Effect of Nd2O3 addition on structure and ...

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Effect of Nd2O3 addition on structure and characterization of lead bismuth borate glass q

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I. Kashif a,⇑, A. Abd El-Maboud a, A. Ratep b

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Physics Department, Faculty of Science, Al-Azhar University, Nasr City, 11884 Cairo, Egypt Physics Department, Faculty of Girls, Ain Shams University, Heliopolis, Cairo, Egypt

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Article history: Received 23 July 2013 Accepted 22 November 2013 Available online xxxx Keywords: Nd oxide addition on oxide glass X-ray diffraction (XRD) Differential thermal analysis (DTA) Infrared spectrophotometer (FTIR) Optical absorption Density

a b s t r a c t The effect of different contents of Nd2O3 on the thermal transition temperature, density and structure of 25 Bi2O3 – 25 PbO – 50 B2O3 has been investigated using X-ray diffraction (XRD), differential thermal analysis (DTA), infrared spectrophotometer (FTIR) and optical absorption. The amorphous phase has been identified based on X-ray diffraction analysis. The neodymium oxide plays the role as a glass-modifier and influences on BO3 M BO4 conversion. The observed increase in Tg with Nd2O3 reflects an increase in bond strength. The decrease of the density and the increase of the molar volume with the addition of Nd2O3 contents attributed to an increase in the number of Non-bridging oxygen (NBOS). The optical absorption results are indicating the higher covalency of the Nd–O bond for glass containing 2 mol% of Nd2O3. In addition, a lowest covalency is observed in glass with 1 mol% Nd2O3. In addition, it is considered necessary in the construction of compact and efficient laser source. Ó 2013 The Authors. Published by Elsevier B.V. All rights reserved.

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Introduction

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The development in information technology depends on the materials that are effective for information transmission, power transmission and nonlinear applications. Glasses based on heavy metals such as Bismuth and Lead has high refractive index, due to their higher hyperactive polarizable nature. Since these glasses exhibit nonlinear phenomenon, they are valuable in optical fibers and in optical switches [1–3]. Borate glass has many properties such as, high transparency, low melting temperature, high thermal stability, different coordination numbers, and good solubility of rare earth ions, although it is very suitable for optical material. The addition of heavy metal oxide to borate glasses decreases the phonon energy. Thus, leads to an increase in its quantum efficiency of luminescence from the exited state of rare earth ions. Further, the addition of rare earth oxide to alkali borate glasses is interesting for studying effects of its ions on the glass forming network [4–6]. Mohan [7] investigated the physical and spectroscopic properties for sodium lead borate glasses doped with varying amounts of Nd3+. Density measurement indicates that the density decreases with the increase in concentration of Nd3+ ions up to 1.75 mol%.

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This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. ⇑ Corresponding author. Tel.: +20 02 24558035. E-mail addresses: [email protected], [email protected] (I. Kashif).

The decrease in density could be due to the formation of non-bridging oxygen (NBO’s) atoms. From the spectroscopic measurements obtained the indirect and direct mobility gap have a maximum for 2 mol% and a minimum for 1 mol% of Nd2O3. The direct mobility gap shows the same behavior of density, and the indirect mobility gap does not follow a uniform variation. Borate glasses have two groups of different coordination; first one is trigonal BO3 coordination and the second is the tetrahedral BO4 coordination. These two fundamental coordinations can be combined to form different groups like boroxol rings, orthoborate, pentaborate, tetraborate, metaborate and diborate groups, etc. The BO4 units give rise to tetrahedral network features in the glass structure [8], where BO4 units are always negatively charged ([BO4/2]), whereas BO3 units may be present as („ [BO3/2]0), charged units [BO2/2O](„ B2), [BO1/2O2]2(„ B1) or even [BO3]3(„ B0) [9].The fraction of these BO4 and structural units depends on the nature and concentration of the added modifiers [10–15]. Thermal and optical properties of glasses Bi2O3B2O3 system were studied. The optical transparent glasses Bi2O3B2O3 containing rare earth ions or nano-regions of ferroelectric crystals are of more interest, because such materials have potential for laser host, tunable waveguide and tunable fiber grating [16–19]. Heavy metal oxide glasses (Bi2O3 and PbO) have many applications in the field of glass ceramics, layers for optical and electronic devices, thermal and mechanical sensors, reflecting windows, etc. [20]. Neodymium oxide is used to dope glass, including sunglasses, make solid-state lasers, and to color glasses and enamels. Also, used in ceramic capacitors, color TV tubes, high temperature

2211-3797/$ - see front matter Ó 2013 The Authors. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.rinp.2013.11.002

Please cite this article in press as: Kashif I et al. Effect of Nd2O3 addition on structure and characterization of lead bismuth borate glass2O3 addition on

Q1 structure and characterization of lead bismuth borate glass –>. Results Phys (2013), http://dx.doi.org/10.1016/j.rinp.2013.11.002

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glazes, coloring glass, carbon-arc-light electrodes, and vacuum deposition. In the present work, the effect of Nd2O3 on the structure, glass forming ability and density of glass samples were studied using different techniques such as XRD, DTA, IR and optical absorption measurements.

