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Network structure analysis of modifier CdO doped sodium borate glass using FTIR and Raman spectroscopy
Journal of Non-Crystalline Solids xxx (xxxx) xxx–xxx
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Network structure analysis of modifier CdO doped sodium borate glass using FTIR and Raman spectroscopy Mahesh M. Hivrekara, D.B. Sablea, M.B. Solunkeb, K.M. Jadhava,⁎ a b
Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, M.S. 431004, India Department of Physics, Vivekanand Arts, S.D. Commerce and Science College, Aurangabad, M.S. 431001, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Borate glass FTIR Raman spectroscopy
Ternary oxide glass system of chemical composition of 80B2O3–(20-x)Na2O–xCdO (where x = 0, 2, 4, 6, 8, 10, 12, 14 mol%) have been prepared by conventional melting and quenching method. The micro structural and morphological investigation of synthesized glass samples were carried out by using XRD, FE-SEM. The supporting physical and composition dependent properties such as experimental and theoretical density, molar volume, oxygen packing density, ionic concentration, interionic distance and polaron radius were determined. Density of glass samples increases, while molar volume decreases with the increasing cadmium oxide concentration from 0 to 14 mol%. X-ray diffraction profiles and FE-SEM images confirmed amorphous nature of investigated glass samples. Elemental analysis and information about the chemical composition of glass matrices have been ascertained by using EDS spectra. The interpretation of functional groups [BO3] and [BO4] units present in the oxide glass was simulated by using deconvoluted Raman spectra and FTIR spectroscopy. BeO stretching, metal cation active vibrational modes and bending vibrations of BeOeB linkage in borate glass network are cross verified by using FTIR and Raman spectroscopy.
1. Introduction
importance. Since, their use in various technological fields. Heavy metal oxides (PbO and CdO) glasses have also attracted the attention as a result of their high optical nonlinearity and their infrared transmittance [9,10]. CdO can be chosen as network former and network modifier when it is added to network forming oxide glasses, depending upon its concentration. CdO acts in some borosilicate glasses as both network former and network modifier when its content exceeds 50 mol % [9,11]. The addition of alkali oxides to borate glass can improve its physical properties as well as modify the preparation conditions. So that, transition metal oxide (like CdO, ZnO etc.) doped alkali borate glasses are important for photonic and potential battery applications. Also it opens an interesting category of glasses to study the effect of the alkali ion on the glass forming network, particularly the transition metals and rareearth ions [12–15]. CdO is also found to be a promising candidate for optoelectronics, solar cells, photo-diodes and gas sensors etc. Sodium oxide (Na2O), boron trioxide (B2O3) is the major components of many industrial important glasses [16]. The main application of these glasses ranges from cookware to laboratory glassware to optical glass [17]. Because of this reason, many glass researchers have been conducted structural, physical studies to understand how the density, molar mass of each oxide affects the glass network structure.
Borate glasses are having wide variety of applications, it offers varying physical and chemical properties by changing the chemical composition. Boron possesses the ability to change its coordination with oxygen between three or four. Hence it forms variable structural units in the glass network and such behavior is quite different than that of silicon, phosphorous which forms only tetrahedral coordinated units with oxygen. Borate glasses have been extensively studied as a glass forming system [1,2]. Mainly the borate glasses are having so many potential applications like thin amorphous films for battery application, bioactive glasses for tissue engineering, nuclear waste disposal, photonic applications, development of tunable or short pulse lasers, optical fibre amplifiers and fibre lasers etc. [3–7]. Among oxide glasses, borate glass structure having disordered geometry with the formation of tetrahedral coordination of BO4 units. According to, Zacharrisen glass formation theory the oxides of metal cation (e.g. Cd2 +) with valence one or two plays the important role as glass modifier. Some of the bridging oxygen of tetrahedral (BO4) units combines with glass modifier coordinated by six, eight or even more oxygen atom to form glass network with non-bridging oxygen [8]. Recently, oxide glasses containing ZnO and CdO get much
⁎
Corresponding author. E-mail address: [email protected] (K.M. Jadhav).
http://dx.doi.org/10.1016/j.jnoncrysol.2017.08.028 Received 4 July 2017; Received in revised form 29 July 2017; Accepted 19 August 2017 0022-3093/ © 2017 Published by Elsevier B.V.
Please cite this article as: Hivrekar, M.M., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.08.028
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Fig. 1. Flow chart of melting and quenching preparation method of glass.
10 °C/min. During melting process, the glass melt was stirred in order to get homogeneous and bubble free melt. The glass melt was poured and quenched between two well-polished preheated brass plates. The obtained circular disc shaped glass samples were cut and polished carefully with various grit sized micro polish papers for further characterizations.
Subsequent studies include identification of the structural building blocks by using several spectroscopic techniques such as Raman [18], Infrared spectroscopy [19]. This article is focused on the physical, structural study and network analysis of sodium borate glasses and on how the structure of glassy networks is modified by cadmium oxide as dopants belonging to transition metals. The chemical composition-dependent study of present oxide glasses is also summarized in the present article. In the present study analysis of Raman spectra of oxide glass samples was done with the help of Gaussian deconvolution method. This article is very useful for understanding the formation of glassy networks and their modification due to varying CdO concentration.
2.2. Density (ρ), molar volume (Vm) and oxygen packing density (OPD)
2. Experimental
The density of prepared glass samples at room temperature was measured by using Archimedes principle with Xylene as inert immersion liquid (density of Xylene 0.865 g/cm3). Systematic density measurement of three bubble free glass samples were carried out and averaged density is reported in Table 2. The density was calculated with the help of following formula[20,21].
