J Mater Sci: Mater Electron (2015) 26:3722–3729 DOI 10.1007/s10854-015-2891-9
Investigation on structural and optical properties of SLS–ZnO glasses prepared using a conventional melt quenching technique M. H. M. Zaid • K. A. Matori • H. J. Quah • W. F. Lim • H. A. A. Sidek • M. K. Halimah W. M. M. Yunus • Z. A. Wahab
•
Received: 22 December 2014 / Accepted: 27 February 2015 / Published online: 6 March 2015 Ó Springer Science+Business Media New York 2015
Abstract Zinc oxide soda lime silica, (ZnO)x(SLS)1-x glasses were synthesized using conventional solid-state melt quenching in water technique. The addition of zinc oxide (ZnO) into soda lime silica (SLS) glass had caused the reduction of glass melting temperature, transition temperature and crystallization temperature. The composition of the glass was studies using EDXRF spectrometry. Glassy nature of the glass samples was confirmed using X-ray diffraction measurement. Various vibrational modes
M. H. M. Zaid K. A. Matori H. A. A. Sidek M. K. Halimah W. M. M. Yunus Z. A. Wahab Department of Physics, Faculty of Science, Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia e-mail:
[email protected] H. A. A. Sidek e-mail:
[email protected] M. K. Halimah e-mail:
[email protected] W. M. M. Yunus e-mail:
[email protected] Z. A. Wahab e-mail:
[email protected] K. A. Matori (&) W. F. Lim Materials Synthesis and Characterization Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia e-mail:
[email protected] W. F. Lim e-mail:
[email protected];
[email protected] H. J. Quah Materials Processing and Technology Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia (UPM), 43400 Serdang, Selangor, Malaysia e-mail:
[email protected];
[email protected]
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were determined from the region of 400–4000 cm-1 for the investigated (ZnO)x(SLS)1-x glasses using fourier transform infrared (FTIR) spectroscopy. It was revealed that the incorporation of ZnO into the SLS glass network had caused the rearrangement of the glass bonding and splitting of Si–O–Si bonding that would enhance the formation of non-bridging oxygens (NBOs). The formation of more NBOs had resulted in an increment in the density and molar volume, whereby the optical band gap of the (ZnO)x(SLS)1-x glasses was decreased from 3.66 to 3.42 eV.
1 Introduction In recent years, soda lime silica (SLS) glasses from bottle banks that consist mainly of silicon dioxide (SiO2), sodium oxide (Na2O) and calcium oxide (CaO) has attracted much attention. This is owing to the low temperature viscous flow sintering of SLS glass, which has promoted it as a good candidate for total or partial replacement of the natural fluxes [1]. Besides, SLS glasses have been known their good glass forming nature when compared with other conventional glasses. SLS glasses possess fine optical and mechanical properties, such as good chemical stability, high ultraviolet (UV) transparency, low thermal expansion coefficient, leading to strong thermal resistance, low nonlinear refractive index, high surface damage threshold, large tensile fracture strength, and good durability [2, 3]. To-date, SLS glasses have been doped with transition metal and/or rare earth oxides, and being used as radiationsensitive dosimeter [4], or for the fabrication of low cost integrated optical amplifiers [5], and other commercial tableware and sheet glasses [6]. Despite the presence of binary compounds, such as SiO2, TeO2, and B2O3, which are
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considered as good glass formers, it is essential to incorporate foreign compounds in order to improve suitability of the SLS glasses to various applications. Therefore, technical glasses containing conditional network formers (Al2O3, ZnO), network modifiers (Li2O, Na2O), and refining agents (As2O3) can be used for fining the melt and to minimize formation of bubbles in the final glass product. Particular interest has been devoted to ZnO for its properties, which include wide band gap (*3.37 eV) [7] and high dielectric constant values [8] that have enabled the employment of ZnO in the fabrication of electronic and optical devices, such as laser diodes and light emitting diodes [9, 10]. Besides, it has been also widely used as a window material in solar cells, optical waveguides, light modulators and optical sensors. Radiation resistance of ZnO has also made it a suitable candidate for space applications [11]. Apart from these, ZnO has been promising candidate regarding its effect upon addition on borate and tellurite system [12, 13]. However, the reports in the literatures regarding the addition of ZnO into SLS glass system have not been really understood, leading to no definitive answers to the fundamental topics. Thus far, literatures showed that the addition of ZnO into SLS glasses increased mechanical properties, improved chemical durability, and lowered the glass transition temperature [14, 15]. In addition, due to the small field strength and high polarizibility of the Zn2? ions, ZnO can hardly be used as a network former, except in the presence of conventional glass former like SiO2, which eventually form a glass network of ZnO (n = 3, 6) pyramids [16]. Xiang et al. [17] assumed that in sodium zinc silicate glasses, Zn can exist either in a tetrahedral (network former) or octahedral (network modifier) coordination, depending on the concentration of sodium and the sixfold coordination being preferred at low alkali concentration while Lusvardi et al. [18] found that Zn2? could act as a weak tetrahedral network former independently on the Na-content of the glass. In the light of above, since there is a lack of systematic study on SLS glassed doped with ZnO previously, it is therefore of interest to investigate in present work the effects of ZnO doping onto the structural and optical properties of (ZnO)x(SLS)1-x glasses with the help of X-ray diffraction (XRD), differential thermal analysis (DTA), fourier transform infrared spectroscopy (FTIR), ultraviolet–visible (UV– vis) spectroscopy, density and molar volume measurements.
