Analysis of structural modifications in γ-irradiated PbO–B2O3–SiO2 glasses by FTIR spectroscopy

NIM B Beam Interactions with Materials & Atoms

Nuclear Instruments and Methods in Physics Research B 260 (2007) 613–618 www.elsevier.com/locate/nimb

Analysis of structural modifications in c-irradiated PbO–B2O3–SiO2 glasses by FTIR spectroscopy S. Baccaro a, Monika b, G. Sharma a

a,*

, K.S. Thind b, Devinder Singh b, A. Cecillia

a

ENEA/FIM, Casaccia RC, Via Anguillarese 301, S. Maria di Galeria (Rome) 00060, Italy b Department of Physics, Guru Nanak Dev University, Amritsar 143 005, India Received 11 August 2006; received in revised form 14 April 2007 Available online 24 April 2007

Abstract The effect of c-irradiation on the structure of lead borosilicate glasses of varying composition has been probed by FTIR spectroscopy, before and immediately after c-irradiation. The glasses were irradiated at Calliope 60Co plant (RC ENEA Casaccia, Rome), and the spectra were recorded after absorbed doses of 50 Gy, 500 Gy, and 4 kGy. The structural analysis have been made considering both the effect of composition and of irradiation. The experimental results clearly indicate that after irradiation a significant change in structure of borosilicate glass network is observed. Ó 2007 Elsevier B.V. All rights reserved. PACS: 61.43.Fs; 61.80.Ba; 32.30.Bv Keywords: Borosilicate glasses; c-Irradiation; IR spectra; NBOs

1. Introduction There has been extensive study of the structure of borosilicate glasses by using several techniques as this system has a wide variety of technological applications such as optical lenses, nuclear waste materials, shielding materials and in electronic industry [1–9]. The low melting PbO– B2O3–SiO2 are widely used in semiconductor microelectronics for obtaining passive and insulating layers [10,11]. For this reason it is important to study the influence of various external factors on this glass system [12]. The optimal engineering performance of glasses is dominated by its structure and change in specification within glass network with even small change in composition or processing can have large effects on the properties. The knowledge of the glass structure before and after irradiation is a prerequisite

*

Corresponding author. Tel.: +91 9855015593. E-mail addresses: [email protected] (S. Baccaro), [email protected] (G. Sharma). 0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.04.214

for understanding the structural evolution of glasses under long term irradiation [13]. The investigation of radiation effects leads to a better understanding of the intrinsic structure as well as the alterations, which results from the interaction with radiation. For this reason it is important to study the influence of irradiation on borosilicate glasses [14–20]. A number of studies on borosilicate glasses [21–24] have been reported for irradiation effects on optical, electrical and physical properties of glasses by using density, UV–VIS, XPS, EPS and Raman spectroscopic techniques [25–38]. Much information on this subject can also be provided by vibrational infrared spectroscopy and spectra of glasses can be generally interpreted by considering the vibrations of structural fragments from which the glass network can be built [39–42]. Therefore objective of this work is to produce insight into the structural changes that occur due to c-irradiation in lead borosilicate glasses by using FTIR spectroscopy. Lead content variation from 0.30 mol fraction to 0.75 was chosen since absorption of gamma rays increases with increasing HMO content. The present work will lead to

S. Baccaro et al. / Nucl. Instr. and Meth. in Phys. Res. B 260 (2007) 613–618

fundamental understanding of c-irradiation induced structural modifications in lead borosilicate glasses. 2. Experimental details Commercial grade chemicals of PbO, SiO2 and B2O3 (Aldrich Chemical Company) having 99.99% purity level were used as starting materials. Chemical data for the constituent oxides is shown in ternary phase diagram (Fig. 1). Samples were prepared by using conventional melt-quenching technique. Appropriate amounts of oxides were mixed together using pestle mortar for half an hour. The platinum crucible-containing batch was then placed in an electric furnace capable of reaching a temperature of 1400 °C. It was heated to a temperature of 950 °C for half an hour under normal atmospheric conditions and then dry oxygen was bubbled through it using a quartz tube to ensure homogeneity of the glass melt. The melt was quenched by pouring directly onto a clean metal block. Finally samples were crushed in air using a mortar and pestle. Glasses were irradiated with c-radiation at the Calliope 60 Co plant (RC ENEA Casaccia, Rome) [43] at room temperature. The samples were placed in the dosimetric point corresponding to the dose rate of 574 Gy/h, and each sample was subjected to same sequence of total absorbed doses of 50 Gy, 500 Gy and 4 kGy. Infrared absorption spectra of powdered glass samples were measured in the range 400–4000 cm 1 using KBr technique at room temperature. A recording spectrometer of type Perkin Elmer-1600 was used. Optical measurements were taken before and immediately after irradiation. Infrared spectra were corrected for the dark current noise and background using a two point baseline correction. The spectra were normalized by making absorption of any spectrum varies from zero to one arbitrary units.