2.1. Synthesis method
ρ=
The oxide glasses with nominal composition of 80B2O3–(20-x) Na2O–xCdO with x = 0, 2, 4, 6, 8, 10, 12, 14 mol% were prepared by conventional melting and quenching techniques. Synthesis method flowchart has been shown in Fig. 1 and the chemical composition and respective codes of oxide glass samples are summarized in Table 1. Raw materials of analar grade (H3BO3, Na2CO3 and CdO with 99.9% purity) are toughly ground for 1 h in an agate mortar and pestle to get homogeneous mixture. The porcelain crucible containing batch was transferred in an electrically heated furnace at a temperature of 450 °C, which helps to remove the moisture, carbonates, decomposition of borate and react with other batch constituents before melting. Then the temperature increased up to 950 ± 50 °C for 2 h with heating rate of
where Wa is the weight of sample in air, Wb is the weight of sample in xylene and ρx is the density of xylene at room temperature. All the weight measurements were carried using a sensitive analytical balance (ViBRA HT) with desired accuracy. Also, the chemical composition dependent theoretical density of the oxide glass samples were calculated for cross checking with the experimental density summarized in the Table 2. The molar volume (Vm) of the glass samples was calculated as the mean molecular mass of the glass composition divided by its density (ρ) [22,23].
Table 1 Chemical composition of 80B2O3–(20-x)Na2O–xCdO (where x = 0, 2, 4, 6, 8, 10, 12, 14 mol%).
where xi is the molar fraction of oxide and Mi is the molecular mass of the oxides present in the glass composition. The sum of these expressed as average molecular mass of the glass sample. In order to measure the tightness of the borate glass network oxygen packing density (OPD) was calculated the using the formula [24]
Glass code
BNC-0 BNC-1 BNC-2 BNC-3 BNC-4 BNC-5 BNC-6 BNC-7
Vm =
Chemical composition (mol%) B2O3
Na2O
CdO
80 80 80 80 80 80 80 80
20 18 16 14 12 10 08 06
00 02 04 06 08 10 12 14
Wa ·ρ (Wa − Wb) x
∑ xi·Mi ρ
OPD =
ρ ×n M
(1)
(2)
(3)
where M is the molecular mass of the glass sample and n is the number of oxygen atoms per formula units. X-ray diffraction pattern was recorded in the range 20–80° with the scanning rate of 5°/min, by using Cu (40 kV, 40 mA) as X-ray source. Powdered glass sample were used to take X-ray diffraction (XRD), scanning electron microscope (FE-SEM), energy dispersive X-ray 2
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Table 2 Physical parameters for different concentration of CdO (0–14 mol%) [average molecular mass M (g/mol), density ρ (g/cm3), molar volume Vm (cm3/mol), oxygen packing density OPD, ionic concentration N (ions/cm3), polaron radius RP (nm), interionic distance Ri (nm)]. CdO mol%
0 2 4 6 8 10 12 14
M (g/mol) ± 0.07
68.09 69.42 70.74 72.07 73.40 74.73 76.06 77.39
ρ (g/cm3) Exp. ± 0.05
Th. ± 0.05
2.19 2.14 2.23 2.39 2.65 2.67 2.73 2.89
2.08 2.13 2.18 2.23 2.29 2.34 2.39 2.45
Vm (cm3/mol) ± 0.42
OPD (g·atm/lit) ± 0.02
N (× 1023 ions/cm3) ± 0.50
Rp (nm) ± 0.03
Ri (nm) ± 0.04
30.97 32.34 31.82 30.12 27.69 27.91 27.77 26.78
83.93 80.40 81.68 86.32 93.89 93.14 93.61 97.07
– 0.74 1.51 2.40 3.48 4.32 5.20 6.30
– 9.58 7.56 6.49 5.73 5.33 5.01 4.70
– 23.76 18.76 16.09 14.21 13.23 12.43 11.66
increasing concentrations of heavier modifier ions get fitted in the interstices which are formed due to the absence lighter sodium oxide, which results increase in the density and decrease in molar volume of the glass network. The small linearity variation in density and molar volume for initial glass samples can be attributed to mixed oxide effect of oxides present in the prepared borate glass. Oxygen packing density (OPD) values of present BNC glass system observes the increasing trend with increasing cadmium oxide concentration as shown in Table 2. This increasing trend of OPD reiterates that it may be due to tightly packed oxygen atoms in the random network of borate glass which supports for the replacement of sodium ions with modifier oxide resulting increase in density of glass samples. Table 2 also reports the values of physical parameters like ionic concentration (N), interionic distance and polaron radius (rP). The interionic distance of the cadmium ions and the polaron radius is found to be decrease with the size of alkali cation while the concentration of the transition metal ions follows an opposite trend.
spectroscopy (EDS) spectra of glass samples. FE-SEM of powdered glass samples was done by a FEI Nova NanoSEM 450 model having ultra-high resolution, low voltage imaging scanning electron microscope with high vacuum environment having the accelerating voltage of 10 kV. To avoid the charge accumulation glass samples were pasted on the carbon film. EDS micro elemental analysis was done by using the Bruker model XFlash 6I30 with excellent energy resolution and element detection range from Beryllium (Be) to Americium (Am). An FTIR spectrum of prepared glass samples was taken by using Bruker instrument at room temperature. For the Raman spectrum, polarized line of 488 nm wavelength Argon ion Laser was used as the excitation source having 150 mW incident power. Similar conditions of back scattering geometry were used for the micro sampling Raman spectrum recording of all the glass samples.