2 Experimental details 2.1 Preparation of glasses A series of glass samples of formula (ZnO)x(SLS)1-x with 0 B x B 50 wt% were prepared using conventional melt
3723
quenching in water technique. The required amount of chemicals, ZnO and waste SLS glass powder were mixed together via grinding to obtain fine powders (size \ 45 lm). The obtained mixture was melted in an alumina crucible at a temperature of 1300 °C for 2 h until a homogenous bubble free liquid was formed. The molten mixture was then poured into the water and formed transparent glass frit. Each glass frit produced was optically clear and showed no inclusion in it. The glass frit was then ground in a vibratory mill jar to produce fine glass powder (\45 lm). After the addition of 1.75 wt% Polyvinyl Alcohol (PVA) binder, the powder was pressed at a pressure of 5 tons for 10 min to form discs with a diameter of 10 mm and thickness of 2 mm for subsequent analysis. Using nondestructive EDXRF measurement, the composition of the glass samples (G1–G6) employed in the present study are tabulated in Table 1. 2.2 X-ray diffraction (XRD) The amorphous/crystalline nature of the glass samples is confirmed by XRD characterization using Philips X-ray diffractometer with Cu-Ka radiation in the 2h range from 10° to 90° using 0.02° steps. 2.3 Differential thermal analysis (DTA) The thermal behavior of the glass was determined using DTA technique. The DTA scans were carried out on glass powders with particle size ranging from 45 to 100 lm, using a Diamond Pyris TG/DTA (Perkin Elmer) with Al2O3 powder as reference material in a dynamic pure nitrogen atmosphere at a flow rate of 50 cm3 min-1 at the temperature range between 400 and 900 °C at 10 °C min-1.
2.4 Fourier transforms infrared spectroscopy (FTIR) Infrared spectroscopy absorption spectral measurements were carried out on powdered glass samples at room temperature in the region 400–4000 cm-1 using Perkin Elmer Spectrum 100 spectrometer with Universal attenuated total reflectance (ATR) accessory. FTIR spectroscopy work with controlled an interactive pressure so that the sample will make a good contact with the diamond, resulting in high quality and reproducible spectra. A quantitative analysis for the infrared spectrum has been carried out by a careful deconvolution of the absorption profiles utilizing a computer based program which considers hidden peaks at wave numbers different from local maximum in the data stream.
