ISRN SpectroscopyVolume 2012 (2012), Article ID 896492, 5 pagesdoi:10.5402/2012/896492

Research Article

Effect of Stepwise Replacement of Non-Oxide to Oxide Group on Structural Properties of ·LiF· Glasses

Susheel Arora,¹ Virender Kundu,² D. R. Goyal,¹ and A. S. Maan¹

¹Department of Physics, Maharshi Dayanand University, Rohtak 124 001, India²Department of Electronic Science, Kurukshetra University, Kurukshetra 136 119, India

Received 2 August 2012; Accepted 28 August 2012

Academic Editors: V. Di Noto, A. A. Ensafi, and S. Yannopoulos

Copyright © 2012 Susheel Arora et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

Bismuth fluoroborate glasses with compositions xBi₂O₃·(40 − x)LiF·60 B₂O₃ (x = 0, 5, 10, 15, and 20) are synthesized by melt-quench method. XRD pattern is obtained for all the samples to confirm their amorphous nature. FTIR spectroscopy is carried out for the reported samples. It reflects the effect of replacement of a non-oxide group (LiF) with an oxide group (Bi₂O₃) in the glass network, due to the presence of the various absorption bands and their shifting with such replacement, assigning a role of network modifier to Bi₂O₃. Density and molar volume show an increase in their values with increase in Bi₂O₃ concentration. Theoretical optical basicity is calculated for the reported samples, which shows a decreasing trend with the increasing concentration of Bi₂O₃.

1. Introduction

B₂O₃ is one of the best glass formers due to the sheet-like structure of boron-oxygen triangles in borate glasses, with their ability to connect themselves to form a network [1, 2]. A random arrangement of various atomic and molecular species is easily formed in borate glasses which is the basic requirement for glass formation. A number of modifications in the properties of the borate glasses, with the addition of alkali halides, have been reported so far [3–9]. The inclusion of LiF in the borate glass network brings out some structural changes [3], which in turn become responsible for the change in various properties. Some new units like BO₂F, BO₂F₂, BOF₃, and BO₃F are formed by the replacement of few oxygen atoms by fluorine ions [4–6]. Also, there may be an increase in the number of polyhedral groups of boron and oxygen, which in turn increases the number of nonbridging oxygen atoms [7–9].

Bi₂O₃ possesses high third-order nonlinear optical susceptibility caused by high density and refractive index [10, 11]. This property makes it to have numerous nonlinearity applications such as optical switching [12, 13], supercontinuum generation [14], and wavelength conversion [15]. Luminescent materials have always been studied by researchers for their wide range of applications. Noto reported the luminescence spectroscopy of some systems containing rare earth ions [16, 17]. Also, bismuth ion acts as an efficient luminescent activator with applications in lasers as a sensitizer for some rare earth ions [18, 19]. The purpose of this paper is to report the change in structural and physical properties of glasses with the stepwise replacement of LiF by Bi₂O₃. The addition of provides an opportunity for the new molecular units to be formed with more numbers of NBOs.

2. Experimental Details

Bi₂O₃ containing fluoroborate glasses with compositions (x = 0, 5, 10, 15,  and  20) were synthesized through melt-quench method using , LiF and , reagent grade powders. A uniform mixture of the various powdered samples was prepared and heated at 1273 K for 30 minutes. The bubble free melt so formed was pressed between two carbon plates at room temperature. The glassy samples were thus obtained in the form of thin pallets.

The samples were tested for their amorphous nature on Rigaku X-ray diffractometer using Cu-Kα radiations. The samples grinded to powdered form were placed in the diffractometer and rotated at 1°/min.

FTIR spectroscopy was carried out at room temperature in the range from 652 to 4000 cm⁻¹. The samples were exposed to the IR radiations in Perkin-Elmer FTIR spectrophotometer. A plot between % transmission and wave number is obtained to examine various bonds formation in view of absorption bands obtained in the plot.

Densities () of the samples were calculated at room temperature using Archimedes’ principle with xylene was taken as an inert immersion liquid.

3. Results and Discussion

3.1. XRD Analysis

The X-ray diffraction pattern for glasses with is plotted in Figure 1. The patterns contain broad bands but do not contain any peak, which confirms the amorphous nature of the samples.

Figure 1: XRD plots for samples with in the compositions ..

3.2. FTIR Analysis

Figure 2 corresponds to the Fourier transform infrared spectra of the compositions , with . The spectra were recorded in the range, 652–4000 cm⁻¹. However, absorption bands obtained in the range of 1700–4000 cm⁻¹ correspond to those due to water groups, the said range is not shown in the figure.

Figure 2: FTIR plots for samples with in the compositions .

In the composition with , there appears an absorption band around 685 cm⁻¹. This absorption is attributed to the bending of B–O–B linkage in the borate network [20]. However for the compositions with , in general, this absorption becomes very weak which reveals that the structural changes are taking place due to the addition of . For all the samples, there appears an absorption band with small but increasing intensity, around 779 cm⁻¹. This absorption is due to the formation of B–F bonds [21]. This indicates that due to addition of , structure of the glass is greatly affected as fluorine gets encouraged to take interstitial positions in the glass network. In the composition with , the absorption band around 910 cm⁻¹ is attributed to the B–O bond stretching in units of diborate groups [22]. In the compositions except , there appears another band originating at 901 cm⁻¹. Intensity of this band increases with increase in concentration. It may be due to the Bi–O and Bi–O–Bi bonds in octahedra [20, 21, 23–25].