3. Results and discussion 3.1. Physical parameters
3.2. Structural studies
The density of the sodium borate glass linearly increases with increasing concentration of cadmium oxide. It is found to be in the range of 2.19 to 2.89 g/cm3 with the uncertainty of ± 0.05 g/cm3 These values are well matches with the theoretical density values calculated from the glass composition [25]. On the other hand molar volume follows an opposite trend and is found to decrease with the size of the modifier ion i.e. it is maximum for BNC-0 and minimum for BNC-7 as summarized in Table 2. Density and molar volume changing trends as shown in Fig. 2 which can be well explained on the basis of changes occurred in the process of glass network formation. The higher field strength of alkali metal ions (e.g. sodium, lithium etc.) attracts the oxygen ions leading to formation of small sized interstices. The
Studies on x-ray diffraction patterns of Cadmium doped borate glass are shown in Fig. 3. The X-ray diffractograms of other glass samples with increasing concentration of cadmium oxide are having similar shape. Hence, they have not been included showing broad diffuse scattering humps without any sharp crystalline peaks which indicate lack of short range disorder structure. These patterns confirms that glass samples have characteristic of pure amorphous and non-crystalline structure [26]. Field Emission Scanning Electron Microscopy is powerful technique to observe the surface morphology at nanometer level which covers the fine structure surface and elemental analysis of very small area of glass samples without destroying it [27]. Fig. 4(a) and (b) shows FESEM images of BNC-0 and BNC-2 of prepared cadmium doped sodium borate glass samples. FESEM image prepared cadmium doped borate glass shows well-defined distribution of different sized grains with majority of large particles in composite form. Most of the particles having spherical nature with different particle sized grains are observed in each micrograph. Explanation of the surface morphology of glass samples containing agglomeration and aggregation of large particles, with forming the clusters of glass. Energy Dispersive X-ray Spectra (EDS) of prepared glass sample is predicted in the Fig. 5 showing the stoichiometric proportion of elements present in the glass sample. The EDS spectra of cadmium doped sodium borate glass having highest concentration of oxygen atoms and lowest for the cadmium atoms. The inserted table confirmed the total stoichiometric proportion of containing oxides weight and atomic percentage equal to 100% without any external added impurity in the prepared borate glass [28].
Fig. 2. Typical plot of density (ρ), molar volume (Vm) versus different concentration of cadmium oxide (mol%).
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Fig. 3. X-ray diffraction pattern of B2O3-Na2O-CdO amorphous glass.
vibration of the atoms in geometric groups. In the case of glass variables the assignment of vibration peaks of the atoms is very difficult then for IR analysis repetitive occurrence is followed [29]. Raman or IR activity of normal mode of vibrations occurs due to selection rules. Therefore, more information of normal modes of vibration of molecules and crystal lattices can be determined by using IR spectra as compared to Raman spectra. The obtained results of the sample are compared with the large number of compounds containing a common atom group or groups. Some of the absorption peaks are common between them which are assigned the vibration characteristics of those atom groups [30]. Borate glasses are having interesting IR studies with various structural
3.3. FTIR and Raman spectra analysis As glass is well known super cooled liquid with lack of long range order, due to the effect of kinetics process of melt some of the BeO bonds are broken down and condensed glass structure retained. To get this information IR and Raman spectroscopy, two important methods useful for the interpretation of glass structure having diverse active modes of bond deformation, bending, stretching of borate groups. In order to understand the structure and dynamics of amorphous materials like glass and ceramics Infrared and Raman spectroscopy plays vital role. Also it can be useful to assign the absorption peaks with proper
Fig. 4. FE-SEM micrographs of B2O3-Na2O-CdO (a) BNC-0 (b) BNC-2 amorphous glass. system.
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Fig. 5. EDS spectra of 80B2O3-16Na2O-4CdO (BNC-2) amorphous glass.
Fig. 7. Raman spectra of sodium borate glass samples with different concentration of CdO.
main IR regions. FTIR transmittance spectrum of sodium borate glass with different concentration of cadmium oxide reveals the same FTIR spectrum usually obtained from the TM oxide doped alkali borate glass which exhibits the spectral features summarized in Table 3. The RegionIII contains the strong band occurred in the range 1350–1300 cm− 1 found due to the asymmetric stretching vibrations of the BeO bond of trigonal BO3 structural units [33–35]. Region-II includes the weak band in between 1100 and 900 cm− 1 obtained due to the BeO bond stretching vibration of the tetrahedral BO4 structural units [36] and Region-I is observed around 700 cm− 1 because of the bending of BeOeB linkage in the borate networks [37]. The observed peaks are having sharp, medium edges. The characteristic absorption band (806 cm− 1) of the boroxol ring in borate matrix is absent in the present FTIR spectra indicate that the formation of boroxol rings do not occur in the glass system under study [38]. The total alkali oxide content in these glasses is 20 mol%, which converts [BO3] into [BO4] units without formation of non-bridging oxygen ions in the borate matrix. It can be cross verified with the characteristic vibration of 545–550 cm− 1 band observed in initial borate glass samples and get disappeared as CdO concentration increases indicating the formation of [BO4] units that reveals the role of cadmium oxide as network modifier. Similarly, 1020 cm− 1 the stretching vibration of tetrahedral [BO4] units was not observed as CdO concentration increases which means the conversion
Fig. 6. FTIR spectra of sodium borate glass samples with different concentration of CdO.
peculiarities due to boron isotopic anomaly [31,32]. The characteristic vibrations of [BO3] and [BO4] groups e.g. the pentaborate or the ring type borate groups etc. attributed with the help of IR and Raman spectra of borate glasses. The infrared spectra of glass matrix with nominal composition of 80B2O3–(20-x)Na2O–xCdO (where x = 0, 2, 4, 6, 8, 10, 12, 14 mol%) are projected in Fig. 6. Reported literature shows that the FTIR spectra of the borate glasses can be classified into three
Table 3 FTIR band position and respective assignments of cadmium doped sodium borate glass (wavenumber). Reported band position
422, 463, 480 535–550 686–691 765–796 900–1020 1110–1225 1328 1360 1647–1671 2300–3800
Glass sample codes
FT-IR assignment
BNC-0
BNC-1
BNC-2
BNC-3
BNC-4
BNC-5
BNC-6
BNC-7
471 550 691 784 916, 930 1019 1153 1323 1375 1670 –
469 – 691 784 916 1020 1161 1326 1375 – 2359
471 544 686 784 916 1020 1155 1325 1375 – 2361
470 545 669 784 916 1020 1161 1324 1376 – 2359
474 – 669 – 914 – 1216 1363
474 – 669 – 902 – 1217 –
453 – 681 – 932 – 1217 –
485 – 688 – 940 – 1197 –
Vibrations of metal cations in their oxygen sites and respective tetrahedra Vibrations of sodium Na+ through glass network Bending vibrations of BeOeB linkage in borate network Stretching vibrations of BeO bond in [BO4] units from tri-, tetra-, pentaborate Stretching vibrations of tetrahedral [BO4] units
– 2360
Bending modes of OH groups Water, hydroxyl (OH) and (BeOH) groups vibrations
3196
3210
3195
1747 2341 2360 3204
– 2360
3197
1734 2341 2360 3227 3853
3211
3197
5
BeO stretching vibrations of [BO3] units orthoborate groups BeO stretching vibrations of trigonal [BO3]3 − units of pyroborate groups
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Fig. 8. Deconvoluted Raman spectra of sodium borate glass samples with different concentration of CdO.