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3724 Table 1 Chemical composition of glass samples
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Glass sample
SiO2
CaO
Na2O
Al2O3
K2O
MgO
Fe2O3
B2O3
BaO
G1
69.5
11.3
12.5
2.8
1.5
2.0
0.2
0.1
0.1
0
G2
62.6
10.2
11.3
2.4
1.3
1.9
0.1
0.1
0.1
10.0
G3
55.6
9.1
10.0
2.2
1.2
1.7
0.1
0.1
0.1
19.9
G4
48.7
7.9
8.8
1.9
1.1
1.5
0.1
0.1
0.1
29.8
G5
41.7
6.8
7.5
1.6
0.9
1.3
0.1
0.1
0.1
39.9
G6
34.9
5.7
6.3
1.3
0.7
1.0
0.1
0.1
0.1
49.8
ZnO
2.5 Density and molar volume measurement
2 aðxÞ ¼ B hv Eopt =hv
The density of glass samples at room temperature is measured by the standard principle of Archimedes using a sensitive micro-balance with acetone liquid as the immersion fluid. The sample was first weighed in air, Wair, and then in an immersion acetone, Wac, with the following density: qac = 0.789 g cm-3. The weighing process was performed with an electronic balance. The density of the sample was then calculated using the following relationship [Eq. (1)]:
where Eopt is the optical energy gap, hv is the photon energy and B is a constant called band tailing parameter. The relation can be written as ðahvÞ1=2 ¼ B hv Eopt ð5Þ
q ¼ Wair qac =ðWair Wac Þ
ð2Þ
where MT is the total molecular weight of the multi-component glass system given as [Eq. (3)]: MT ¼ xi Zi
Using this relation, Eopt values are determined by extrapolation of linear region of the plots of (ahv)1/2 against hv to (ahv)1/2 = 0
ð1Þ
where the estimated error was ±0.001 g cm-3. The molar volume (Vm) was measured in cm3 mol-1 for liquids and solids and can be expressed as [Eq. (2)]: Vm ¼ RMT =q
ð4Þ
ð3Þ
where xi is the mole fraction of the ith oxides, and Zi is the molecular weight of the ith oxides.
3 Results and discussion 3.1 Energy dispersive X-ray fluorescence (EDXRF) EDXRF spectrometry is a non-destructive analytical technique successfully used in the characterisation of glass samples. Chemical compositions present in the glass samples were analyzed EDXRF as shown in Table 1. It was deduced that compounds like SiO2, CaO, Na2O, Al2O3, K2O, MgO, Fe2O3, B2O3, BaO and ZnO were detected in the samples. The increase of ZnO content to the SLS glass has resulted in a percentage reduction of other elements in the glass samples.
2.6 Ultraviolet–visible (UV–vis) 3.2 X-ray diffraction (XRD) The optical absorption spectra of the glass samples are recorded at room temperature using UV–vis spectrophotometer (Lambda 35, Perkin Elmer) in the wavelength region from 300 to 800 nm. One of the major problems is that samples often precipitate due to the particle size not being small enough, making the absorption spectrum difficult to analyze. In order to avoid these consequences, it is preferable to use a Reflectance Spectroscopy Accessory (RSA), which reliably obtains the optical band gap of powder samples. Sabri et al. [19] used diffuse reflectance spectroscopy for powdered ZnO for optical properties measurement for varistor application. It was assume that for this study, the fundamental absorption edge of the glasses is due to the indirect transition. The relation between a(x) and the photon energy of incident radiation hx is given by the relation
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XRD patterns (Fig. 1) of the glass samples showed no continuous or discrete sharp peaks but exhibited broad peak, which reflected amorphous nature of the glass samples. All of the prepared glass samples confirmed the glassy nature. It was observed that the broad peak was shifted from lower diffraction angle (*23°) for sample G1 to higher angle (*33°) for sample G6 and became less broadening with the increase of ZnO content (Table 1; Fig. 1). The observation might be attributed to the substitution of Na? or Ca2? ions in the SLS glasses with Zn2? ions. Hence, the shift of the broad peaks approaching to the diffraction angles associated with ZnO was observed and could be related with a smaller ionic radius of the Zn2? ions (*72 pm) than that of Na? ions (*102 pm) and Ca2? ions (*100).
J Mater Sci: Mater Electron (2015) 26:3722–3729
3725
Fig. 1 X-ray diffraction pattern of (ZnO)x(SLS)1-x glasses
23˚
33˚
Intensity (a.u.)