For the samples with , inclusion of in the host composition facilitates the presence of more oxygen atoms in the glass network. The availability of these oxygen atoms encourages the formation of more pentaborate and diborate species [26, 27] in the glass network. Presence of these species is attested by the increasing intensity band in at 1100 cm⁻¹, which is almost absent in .

In the literature [22, 26, 28], the absorption range 1160–1600 cm⁻¹ is assigned to the B–O bond stretching vibrations in BO₃ units. Here one can observe two sub-bands in all the compositions. For , the sub-bands are centered at 1220 cm⁻¹ and 1365 cm⁻¹. The former band corresponds to the stretching vibrations of B–O bonds in units from meta and ortho-borate groups [21, 22, 25–28] and the later is due to the B–O asymmetric stretching vibrations in BO₃ and units [22, 25, 26]. For the compositions other than , these sub-bands appear at 1210 cm⁻¹ and 1370 cm⁻¹ respectively, with an enhanced intensity. The enhancement in the intensity of the band centered at 1210 cm⁻¹ may be due to the formation of more units in meta and ortho borate groups with the addition of oxygen containing molecule in the glass network. The increasing intensity of the band centered at 1370 cm⁻¹ is due to the presence of units in the samples other than that with [23]. In addition to these two high-intensity bands, there exists a shoulder absorption at 1295 cm⁻¹ for the samples with concentration. This shoulder absorption is assigned to the units [29] and also may be due to Bi–O–Bi vibrations of octahedral units [23]. Furthermore the absorption band centered at 1440 cm⁻¹ and 1530 cm⁻¹ in all the samples except , is due to BO⁻ stretching vibrations of units from varied types of borate groups [30].

All these results are summarized in Table 1.

Table 1: FTIR absorption assignments of the samples with x = 0, 5, 10, 15, and 20 in the compositions .

Wavenumber (cm⁻¹)
Assignment

685
Bending of B–O–B linkage in borate network

779
B–F bonds

901
Bi–O and Bi–O–Bi bands in BiO₆ octahedra

910
B–O bond stretching in BO₄ units

1100
Pentaborate and diborate species

1210, 1220
Stretching vibrations of B–O bonds in BO₃ units from meta and orthoborate groups

1295
BO₂F units and Bi–O–Bi vibrations of BiO₆ octahedral units

1365
B–O asymmetric stretching vibrations in BO₃ and units

1370
BiO units

1440, 1530
B-O⁻ stretching vibrations of BO₃ units from varied types of borate groups

3.3. Density and Molar Volume

Using Archimedes principle, density (D) of all the samples was calculated, and its values are ploted against   mol% in Figure 3. It is observed that density of the samples increases with increasing concentration of . This shows that the atomic and molecular species get more closely packed with the addition of . The increase of the density of the glasses with the addition of Bi₂O₃ is probably attributable to a change in cross-link density and coordination numbers of Bi³⁺ ions [30]. It is supported by another fact that has larger molar mass as compared to LiF, so the replacement of LiF by makes the density to increase.

Figure 3: Density and Molar Volume of the samples with in the compositions .

The molar volume () of each glass sample was calculated using the formula [31] where is the molar fraction and is the molecular weight of the th component. It also increases with the increase in content.

3.4. Theoretical Optical Basicity

Optical basicity is an important parameter related to the optical properties of the glasses. Electronic polarizability and optical basicity have an intrinsic relationship. Optical basicity is expressed in terms of the electron density carried by anions. Theoretical optical basicity for the present series of samples is calculated using following formula [32]: Here is the ratio of number of cations “” to total number of oxide ions, is basicity modulating factor, is the oxidation number of cations “” and is the oxidation number of corresponding anions. The basicity moderating parameter “” can be calculated from the following equation: where “” is Pauling’s, electronegativity of the cation. Values of are plotted in Figure 4. It is observed that theoretical optical basicity decreases with increase in content.

Figure 4: Theoretical Optical Basicity of the samples with in the compositions .

4. Conclusions

Study of the series of amorphous materials with compositions   x = 0, 5, 10, 15  and  20 reflects following conclusions(1)XRD analysis, suggests that the samples are amorphous in nature as the XRD spectra of all the samples contain no sharp peak.(2)In FTIR analysis it can be concluded that plays an important role in modifying the glass network. The presence of the absorption bands at 901, 1295, and 1370 cm⁻¹ attests these modifications which are due to content and are absent in the sample with . Further, an important conclusion is that with the addition of in place of some concentration of LiF, there is an almost elimination of an absorption band (685 cm⁻¹) and shifting of some absorption band centers (1210 to 1220 cm⁻¹ and 1365 to 1370 cm⁻¹) from to , which approves the role of Bi₂O₃ as a network modifier in the present glass system.(3)Density and molar volume increase with increase in content due to replacement of a larger molar mass group () with a smaller molar mass group (LiF).(4)Theoretical optical basicity decreases with increase in content on the cost of LiF content.

Acknowledgment

The financial support provided to one of the authors (S. Arora) by CSIR, New Delhi (India), is gratefully acknowledged.

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