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4. Conclusions
Table 4 Raman assignments of sodium borate glass with different concentration of cadmium oxide (wavenumber cm− 1). Band position wavenumber (cm− 1)
Raman assignments
135; 171 200–300 548; 551 774–793
Liberational modes of [BO3] and [BO4] units Vibrational modes of Cd-O Deformation mode of BeOeB linkage Breathing vibrations of six membered ring containing [BO3] triangle [BO4] tetrahedra Tetraborate, Pyroborate, orthoborate and diborate groups respectively Stretching vibration of BeO bond borate [BO3] groups BeO stretching of metaborate rings
835–840; 875–1000; 1000–1110 1200; 1266 1300–1600
Borate glass system with nominal composition of 80B2O3–(20-x) Na2O–xCdO (x = 0, 2, 4, 6, 8, 10, 12, 14 mol%) has been successfully synthesized by melt quenching technique. Physical, structural, surface morphology and network structure studies of eight borate glass samples successfully investigated to understand the role of cadmium as a modifier oxide in borate glass network. The XRD, FE-SEM studies confirmed that the prepared glass samples are having purely non crystalline, amorphous nature. EDS confirmed stoichiometric presence of all the elements in prepared borate glass. Due to increasing concentration of CdO the physical parameters like density and OPD increases while molar volume decreases. Borate glass samples increasing CdO attain higher densities and lower molar volume than parent 80B2O3–20Na2O glass composition, supporting decreasing concentration of non-bridging oxygen. From FTIR and Raman spectra, qualitative assignments of different active vibration modes of borate glass network are done. It reveals that increasing content of cadmium oxides, breaking of BeOeB linkage takes place by converting the bridging oxygen (BO) to non-bridging oxygen (NBO). This conversion of [BO3] to [BO4] groups in the prepared glass is in concurrence with density, molar volume and OPD. The cross verification of FTIR information was found to be good agreement with the deconvoluted Raman spectra and decided the role of CdO as glass network modifier.
of borate triangles into [BO4] units without formation of non-bridging oxygen. In the present borate glass system formation of tetrahedral coordination of cadmium [i.e. CdO4] having characteristic absorption band in the region 840 cm− 1 is not present in the IR spectra. The main raw spectrum of Raman spectroscopy as shown in the Fig. 7 is found to be asymmetric in nature. These asymmetries of Raman bands are due to the superimposition of several bands with different line parameters. Interpretation from Raman spectra of oxide glass was quite difficult and uncertain as the Raman bands contain number of peaks with broad noise. In order to overcome these limitations, statistical treatments of deconvolution have been carried out which does not allowed to any bound constraints imposed on the line-parameters and the number of active Raman bands fitted. For that curve fitting of Raman spectra was necessary. It can be possible to separate the overlapped peaks by Gaussian deconvolution method of Raman spectra. Recent IR and Raman spectroscopy analysis techniques includes density functional, wavelet transform and cross-correlation analysis etc. approaches are common tools for analyzing variations in spectral power within the given data series [39–47]. The deconvoluted Raman spectra as shown in Fig. 8 relevant active modes of trigonal [BO3] and tetrahedral [BO4] groups induced due to the polarization of sodium and cadmium ions, by the number of oxygen atoms in a given tetrahedron, and by BeOeB linkage. Goodness of deconvoluted Raman spectra of minimum six and maximum nine peaks fitting can be expressed with parameters r2 and standard error of the fit (r2 ≈ 1 and SE values lies between 1 and 5%). The Raman spectra of 80B2O3–(20-x)Na2O–xCdO with x = 0, 2, 4, 6, 8, 10, 12, 14 mol% glass observed a strong absorption band in the region 200–300 cm− 1 (Table 4) which indicates the vibrational mode of CdeO bond. Two Raman bands with strong and medium intensity observed 420–400; 830–750 cm− 1 (Table 4) which is characteristic band of [BO3] borate group disappears in the IR of BNC-4 to BNC-7. Kamitsos E. et al. assigned the strong band 600–565 cm− 1 and weak band around 1080–1040 cm− 1 to the formation of six membered rings containing one [BO4] tetrahedron, and the shift of this peak towards lower frequency has been assigned to six membered rings with two [BO4] tetrahedra [48–50]. The six membered rings with one [BO4] tetrahedron can be in triborate, tetraborate or pentaborate forms, and rings with two [BO4] tetrahedra can be in diborate, di-triborate or dipentaborate forms. The noticed changes in the kinetics of glass formation converts above mentioned borate groups to [BO4] units decreasing non-bridging oxygen in the expense of bridging oxygen as CdO concentration increases in prepared oxide glass samples [50,51]. The physical parameters and vibrational spectroscopic studies are closely in accordance with each other due to decrease in NBO of random glass network formation supporting the role of cadmium oxide as network modifier.