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Experimental

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Reagent grades H3 BO3, Bi2O3, PbO and Nd2 O3 were used as starting materials for preparing glasses having the composition 25 Bi2O3 – 25 PbO – 50 B2O3 – x Nd2O3 mol%, (0 6 x 6 2) where x varies from 0 to 2 in steps of 0.5. Initially the samples were maintained at about 550 °C for 2 h for de-carbonization of carbonate. Then the temperature was raised up to 800 °C and maintained for two hours. Subsequently, the temperature was further increased up to 1000 °C and maintained for one and half an hour depending upon the composition. Then the molten liquid was poured between two stainless steel mold plates kept at room temperature for the formation of glassy composition of required shape. The glassy nature of the samples were confirmed by XRD studied using Philips Analytical X-ray diffraction system, type PW3710 based with Cu tube anode of wave length Ka1 = 1.54060 Å and Ka2 = 1.54439 Å. The generator tension was 40 kV and the generator current was 30 mA. The start angle (2h) was 10° and the end angle was 70°, the step size (2h) was 0.02 and the time per step was 1.0 s. In the present work, analysis by infrared spectrometer was carried out using FTIR 6300; Tosco, Japan absorption spectra in the region 400–4000 cm1 were recorded for all the samples using KBr pellets technique. The glassy nature of the prepared glasses was confirmed by the differential thermal analysis (DTA) in the temperature range from 30 to 1200 °C with the heating rate of 30 °C/min (in N2 gas atmosphere) of using Al2O3 powder as a reference material (Shimadzu DTA-50 analyzer). The density of the glass samples was measured using the Archimedes principle. The measurements were done using a digital balance and toluene as inert immersion liquid. The density was obtained from the relation

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Results and discussion

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XRD analysis

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The glass samples of neodymium doped lead bismuth borate were identified by XRD, the investigated glass samples as shown in Fig. 1. The X-ray diffraction pattern shows no sharp peaks indicating the absence of crystalline nature, and observed broad humps in the glass samples, characteristic of the amorphous phase at diffraction angles (2h) to be fully amorphous indicating that these glass samples are composed of glassy phase .

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FTIR spectral analysis

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Infrared spectroscopy studies were used to get essential information about the arrangement of the structural units of the glass samples. It is assumed that vibrations of characteristic groups of atoms in the glass network are independent of vibration of the other neighboring groups in the glass [21].

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The fundamental absorption bands of borate glasses are clear at three principal bands the first band, which occurs between 800 and 1200 cm1, is due to the B–O bond stretching of tetrahedral BO4 units. The second band that occurs between 1200 and 1600 cm1 is due to stretching vibration of B–O of trigonal BO3 units [22,23]. The third band is observed around 700 cm1 is due to the bending of various borate segments [24–26]. Infrared spectra [50 B2O3 – 25 PbO – 25 Bi2O3 – x Nd2O3] mol% glasses, with x = 0, 0.5, 1.0, 1.5 and 2.0 are shown in Fig. 2.

dðgm=cm3 Þ ¼ ½a=ða  bÞ  ðdensity of the tolueneÞ where ‘a’ is the weight of the glass sample in the air, ‘b’ is the weight of the glass sample when immersed in toluene and the density of the toluene is 0.86 (gm/cm3).

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Fig. 1. The X-ray diffraction pattern of neodymium doped lead bismuth borate glasses.

Fig. 2. Infrared spectra of [50 B2O3 – 25 PbO – 25 Bi2O3 – x Nd2O3] mol% glasses, with x = 0, 0.5, 1.0, 1.5 and 2.0.