0.00

3. Results Figs. 2 and 3 show the baseline corrected normalized infrared spectra of Pb1 glasses before irradiation and after 50 Gy, 500 Gy, 4 kGy of irradiation, respectively. To get quantitative information about the change in structure of Pb1 due to irradiation, the difference between irradiated and unirradiated spectra have been shown in Fig. 4 for 50 Gy, 500 Gy and 4 kGy, respectively. Similarly Figs. 5–13 show spectrum before irradiation, after irradiation and difference spectrum of Pb2, Pb3 and Pb4 glasses, respectively. The active vibrations of the borate and silicate units are in the region of wave number higher than 550 cm 1; thus only the interesting region 600–1800 cm 1 is represented in these figures.

1.4

1.2

1.0

Intensity (a.u)

614

0.8

0.6

0.4

0.2

0.0 600

800

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 2. FTIR spectrum of Pb1 glass (PbO = 0.30, B2O3 = 0.35, SiO2 = 0.35) before irradiation.

2.0

1.00

1.8

Intensity (a.u)

le mo 0.50

on cti fra

0.50

2

mo le

1.4

3

SiO

0.75

B 2O

fra ctio n

1.6

0.25

1.2

After 4 KGy 1.0 0.8

After 500 Gy

0.6

0.75

0.25

0.4 0.2

1.00 0.00

0.00 0.25

0.50

0.75

1.00

PbO mole fraction Fig. 1. Ternary phase diagram of prepared glasses compositions.

0.0 600

After 50 Gy 800

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 3. FTIR spectrum of Pb1 glass after 50 Gy, 500 Gy and 4 kGy of c-irradiation.

S. Baccaro et al. / Nucl. Instr. and Meth. in Phys. Res. B 260 (2007) 613–618

615

0.75

1.6

0.70

After 4 KGy

0.65

1.4

0.60

1.2

0.50

After 500 Gy

0.45 0.40 0.35 0.30

After 50 Gy

Intensity (a.u.)

Intensity (a.u)

0.55

0.25

After 4 KGy 1.0 0.8 0.6 0.4

After 500Gy

0.20

0.2

0.15 0.10

0.0

After 50Gy

0.05 600

800

1000

1200

1400

1600

600

1800

800

Wavenumber (cm-1)

1000

1200

1400

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1800

Wavenumber (cm-1)

Fig. 4. The quantitative spectra of irradiated Pb1 glass with background subtraction of unirradiated Pb1 spectra.

Fig. 6. FTIR spectrum of Pb2 glass after 50 Gy, 500 Gy and 4 kGy of cirradiation.

0.50

1.0

0.45 0.40 0.35

0.6

Intensity (a.u)

Intensity (a.u.)

0.8

0.4

0.2

After 4KGy

0.30 0.25

After 500Gy

0.20 0.15

0.0 0.10

-0.2

After 50Gy

0.05

600

800

1000

1200

1400

1600

1800

0.00 600

Wavenumber (cm-1)

800

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 5. FTIR spectrum of Pb2 glass (PbO = 0.45, B2O3 = 0.30, SiO2 = 0.25) before irradiation.

Fig. 7. The quantitative spectra of irradiated Pb2 glass with background subtraction of unirradiated Pb2 spectra.

For qualitative analysis, the spectra is divided into three regions. The regions are

groups. So both the composition and irradiation effects on vibrational spectra of each glass composition will be considered separately. The relative area of each band is considered proportional to the concentration of the structural group which produces a particular band.

I II III

600–800 cm 1 800–1200 cm 1 1200–1600 cm

1

4. Discussion The spectra in region I have bands at about 680, 700 and 750 cm 1, region II is characterised by a prominent band centred around 1000 cm 1 and region III is dominated by prominent broad peaks around 1300 cm 1. The position of these peaks varies with change in composition and a significant change is observed in spectra before and after successive irradiation (Figs. 2–13). The spectra clearly indicate that c-irradiation induces formation of new structural

4.1. Pb1 glass 4.1.1. Before irradiation The structure of borate glasses as a rule is represented in the form of a three dimensional network whose nodes are occupied by threefold or fourfold coordinated boron atoms. The structural unit in silicate glasses mainly consist

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S. Baccaro et al. / Nucl. Instr. and Meth. in Phys. Res. B 260 (2007) 613–618

1.0

1.0

0.8

Intensity (a.u.)

Intensity (a.u.)

0.8

0.6

After 4KGy

0.6

After 500Gy

0.4

After 50Gy

0.4

0.2 0.2

600

800

1000

1200

1400

1600

0.0 600

1800

800

Wavenumber (cm-1)

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 8. FTIR spectrum of Pb3 glass (PbO = 0.60, B2O3 = 0.20, SiO2 = 0.20) before irradiation.