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Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol
Network structure analysis of modifier CdO doped sodium borate glass using FTIR and Raman spectroscopy Mahesh M. Hivrekara, D.B. Sablea, M.B. Solunkeb, K.M. Jadhava,⁎ a b
Department of Physics, Dr. Babasaheb Ambedkar Marathwada University, Aurangabad, M.S. 431004, India Department of Physics, Vivekanand Arts, S.D. Commerce and Science College, Aurangabad, M.S. 431001, India
A R T I C L E I N F O
A B S T R A C T
Keywords: Borate glass FTIR Raman spectroscopy
Ternary oxide glass system of chemical composition of 80B2O3–(20-x)Na2O–xCdO (where x = 0, 2, 4, 6, 8, 10, 12, 14 mol%) have been prepared by conventional melting and quenching method. The micro structural and morphological investigation of synthesized glass samples were carried out by using XRD, FE-SEM. The supporting physical and composition dependent properties such as experimental and theoretical density, molar volume, oxygen packing density, ionic concentration, interionic distance and polaron radius were determined. Density of glass samples increases, while molar volume decreases with the increasing cadmium oxide concentration from 0 to 14 mol%. X-ray diffraction profiles and FE-SEM images confirmed amorphous nature of investigated glass samples. Elemental analysis and information about the chemical composition of glass matrices have been ascertained by using EDS spectra. The interpretation of functional groups [BO3] and [BO4] units present in the oxide glass was simulated by using deconvoluted Raman spectra and FTIR spectroscopy. BeO stretching, metal cation active vibrational modes and bending vibrations of BeOeB linkage in borate glass network are cross verified by using FTIR and Raman spectroscopy.
1. Introduction
importance. Since, their use in various technological fields. Heavy metal oxides (PbO and CdO) glasses have also attracted the attention as a result of their high optical nonlinearity and their infrared transmittance [9,10]. CdO can be chosen as network former and network modifier when it is added to network forming oxide glasses, depending upon its concentration. CdO acts in some borosilicate glasses as both network former and network modifier when its content exceeds 50 mol % [9,11]. The addition of alkali oxides to borate glass can improve its physical properties as well as modify the preparation conditions. So that, transition metal oxide (like CdO, ZnO etc.) doped alkali borate glasses are important for photonic and potential battery applications. Also it opens an interesting category of glasses to study the effect of the alkali ion on the glass forming network, particularly the transition metals and rareearth ions [12–15]. CdO is also found to be a promising candidate for optoelectronics, solar cells, photo-diodes and gas sensors etc. Sodium oxide (Na2O), boron trioxide (B2O3) is the major components of many industrial important glasses [16]. The main application of these glasses ranges from cookware to laboratory glassware to optical glass [17]. Because of this reason, many glass researchers have been conducted structural, physical studies to understand how the density, molar mass of each oxide affects the glass network structure.
Borate glasses are having wide variety of applications, it offers varying physical and chemical properties by changing the chemical composition. Boron possesses the ability to change its coordination with oxygen between three or four. Hence it forms variable structural units in the glass network and such behavior is quite different than that of silicon, phosphorous which forms only tetrahedral coordinated units with oxygen. Borate glasses have been extensively studied as a glass forming system [1,2]. Mainly the borate glasses are having so many potential applications like thin amorphous films for battery application, bioactive glasses for tissue engineering, nuclear waste disposal, photonic applications, development of tunable or short pulse lasers, optical fibre amplifiers and fibre lasers etc. [3–7]. Among oxide glasses, borate glass structure having disordered geometry with the formation of tetrahedral coordination of BO4 units. According to, Zacharrisen glass formation theory the oxides of metal cation (e.g. Cd2 +) with valence one or two plays the important role as glass modifier. Some of the bridging oxygen of tetrahedral (BO4) units combines with glass modifier coordinated by six, eight or even more oxygen atom to form glass network with non-bridging oxygen [8]. Recently, oxide glasses containing ZnO and CdO get much
⁎
Corresponding author. E-mail address: [email protected] (K.M. Jadhav).
http://dx.doi.org/10.1016/j.jnoncrysol.2017.08.028 Received 4 July 2017; Received in revised form 29 July 2017; Accepted 19 August 2017 0022-3093/ © 2017 Published by Elsevier B.V.
Please cite this article as: Hivrekar, M.M., Journal of Non-Crystalline Solids (2017), http://dx.doi.org/10.1016/j.jnoncrysol.2017.08.028
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Fig. 1. Flow chart of melting and quenching preparation method of glass.
10 °C/min. During melting process, the glass melt was stirred in order to get homogeneous and bubble free melt. The glass melt was poured and quenched between two well-polished preheated brass plates. The obtained circular disc shaped glass samples were cut and polished carefully with various grit sized micro polish papers for further characterizations.
Subsequent studies include identification of the structural building blocks by using several spectroscopic techniques such as Raman [18], Infrared spectroscopy [19]. This article is focused on the physical, structural study and network analysis of sodium borate glasses and on how the structure of glassy networks is modified by cadmium oxide as dopants belonging to transition metals. The chemical composition-dependent study of present oxide glasses is also summarized in the present article. In the present study analysis of Raman spectra of oxide glass samples was done with the help of Gaussian deconvolution method. This article is very useful for understanding the formation of glassy networks and their modification due to varying CdO concentration.
2.2. Density (ρ), molar volume (Vm) and oxygen packing density (OPD)
2. Experimental
The density of prepared glass samples at room temperature was measured by using Archimedes principle with Xylene as inert immersion liquid (density of Xylene 0.865 g/cm3). Systematic density measurement of three bubble free glass samples were carried out and averaged density is reported in Table 2. The density was calculated with the help of following formula[20,21].