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Infrared spectra collected from Bismuth lead borate sample (free from Neodymium) shows active peaks around 563,701, 820, 903,976, 1044,1224 and 1346 cm1. The band at 563 cm1 is due to Bi–O–Bi in BiO6 octahedral [27,28]. The band at 701 cm1 is due to bending vibration of B–O–B in BO3 triangles [23,29,30]. The band at 820 is due to vibration of Bi2O3 [1]. The B-O stretching vibration in BO4 units from di-borate groups was observed at 903 and 976 cm1 [31]. The absorption band at 1044 cm1 is probably due to the vibration of BO4 tetrahedra, which is present as tetraborate and diborate groups [32,33]. The absorption band at 1224 cm1 was assigned to B–O asymmetric stretching vibrations in BO3 unit from pyro- and ortho-borate groups [34,35]. The band at 1346 cm1 is assigned to the stretching vibrations of the B–O of trigonal BO3 units in metaborates, pyroborates and orthoborates [36]. Also from Fig. 2, it can be seen that no dramatic changes occur in the sharp form with the increasing Nd2O3 content in the glass. Addition of Nd2O3 content in the glass makes the band around 690–750 cm1 becomes sharper and shifted to higher frequency 665–770 cm1. The IR spectra can be deconvoluted to the component bands for each one to study the origin of this characteristic infrared symmetry. Fig. 3 represents the deconvolution in Gaussian bands of the spectrum for the glass containing [a] x = 0 mol%, [b] x = 1 mol% Nd2O3, respectively. The following method is used in the calculation of the fraction N4 of the four coordinated boron’s in the glass, where N4 ¼ ðconcentration of BO4 tetrahedraÞ=ðconcentration of BO3 triangle

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þ Concentration of BO4 tetrahedraÞ:

The obtained values are shown in Fig. 3 as the function of composition. To follow the evolution of the triangular and tetrahedral borate units in the studied samples we used the fraction of four-coordination boron atoms, as was defined previously [37,38]:

Fig. 3. Deconvoluted FTIR spectra of the 25 Bi2O3 – 25 PbO – 50 B2O3 – x Nd2O3 mol% samples using a Gaussian-type function for (a) x = 0 mol% and (b) x = 1 mol%.

N4 ¼

A4 A3 þ A4

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where A4 and A3 denote the areas of the BO4 and BO3 units. Fig. 4 shows the fraction of the four-coordinated boron atoms, N4, versus the Nd2O3 content of the glass samples. It is clear that the N4 decreases by adding Neodymium content. This is in agreement with the IR spectroscopy results, which detected a decrease in the intensity for four coordinated boron atoms BO4 than those three-coordinated ones of BO3 with increasing Nd2O3 concentration. The decrease of the BO4 groups with the addition of Neodymium oxide depends on the number of oxygen atoms and converted BO4 to BO3 groups and forms non-bridging oxygen (NBO). In addition, Neodymium oxide may enter the network as a modifier, which affects the probability of BO4 formation, i.e. increase of Nd2O3 concentration breaking up tetrahedral bonds of BO4 units and introduce coordination defects known as dangling bonds [39,40].

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DTA investigation

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DTA investigations of the glass transition temperature, Tg, are useful in identifying structural changes associated with compositional changes. The DTA curves of the different glasses have been measured at a heating rate of 30 °C/min. They exhibited an endothermic peak, which is characteristic of the glass transition region Tg, and the melting onset temperature, Tm, which may be the eutectic point of the glass samples. The effect of neodymium content on the thermal transition data for the investigated samples is shown in Fig. 5a and b as determined from the DTA traces. The endothermic peaks of the glass transition temperature and of the melting temperature are shifted gradually to higher temperatures by increasing Nd2O3 content. The values of glass transition temperatures, Tg, of the glass samples are seen to increase gradually as the neodymium oxide content is increased i.e., increase the structural connectivity as shown in Fig 5a. Moreover, Tg, depends on the BO3 and BO4 groups [41], which agree with IR results since BO4 decreases with increase in Nd2O3 content, which led to compactness of the structure and increasing the glass transition temperature. Fig. 5b shows the relation between Tm and Nd2O3 content. The reduced glass transition temperature Trg is used to evaluate the glass forming ability GFA [42] Trg = Tg/Tm as shown in Fig. 6. There is a clear correlation between the reduced glass transition temperature and the crystallization pattern. The reduced glass transition temperature Trg = Tg/Tm shows that, when Tg/Tm > 0.6, only surface crystallization is observed, while internal crystallization is easily observed in glass having Tg/Tm < 0.6 [43]. In view of that, the calculation of the reduced glass temperature shows that

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Fig. 4. The fraction of the four-coordinated boron atoms, N4, versus the Nd2O3 content of the glass samples.

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Fig. 5. The relation between (a) glass transition Tg and (b) melting temperature Tm and Nd2O3 content.

Fig. 7. The variation of density and molar volume of borate glass with increasing Nd2O3 content.