Fig. 10. The quantitative spectra of irradiated Pb3 glass with background subtraction of unirradiated Pb3 spectra.

1.5 1.4

1.0

1.3 1.2 0.9

Intensity (a.u.)

Intensity (a.u.)

1.1 1.0

After 4KGy

0.9 0.8

0.8

0.7

0.7 0.6

After 500Gy

0.5

0.6

0.4 0.3 600

After 50Gy 800

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 9. FTIR spectrum of Pb3 glass after 50 Gy, 500 Gy and 4 kGy of cirradiation.

of SiO4 tetrahedron and IR absorption spectrum of Si–O stretching region is dominated by a band at 1060 cm 1; whereas the boron structure gives infrared bands around 1000 cm 1 due to stretching vibrations of BO4 tetrahedron [44]. In Fig. 2, the position and intensity of the main broad prominent band from 800 to 1150 cm 1 centred around 1000 cm 1 is assigned to combined stretching vibrations of Si–O–Si and B–O–B network of tetrahedral structural units consisting of borate and silicate groups [41]. A small but significantly clear peak at around 700 cm 1 is attributed to bending vibrations of bridging oxygen between trigonal boron atoms [45]. The broad band observed at 1200–1550 cm 1 centred at 1350 cm 1 is attributed to stretching vibrations of BO3 units with non-bridging oxygens (NBOs) [46–48].

600

800

1000

1200

1400

1600

1800

Wavenumber (cm -1)

Fig. 11. FTIR spectrum of Pb4 glass (PbO = 0.75, B2O3 = 0.15, SiO2 = 0.10) before irradiation.

4.1.2. After irradiation The position of the band around 1000 cm 1 remains same before and after irradiations (Fig. 3). This indicates that even after 4 kGy the glass structure mainly consists of tetrahedral units of borate and silicate groups. This further indicates that four-coordinated atoms lead to an increase in degree of connectivity of the glass forming network and plays a significant role in radiation hardness. In Fig. 4, the difference spectrum before and after irradiation shows a very small but a clear peak around 660 cm 1 and it indicates bending vibrations of BO3 triangles [46–50] formed due to gamma irradiation. The broad hump centred around 1150 cm 1 (Fig. 4) is attributed to Si–O and B–O vibrations of non-bridging oxygens in three coordinated units [51]. The observed band at 1500–1700 cm 1 can be attributed to molecular water vibration [41].

S. Baccaro et al. / Nucl. Instr. and Meth. in Phys. Res. B 260 (2007) 613–618 1.4

1.3

Intensity (a.u.)

1.2

1.1

After 4KGY

1.0

After 500Gy

617

at around 700, 950 and 1300 cm 1 remains the same before and after 50, 500, 4 kGy. The quantitative spectra of irradiated Pb2 glass with background subtraction of the unirradiated glasses is shown in Fig. 7, which clearly indicates a small but sharp peak centered at 670 cm 1 and a broad band can also be observed at 1150 cm 1. This indicates that the number of BO3 units formed after irradiation increase in Pb2 in comparison to Pb1 (Fig. 4). The vibrations of molecular water can also be observed in the region around 1500–1650 cm 1.

0.9

4.3. Pb3 glass 0.8

0.7 600

After 50Gy

800

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 12. FTIR spectrum of Pb4 glass after 50 Gy, 500 Gy and 4 kGy of c-irradiation.

0.60 0.55 0.50

Intensity (a.u.)

0.45

After 4KGY

0.40 0.35

4.3.1. Before irradiation NMR studies of lead borosilicate glasses by Sawvel et al. [51] shows that, with an increase in lead content, the amount of BO3 units and NBOs increases. Fig. 8 shows the spectrum of the Pb3 glass composition with 60 mol% of PbO, and a clear and broad peak can be observed centered at 700 cm 1 attributed to bending of BO3 units, similar to the spectrum of Pb1 shown in Fig. 2 (30 mol% of PbO). The Si–O–Pb vibrations can also be observed at 950 cm 1 in Fig. 8. The vitreous B2O3 peak centered between 1200 and 1300 cm 1 has been attributed to network forming boron species and follows trends observed in lead borate glasses [52]. A shift of the peak from 1350 cm 1 (Fig. 2) to 1250 cm 1 (Fig. 8) has also been observed with an increase in PbO content.

0.30 0.25

After 500Gy

0.20 0.15

After 50Gy

0.10 0.05 0.00 600

800

1000

1200

1400

1600

1800

Wavenumber (cm-1)

Fig. 13. The quantitative spectra of irradiated Pb4 glass with background subtraction of unirradiated Pb4 spectra.