G6 G5 G4 G3 G2 G1 10
20
30
40
50
60
70
80
90
2θ
3.3 Differential thermal analysis (DTA) Effects of the ZnO doping on DTA of all of the glass series at a heating rate of 10 °C min-1 are shown in Fig. 2a. A decrease of the glass transition temperature (Tg) and crystallization temperature (Tp) can be attributed to the increase of ZnO content in the SLS glasses (Fig. 2b). This is due to the ability of higher amount of ZnO in reducing the melt viscosity that would lead to a decrease of the Tg and Tp of the glass network by approximately 50–60 °C. 3.4 Fourier transforms infrared (FTIR) spectroscopy FTIR spectroscopy has been used to detect the presence of different functional groups in the SLS glasses doped with different ZnO contents using wavenumbers ranging from 400 to 1400 cm-1, as show in Fig. 3. By further interpreting the first region, the absorption band was generally characterized by three distinguished sub-regions. The first sub-region lying around 400–505 and 550–600 cm-1 was associated with Si–O–Si and O–Si–O bending modes in the glass network while the second sub-region at 700–820 cm-1 was due to Si–O–Si symmetric stretching of bridging oxygen between tetrahedral [20–22]. After the addition of ZnO to the SLS glass system, the transmittance band at 750–770 cm-1 was shifted to a higher transmittance band, indicating the formation of Si– O–Zn bonds in the glass network and this suggested the formation of ZnO4 units at the expense of ZnO3 units. The third sub-region extending from 820 to 1400 cm-1 was due to Si–O–Si antisymmetric stretching of bridging oxygen within the tetrahedra [23]. It was summarized from the findings that the FTIR spectrum existing in the first region from 400 to 1400 cm-1 consisted of the absorption due to the presence of vibrations attributed to the main silicate network group with different bonding arrangements [24–26].
In this work, findings from the FTIR studies on (ZnO)x(SLS)1-x glasses have shown that the structure of such glasses is generally independent on the content of silica network and the constitution has retained the tetravalent valence for the main Si4? ion [27]. The fundamental building block in SLS glass is the SiO4 tetrahedral unit with all the oxygens shared between two tetrahedra. After the addition of ZnO into the SLS glass network, there may be a small change at the band shift. It was anticipated that the observation might be due to presence of Zn2? ions that act as network modifiers in the SLS glass system and the possibility of the Zn2? ions to break the bridging oxygen bonds to form non-bridging oxygens (NBOs). 3.5 Density and molar volume The density of studied glasses increases with the addition of ZnO in SLS glass network which is shown in Fig. 4. The density of glasses was measured to understand the molecular packing inside the glasses. Density of the (ZnO)x (SLS)1-x glass samples is increased with the increment of ZnO concentration due to presence of the heavier zinc atomic mass (65.390) compared to the other element in the glass samples, such as atomic mass of Si (28.086), Ca (40.078) and Na (22.989). An increase in the density of (ZnO)x(SLS)1-x glass sample has also resulted in the changes of the crosslink density due to the formation of new linkages in the (ZnO)x(SLS)1-x glass structure [28]. The Zn2? ion tends to occupy interstitial sites within the highly open glass network that caused splitting of Si–O–Si bond, whereby BOs is converted to NBOs. The formation of NBOs will decrease the connectivity of the glass sample that contributes to the weakening of the glass structures [29]. This weakening process was observed as the density of glass sample was increased with the addition of ZnO content.
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3726
(a) 710 520 721
Exo.
Fig. 2 a DTA curves of (ZnO)x(SLS)1-x glasses. b Glass transition and crystallization temperature versus wt% of ZnO contents in (ZnO)x(SLS)1-x glass system
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535
732
550
Endo.
G6 G5
740
560
G4
745
568
G3
750
G2
573 400
500
G1 600
700
800
900
Temperature (ºC)
(b)
800
Tg
750
Tc
Temperature (ºC)
700 650 600 550 500 450 400
0
10
20
30
40
50
Si-O-Si Sym
G6 G5
% Transmittance (a.u.)