Fig. 6. The relation between the reduced glass transition temperature Trg and Nd2O3 content.

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the internal crystallization is observed in all samples and the glass samples with an increase in Nd2O3 content tend to decrease the internal crystallization.

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Density

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Density is a useful physical parameter used to investigate the degree of structure compactness, modification of the geometrical configurations of the glass network, change in coordination and variation of the dimensions of the interstitial holes [44]. The variation of density and molar volume of borate glass with increasing Nd2O3 content is shown in Fig. 7a and b. From this it can be seen that the density decreases and molar volume increases with increase of Nd2O3 content. Addition of Nd2O3 naturally increases the density of the glass system due to the increase of the molecular weight of oxide ions. However, practically the density decreases with increasing Nd2O3 contents. The decrease in the density with the gradual increase of Nd2O3 content may be due to the gradual increase of non-

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bridging oxygen attributed to changes occurred in the volume concentration of BO3 and BO4 units [45], which is consistent with the results of IR. Generally, the density and the molar volume show opposite behaviors. The increase of the molar volume with the addition of Nd2O3 contents attributed to increase in the number of Non-bridging oxygen (NBOS) [46].The change in molar volume depends on the rates of change of both density and molecular weight. However, the molecular weights increase with increase of Nd2O3 content due to addition of some massive Nd+3 ions and the density decreases this is accompanied by an increase in molar volume.

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Absorption spectra of Nd3+ doped in bismuth lead borate glasses are shown in Fig. 8. From Fig. 8, it can be seen that the transition energy levels depend on covalency and the asymmetry of Nd–O local structure among network former. It is seen that the absorption intensity of the observed bands increases with the increase of Nd2O3 content. The absorption bands of Nd3+ correspond to transitions from the 4 I9/2 ground state to various excited levels. These transitions were allocated by comparing the band positions in the absorption spectra with a standard for the Nd3+ ion [47–49]. The various spectroscopic transitions observed are as follows: 4F3/2 (877 nm), 4F5/ 2 4 S3/2 + 4F7/2 (745 nm), 4F9/2 (684 nm), 4H11/2, 2 + H9/2 (803 nm), (630 nm) 4G5/2 + 2G7/2(583 nm), 4G7/2 (526 nm) 4G9/2 (519 nm), 4 P3/2 (480 nm), 4K15/2 (460 nm) and 4P1/2 (435 nm). From Fig. 9, the intensity of transition shows a maximum and a minimum for glass sample containing 2 and 1 mol% Nd2O3, respectively. This indicates that the non-symmetric component of electric

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Opcal density (arb. Units)

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Wavelength (nm) Fig. 8. Absorption spectra of Nd3+ doped in bismuth lead borate glasses.

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field acting on Nd3+ ion is low for glass containing 1 mol% and high for 2 mol% of Nd2O3. The possible reason could be the formation of NBO’s around 2 mol% concentration of Nd2O3. The creation of nonbridging oxygen from bridging oxygen increases the symmetry of the bond to the neighboring network cation. The variation of the spectral profile of the transition, 4I9/2 ? 4F7/2, 4S3/2 is investigated and it indicates a higher covalency of the Nd–O bond for glass containing 2 mol% of Nd2O3. In addition, a lowest covalency is observed in glass with 1 mol% Nd2O3 [7]. The transition 4I9/2 ? 2P1/2 of Nd3+ ion in the absorption spectra is a characteristic of coordination of this ion. Generally, it is desirable in the construction of compact and efficient laser source pumped by diode laser [50–52].

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Conclusions

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The influence of neodymium oxide ions on some physical properties and structural changes in bismuth lead borate glasses has been investigated using X-ray diffraction, differential thermal analysis, density, molar volume, FT–IR and optical absorption spectra. The FTIR spectra conclude the dependence of the BO3/BO4 ratio on the Nd2O3 content. The decrease of the density and the increase of the molar volume with the addition of Nd2O3 contents attributed to increase in the number of Non-bridging oxygen (NBOS). The optical absorption results are indicating a higher covalency of the Nd–O bond for glass containing 2 mol% of Nd2O3. In addition, a lowest covalency is observed in glass with 1 mol% Nd2O3. The transition of Nd3+ ion in the absorption spectra at 435 nm is a characteristic of coordination of this ion. In addition, it is required in the construction of compact and efficient laser source.

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Please cite this article in press as: Kashif I et al. Effect of Nd2O3 addition on structure and characterization of lead bismuth borate glass2O3 addition on

Q1 structure and characterization of lead bismuth borate glass –>. Results Phys (2013), http://dx.doi.org/10.1016/j.rinp.2013.11.002