2.1. Synthesis method
ρ=
The oxide glasses with nominal composition of 80B2O3–(20-x) Na2O–xCdO with x = 0, 2, 4, 6, 8, 10, 12, 14 mol% were prepared by conventional melting and quenching techniques. Synthesis method flowchart has been shown in Fig. 1 and the chemical composition and respective codes of oxide glass samples are summarized in Table 1. Raw materials of analar grade (H3BO3, Na2CO3 and CdO with 99.9% purity) are toughly ground for 1 h in an agate mortar and pestle to get homogeneous mixture. The porcelain crucible containing batch was transferred in an electrically heated furnace at a temperature of 450 °C, which helps to remove the moisture, carbonates, decomposition of borate and react with other batch constituents before melting. Then the temperature increased up to 950 ± 50 °C for 2 h with heating rate of
where Wa is the weight of sample in air, Wb is the weight of sample in xylene and ρx is the density of xylene at room temperature. All the weight measurements were carried using a sensitive analytical balance (ViBRA HT) with desired accuracy. Also, the chemical composition dependent theoretical density of the oxide glass samples were calculated for cross checking with the experimental density summarized in the Table 2. The molar volume (Vm) of the glass samples was calculated as the mean molecular mass of the glass composition divided by its density (ρ) [22,23].
Table 1 Chemical composition of 80B2O3–(20-x)Na2O–xCdO (where x = 0, 2, 4, 6, 8, 10, 12, 14 mol%).
where xi is the molar fraction of oxide and Mi is the molecular mass of the oxides present in the glass composition. The sum of these expressed as average molecular mass of the glass sample. In order to measure the tightness of the borate glass network oxygen packing density (OPD) was calculated the using the formula [24]
Glass code
BNC-0 BNC-1 BNC-2 BNC-3 BNC-4 BNC-5 BNC-6 BNC-7
Vm =
Chemical composition (mol%) B2O3
Na2O
CdO
80 80 80 80 80 80 80 80
20 18 16 14 12 10 08 06
00 02 04 06 08 10 12 14
Wa ·ρ (Wa − Wb) x
∑ xi·Mi ρ
OPD =
ρ ×n M
(1)
(2)
(3)
where M is the molecular mass of the glass sample and n is the number of oxygen atoms per formula units. X-ray diffraction pattern was recorded in the range 20–80° with the scanning rate of 5°/min, by using Cu (40 kV, 40 mA) as X-ray source. Powdered glass sample were used to take X-ray diffraction (XRD), scanning electron microscope (FE-SEM), energy dispersive X-ray 2
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Table 2 Physical parameters for different concentration of CdO (0–14 mol%) [average molecular mass M (g/mol), density ρ (g/cm3), molar volume Vm (cm3/mol), oxygen packing density OPD, ionic concentration N (ions/cm3), polaron radius RP (nm), interionic distance Ri (nm)]. CdO mol%
0 2 4 6 8 10 12 14
M (g/mol) ± 0.07
68.09 69.42 70.74 72.07 73.40 74.73 76.06 77.39
ρ (g/cm3) Exp. ± 0.05
Th. ± 0.05
2.19 2.14 2.23 2.39 2.65 2.67 2.73 2.89
2.08 2.13 2.18 2.23 2.29 2.34 2.39 2.45
Vm (cm3/mol) ± 0.42
OPD (g·atm/lit) ± 0.02
N (× 1023 ions/cm3) ± 0.50
Rp (nm) ± 0.03
Ri (nm) ± 0.04
30.97 32.34 31.82 30.12 27.69 27.91 27.77 26.78
83.93 80.40 81.68 86.32 93.89 93.14 93.61 97.07
– 0.74 1.51 2.40 3.48 4.32 5.20 6.30
– 9.58 7.56 6.49 5.73 5.33 5.01 4.70
– 23.76 18.76 16.09 14.21 13.23 12.43 11.66
increasing concentrations of heavier modifier ions get fitted in the interstices which are formed due to the absence lighter sodium oxide, which results increase in the density and decrease in molar volume of the glass network. The small linearity variation in density and molar volume for initial glass samples can be attributed to mixed oxide effect of oxides present in the prepared borate glass. Oxygen packing density (OPD) values of present BNC glass system observes the increasing trend with increasing cadmium oxide concentration as shown in Table 2. This increasing trend of OPD reiterates that it may be due to tightly packed oxygen atoms in the random network of borate glass which supports for the replacement of sodium ions with modifier oxide resulting increase in density of glass samples. Table 2 also reports the values of physical parameters like ionic concentration (N), interionic distance and polaron radius (rP). The interionic distance of the cadmium ions and the polaron radius is found to be decrease with the size of alkali cation while the concentration of the transition metal ions follows an opposite trend.
spectroscopy (EDS) spectra of glass samples. FE-SEM of powdered glass samples was done by a FEI Nova NanoSEM 450 model having ultra-high resolution, low voltage imaging scanning electron microscope with high vacuum environment having the accelerating voltage of 10 kV. To avoid the charge accumulation glass samples were pasted on the carbon film. EDS micro elemental analysis was done by using the Bruker model XFlash 6I30 with excellent energy resolution and element detection range from Beryllium (Be) to Americium (Am). An FTIR spectrum of prepared glass samples was taken by using Bruker instrument at room temperature. For the Raman spectrum, polarized line of 488 nm wavelength Argon ion Laser was used as the excitation source having 150 mW incident power. Similar conditions of back scattering geometry were used for the micro sampling Raman spectrum recording of all the glass samples.