4.3.2. After irradiation The irradiated spectra of Pb3 glass is shown in Fig. 9. The position of bands at 700 cm 1 remains the same as before irradiation even after 4 kGy. A shift of band from 950 to 850 cm 1 is observed in the irradiated spectra. Whereas the band at 1250 cm 1 becomes more broad after irradiation. The difference spectrum of the Pb3 glass with background subtraction of the unirradiated glass is shown in Fig. 10. A clear shoulder at 1260 cm 1 can be observed with a broad band at 1150 cm 1. This indicates formation of super structural units with NBOs after irradiation [46–50].

4.2. Pb2 glass 4.4. Pb4 glass 4.2.1. Before irradiation As lead content is increased, the lead became increasingly incorporated into boron network via B–O–Pb bonding. For the Pb2 glass composition (Fig. 5), the main peak observed at around 950 cm 1 is assigned to vibrations of the Si–O–Pb network [51]. Another prominent band appears at 1328 cm 1 and represents an increase of NBOs with increase in PbO content. A clear peak around 700 cm 1 is also observed for Pb2 in Fig. 5. 4.2.2. After irradiation Fig. 6 shows spectra of Pb2 after 50 Gy, 500 Gy and 4 kGy of irradiation. The position of the three main bands

4.4.1. Before irradiation At low contents of PbO (640 mol%) the lead act as a glass modifier and enters the glass as Pb2+ ions as bonding of lead is strongly ionic, and the cations enter the network in an interstitial manner. Every oxygen atom of PbO added is used to convert two BO3 units to two BO4 units. However, with the increase in mole fraction of lead oxide, the role of cations begin to change. At PbO content greater then 70 mol%, the lead acts as network former and enters the glass as Pb4+ ions [51]. The lead ions are likely to form compact PbO2 pyramidal units taking on a more covalent arrangement. The Pb4 glass composition contains a very high amount of lead oxide (75%), and the spectrum of this

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composition (Fig. 11) shows very sharp peak at 700 cm 1. Further a shift from 950 cm 1 (Fig. 5) to 850 cm 1 (Fig. 11) is also observed with increase in PbO content. Another broad band at 1150 cm 1 (Fig. 11) is attributed to symmetric Si–O vibrations of non-bridging oxygens in three coordinated units. 4.4.2. After irradiation The spectra of irradiated Pb4 glass (Fig. 12) also shows a shoulder near 1250 cm 1 indicating formation of super structural units after irradiation at high content of PbO. In Fig. 13 the quantitative spectra obtained after irradiation shows very clear sharp peaks located at 670 cm 1. A very broad hump can also be observed at 830 and 1120 cm 1. The sharpness of peaks corresponding to BO3 units in this region and almost flat curve around 1000 cm 1 indicates that this glass composition is highly affected by irradiation and dominated by formation of NBO’s due to irradiation. 5. Summary It can be summarized that irradiation leads to structural changes by breaking the bond between BO3 trigonal and SiO4 and BO4 tetragonal structural units. This, leads to increase in non-bridging oxygen ions and increase in formation of super structural units is also observed due to irradiation. The glass with a high amount of PbO (75%) has a more pronounced response to irradiation and diminished intensity of the tetrahedral structural units is observed. Acknowledgements The authors gratefully acknowledge Ms. Elena Mattoni, University of Rome 3, Italy and Angelo Pasquali, ENEA, Casaccia, Roma, Italy for there kind cooperation to perform the measurements. References [1] V. Sudarsan, V.K. Shrikhande, G.P. Kothiyal, S.K. Kulshreshtha, J. Phys. Condens. Matter. 14 (2002) 6553. [2] A.M. Sawvel, S.C. Chinn, W.L. Bourcier, R.S. Maxwell, Chem. Mater. 17 (2005) 1493. [3] T. Takashi, J. Jin, T. Uchino, T. Yoko, J. Am. Ceram. Soc. 83 (2000) 2543. [4] F. Fayon, C. Bessada, D. Massiot, I. Farnan, J.P. Coutures, J. NonCryst. Solids 232–234 (1998) 403. [5] F. Fayon, C. Landron, K. Sakurai, C. Bessada, D. Massiot, J. NonCryst. Solids 243 (1999) 39. [6] K.S. Kim, P.J. Bray, S.J. Merin, J. Chem. Phys. 64 (1976) 4459. [7] D. Stenz, S. Blair, C. Goater, S. Feller, M. Affatigato, J. Non-Cryst. Solids 293–295 (2001) 416. [8] P.J. Bray, M. Leventhal, H.O. Hooper, Phys. Chem. Glasses 4 (2) (1963) 47. [9] A.C. Wright, N.M. Vedischeva, B.A. Shakhmatkin, J. Non-Cryst. Solids 192–193 (1995) 92. [10] P.L. Flowers, J. Electrochem. Soc. 128 (1981) 2179.

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