O-Si-O
Si-O-Si
Fig. 3 FTIR spectra of (ZnO)x(SLS)1-x glasses (in range 400–1400 cm-1)
ZnO4
ZnO (wt.%)
400
G4 G3 G2
Si-O-Si Asym
G1
500
600
700
800
900
Wavelength
The obtained molar volume results of the (ZnO)x (SLS)1-x glasses, which is having a similar trend to the density (ZnO)x(SLS)1-x glasses (Fig. 4), further supported the occurrence of glass weakening process. Hence, (ZnO)x(SLS)1-x glasses would lose its glass structure when the content of ZnO in the glasses is being increased due to
123
1000
1100
1200
1300
1400
(cm-1)
the increase in bond length or inter atomic spacing among the atoms of glass network [30]. Besides the formation of NBOs in the glass structure due to the presence of Zn2? ions, the reduction in the composition of alkali or alkaline oxide would also increased the number of NBOs in the glass structure [31]. A decrease in the concentration of
J Mater Sci: Mater Electron (2015) 26:3722–3729
3727 25
2.95 2.9
Density
Density (g/cm3)
2.85
24.8
Molar volume 24.6
2.8 2.75
24.4
2.7 24.2
2.65 2.6
24
2.55
23.8
2.5 2.45
Molar volume
Fig. 4 The density and molar volume versus wt% of ZnO contents in (ZnO)x(SLS)1-x glasses
0
10
20
30
40
50
60
23.6
ZnO (wt.%)
modifier oxide would increase the concentration of tetrahedral that has resulted in the formation of a relatively compact structure. However, in this study, the addition of ZnO content to the SLS glass structure has resulted in the weakened of glass network structure. The increased in molar volume has indicated that the NBOs bond produced by the ZnO was greater than those produced by alkaline oxides. Hence, the formation of these NBOs bond would increase the atomic distance of the composition in the glass samples and reduced the rigidity of the glasses. 3.6 Optical band gap Figure 5 shows optical absorption spectrum of (ZnO)x (SLS)1-x glass system. It was clear that no sharp absorption edge which corresponds to the characteristic of glassy state was observed [32, 33]. It was also observed from Table 2 that the fundamental absorption edge has shifted to a longer wavelength when the content of ZnO was
increased. This might be due to the less rigidity of the glass system as the ZnO content was increased. Using Eq. (5), Eopt values were determined by extrapolation of linear region of the plots of (ahv)1/2 against hv to (ahv)1/2 = 0 as shown in Fig. 6. The obtained values of optical energy gap were decreased from 3.66 to 3.42 eV as the content of ZnO was increased (Table 2). The obtained optical energy gaps of the investigated samples were close to reported values by Chimalawong et al. [34]. The addition of ZnO to SLS glass network has caused the breakdown of a continuous SiO4 network, whereby a significant shift of the absorption edge to longer wavelengths was observed. The shifting of absorption edge were more likely related to structural rearrangements of the glass and relative concentrations of various fundamental units. Rosmawati et al. [35] has suggested that the movement of absorption band to a lower energy was due to NBOs, whereby the electrons were loosely bonded to NBOs than BOs. The results obtained in the Fig. 6 have indicated a decreased in optical energy gap as the ZnO content was
1.2
Fig. 5 Wavelength versus absorbance for (ZnO)x(SLS)1-x glasses
G1
Absorbance (a.u.)
1
G2 G3
0.8
G4
0.6
G5 G6
0.4 0.2 0 300
400
500
600
700
800
Wavelength (nm)
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3728 Table 2 Glass Composition, glass transition, crystallization temperature, density, molar volume and optical band gap of the glass samples, respectively
J Mater Sci: Mater Electron (2015) 26:3722–3729
Sample
Empirical formula
Tg (°C)
Tp (°C)
q
Vm
Eopt
G1
(ZnO)0(SLS)1.0
573
750
2.520
23.926
3.66
G2
(ZnO)0.1(SLS)0.9
568
745
2.573
24.058
3.59
G3
(ZnO)0.2(SLS)0.8
560
740
2.630
24.180
3.55
G4
(ZnO)0.3(SLS)0.7
550
732
2.689
24.315
3.51
G5
(ZnO)0.4(SLS)0.6
535
721
2.749
24.472
3.45
G6
(ZnO)0.5(SLS)0.5
520
710
2.842
24.727
3.42
4.2
4.4
Fig. 6 (ahv)1/2 as a function of energy for (hv) (ZnO)x(SLS)1-x glasses
2.5
G1
(αhv)1/2 (cm-1 eV)1/2
2
G2 G3
1.5
G4 G5
1
G6
0.5
0
3
3.2
3.4
3.6
3.8
4
Energy (hv) (eV)
increased, whereby breaking of SLS glass structure happened due to the increment of NBOs ion content.
support provided by Universiti Putra Malaysia (UPM) under UPM Post-Doctoral Fellowship Scheme.
4 Conclusion
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