glass network in Ti 4+ state <strong>and</strong> participate in the glass network forming
with TiO 4 , TiO 6 <strong>and</strong> some times with TiO 5 structural units. Ti 4+ ions are expected to improve the non-linear optical
properties of lead borate glasses. The structure of the PbO-TiO 2 -B 2 O 3 : Fe 2 O 3 glass is represented in Fig. 8.
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T.V. Nagalakshmi et al.