3. Results and discussion 3.1. Physical parameters
3.2. Structural studies
The density of the sodium borate glass linearly increases with increasing concentration of cadmium oxide. It is found to be in the range of 2.19 to 2.89 g/cm3 with the uncertainty of ± 0.05 g/cm3 These values are well matches with the theoretical density values calculated from the glass composition [25]. On the other hand molar volume follows an opposite trend and is found to decrease with the size of the modifier ion i.e. it is maximum for BNC-0 and minimum for BNC-7 as summarized in Table 2. Density and molar volume changing trends as shown in Fig. 2 which can be well explained on the basis of changes occurred in the process of glass network formation. The higher field strength of alkali metal ions (e.g. sodium, lithium etc.) attracts the oxygen ions leading to formation of small sized interstices. The
Studies on x-ray diffraction patterns of Cadmium doped borate glass are shown in Fig. 3. The X-ray diffractograms of other glass samples with increasing concentration of cadmium oxide are having similar shape. Hence, they have not been included showing broad diffuse scattering humps without any sharp crystalline peaks which indicate lack of short range disorder structure. These patterns confirms that glass samples have characteristic of pure amorphous and non-crystalline structure [26]. Field Emission Scanning Electron Microscopy is powerful technique to observe the surface morphology at nanometer level which covers the fine structure surface and elemental analysis of very small area of glass samples without destroying it [27]. Fig. 4(a) and (b) shows FESEM images of BNC-0 and BNC-2 of prepared cadmium doped sodium borate glass samples. FESEM image prepared cadmium doped borate glass shows well-defined distribution of different sized grains with majority of large particles in composite form. Most of the particles having spherical nature with different particle sized grains are observed in each micrograph. Explanation of the surface morphology of glass samples containing agglomeration and aggregation of large particles, with forming the clusters of glass. Energy Dispersive X-ray Spectra (EDS) of prepared glass sample is predicted in the Fig. 5 showing the stoichiometric proportion of elements present in the glass sample. The EDS spectra of cadmium doped sodium borate glass having highest concentration of oxygen atoms and lowest for the cadmium atoms. The inserted table confirmed the total stoichiometric proportion of containing oxides weight and atomic percentage equal to 100% without any external added impurity in the prepared borate glass [28].
Fig. 2. Typical plot of density (ρ), molar volume (Vm) versus different concentration of cadmium oxide (mol%).
3
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Fig. 3. X-ray diffraction pattern of B2O3-Na2O-CdO amorphous glass.
vibration of the atoms in geometric groups. In the case of glass variables the assignment of vibration peaks of the atoms is very difficult then for IR analysis repetitive occurrence is followed [29]. Raman or IR activity of normal mode of vibrations occurs due to selection rules. Therefore, more information of normal modes of vibration of molecules and crystal lattices can be determined by using IR spectra as compared to Raman spectra. The obtained results of the sample are compared with the large number of compounds containing a common atom group or groups. Some of the absorption peaks are common between them which are assigned the vibration characteristics of those atom groups [30]. Borate glasses are having interesting IR studies with various structural
3.3. FTIR and Raman spectra analysis As glass is well known super cooled liquid with lack of long range order, due to the effect of kinetics process of melt some of the BeO bonds are broken down and condensed glass structure retained. To get this information IR and Raman spectroscopy, two important methods useful for the interpretation of glass structure having diverse active modes of bond deformation, bending, stretching of borate groups. In order to understand the structure and dynamics of amorphous materials like glass and ceramics Infrared and Raman spectroscopy plays vital role. Also it can be useful to assign the absorption peaks with proper
Fig. 4. FE-SEM micrographs of B2O3-Na2O-CdO (a) BNC-0 (b) BNC-2 amorphous glass. system.
4
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Fig. 5. EDS spectra of 80B2O3-16Na2O-4CdO (BNC-2) amorphous glass.
Fig. 7. Raman spectra of sodium borate glass samples with different concentration of CdO.
main IR regions. FTIR transmittance spectrum of sodium borate glass with different concentration of cadmium oxide reveals the same FTIR spectrum usually obtained from the TM oxide doped alkali borate glass which exhibits the spectral features summarized in Table 3. The RegionIII contains the strong band occurred in the range 1350–1300 cm− 1 found due to the asymmetric stretching vibrations of the BeO bond of trigonal BO3 structural units [33–35]. Region-II includes the weak band in between 1100 and 900 cm− 1 obtained due to the BeO bond stretching vibration of the tetrahedral BO4 structural units [36] and Region-I is observed around 700 cm− 1 because of the bending of BeOeB linkage in the borate networks [37]. The observed peaks are having sharp, medium edges. The characteristic absorption band (806 cm− 1) of the boroxol ring in borate matrix is absent in the present FTIR spectra indicate that the formation of boroxol rings do not occur in the glass system under study [38]. The total alkali oxide content in these glasses is 20 mol%, which converts [BO3] into [BO4] units without formation of non-bridging oxygen ions in the borate matrix. It can be cross verified with the characteristic vibration of 545–550 cm− 1 band observed in initial borate glass samples and get disappeared as CdO concentration increases indicating the formation of [BO4] units that reveals the role of cadmium oxide as network modifier. Similarly, 1020 cm− 1 the stretching vibration of tetrahedral [BO4] units was not observed as CdO concentration increases which means the conversion
Fig. 6. FTIR spectra of sodium borate glass samples with different concentration of CdO.
peculiarities due to boron isotopic anomaly [31,32]. The characteristic vibrations of [BO3] and [BO4] groups e.g. the pentaborate or the ring type borate groups etc. attributed with the help of IR and Raman spectra of borate glasses. The infrared spectra of glass matrix with nominal composition of 80B2O3–(20-x)Na2O–xCdO (where x = 0, 2, 4, 6, 8, 10, 12, 14 mol%) are projected in Fig. 6. Reported literature shows that the FTIR spectra of the borate glasses can be classified into three
Table 3 FTIR band position and respective assignments of cadmium doped sodium borate glass (wavenumber). Reported band position
422, 463, 480 535–550 686–691 765–796 900–1020 1110–1225 1328 1360 1647–1671 2300–3800
Glass sample codes
FT-IR assignment
BNC-0
BNC-1
BNC-2
BNC-3
BNC-4
BNC-5
BNC-6
BNC-7
471 550 691 784 916, 930 1019 1153 1323 1375 1670 –
469 – 691 784 916 1020 1161 1326 1375 – 2359
471 544 686 784 916 1020 1155 1325 1375 – 2361
470 545 669 784 916 1020 1161 1324 1376 – 2359
474 – 669 – 914 – 1216 1363
474 – 669 – 902 – 1217 –
453 – 681 – 932 – 1217 –
485 – 688 – 940 – 1197 –
Vibrations of metal cations in their oxygen sites and respective tetrahedra Vibrations of sodium Na+ through glass network Bending vibrations of BeOeB linkage in borate network Stretching vibrations of BeO bond in [BO4] units from tri-, tetra-, pentaborate Stretching vibrations of tetrahedral [BO4] units
– 2360
Bending modes of OH groups Water, hydroxyl (OH) and (BeOH) groups vibrations
3196
3210
3195
1747 2341 2360 3204
– 2360
3197
1734 2341 2360 3227 3853
3211
3197
5
BeO stretching vibrations of [BO3] units orthoborate groups BeO stretching vibrations of trigonal [BO3]3 − units of pyroborate groups
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Fig. 8. Deconvoluted Raman spectra of sodium borate glass samples with different concentration of CdO.
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4. Conclusions
Table 4 Raman assignments of sodium borate glass with different concentration of cadmium oxide (wavenumber cm− 1). Band position wavenumber (cm− 1)
Raman assignments
135; 171 200–300 548; 551 774–793
Liberational modes of [BO3] and [BO4] units Vibrational modes of Cd-O Deformation mode of BeOeB linkage Breathing vibrations of six membered ring containing [BO3] triangle [BO4] tetrahedra Tetraborate, Pyroborate, orthoborate and diborate groups respectively Stretching vibration of BeO bond borate [BO3] groups BeO stretching of metaborate rings
835–840; 875–1000; 1000–1110 1200; 1266 1300–1600
Borate glass system with nominal composition of 80B2O3–(20-x) Na2O–xCdO (x = 0, 2, 4, 6, 8, 10, 12, 14 mol%) has been successfully synthesized by melt quenching technique. Physical, structural, surface morphology and network structure studies of eight borate glass samples successfully investigated to understand the role of cadmium as a modifier oxide in borate glass network. The XRD, FE-SEM studies confirmed that the prepared glass samples are having purely non crystalline, amorphous nature. EDS confirmed stoichiometric presence of all the elements in prepared borate glass. Due to increasing concentration of CdO the physical parameters like density and OPD increases while molar volume decreases. Borate glass samples increasing CdO attain higher densities and lower molar volume than parent 80B2O3–20Na2O glass composition, supporting decreasing concentration of non-bridging oxygen. From FTIR and Raman spectra, qualitative assignments of different active vibration modes of borate glass network are done. It reveals that increasing content of cadmium oxides, breaking of BeOeB linkage takes place by converting the bridging oxygen (BO) to non-bridging oxygen (NBO). This conversion of [BO3] to [BO4] groups in the prepared glass is in concurrence with density, molar volume and OPD. The cross verification of FTIR information was found to be good agreement with the deconvoluted Raman spectra and decided the role of CdO as glass network modifier.
of borate triangles into [BO4] units without formation of non-bridging oxygen. In the present borate glass system formation of tetrahedral coordination of cadmium [i.e. CdO4] having characteristic absorption band in the region 840 cm− 1 is not present in the IR spectra. The main raw spectrum of Raman spectroscopy as shown in the Fig. 7 is found to be asymmetric in nature. These asymmetries of Raman bands are due to the superimposition of several bands with different line parameters. Interpretation from Raman spectra of oxide glass was quite difficult and uncertain as the Raman bands contain number of peaks with broad noise. In order to overcome these limitations, statistical treatments of deconvolution have been carried out which does not allowed to any bound constraints imposed on the line-parameters and the number of active Raman bands fitted. For that curve fitting of Raman spectra was necessary. It can be possible to separate the overlapped peaks by Gaussian deconvolution method of Raman spectra. Recent IR and Raman spectroscopy analysis techniques includes density functional, wavelet transform and cross-correlation analysis etc. approaches are common tools for analyzing variations in spectral power within the given data series [39–47]. The deconvoluted Raman spectra as shown in Fig. 8 relevant active modes of trigonal [BO3] and tetrahedral [BO4] groups induced due to the polarization of sodium and cadmium ions, by the number of oxygen atoms in a given tetrahedron, and by BeOeB linkage. Goodness of deconvoluted Raman spectra of minimum six and maximum nine peaks fitting can be expressed with parameters r2 and standard error of the fit (r2 ≈ 1 and SE values lies between 1 and 5%). The Raman spectra of 80B2O3–(20-x)Na2O–xCdO with x = 0, 2, 4, 6, 8, 10, 12, 14 mol% glass observed a strong absorption band in the region 200–300 cm− 1 (Table 4) which indicates the vibrational mode of CdeO bond. Two Raman bands with strong and medium intensity observed 420–400; 830–750 cm− 1 (Table 4) which is characteristic band of [BO3] borate group disappears in the IR of BNC-4 to BNC-7. Kamitsos E. et al. assigned the strong band 600–565 cm− 1 and weak band around 1080–1040 cm− 1 to the formation of six membered rings containing one [BO4] tetrahedron, and the shift of this peak towards lower frequency has been assigned to six membered rings with two [BO4] tetrahedra [48–50]. The six membered rings with one [BO4] tetrahedron can be in triborate, tetraborate or pentaborate forms, and rings with two [BO4] tetrahedra can be in diborate, di-triborate or dipentaborate forms. The noticed changes in the kinetics of glass formation converts above mentioned borate groups to [BO4] units decreasing non-bridging oxygen in the expense of bridging oxygen as CdO concentration increases in prepared oxide glass samples [50,51]. The physical parameters and vibrational spectroscopic studies are closely in accordance with each other due to decrease in NBO of random glass network formation supporting the role of cadmium oxide as network modifier.
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