Nanocrystalline glass ceramics: Structural, physical and optical properties

Journal of Molecular Structure 1081 (2015) 211–216

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Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc

Nanocrystalline glass ceramics: Structural, physical and optical properties Satwinder Singh, K. Singh ⇑ School of Physics & Materials Science, Thapar University, Patiala 147004, India

h i g h l i g h t s  Effect of transition ions on nanocrystalline phase formation in glass ceramics.  Correlation of structure and properties of glass ceramics.  Higher content of ZnO increases the optical band gap.

a r t i c l e

i n f o

Article history: Received 4 August 2014 Received in revised form 8 October 2014 Accepted 9 October 2014 Available online 16 October 2014 Keywords: Glass ceramics Structure Nanocrystalline Transition cations

a b s t r a c t Four different transition metals contained nanocrystalline glass ceramics are synthesized by melting and quenching technique. The transition metal oxides play as former, modifier or both the roles depending on their oxidation states, field strength and covalent characteristics. The optical band gaps are observed in the range of 3.2–5.5 eV. The presence of nano-crystalline phases dominates the optical band gap. The softening temperature (Ts) is mainly affected by the residual glass in glass ceramics. These glass ceramics can be used as shielding materials for nuclear waste. Ó 2014 Elsevier B.V. All rights reserved.

Introduction Glasses and glass ceramics are an important class of materials and exhibit very attractive properties [1,2]. These materials are being used in aerospace industry, telecommunications, photonics, solid oxide fuel cells, waste materials management and medical applications, etc. [3]. Structurally, glassy materials lack the long range order. However, they maintain the short range order at the local level. The lack of grain boundaries makes most of the glasses to be transparent, which leads to lots of applications. The local structure of the glasses, many times can be changed according to the desired properties by employing some compositional changes or by some other means, like by developing some crystalline phases by controlled heat treatment of the glass i.e. glass ceramics. The presence of crystalline phase in the glass matrix significantly changes the molecular structure and subsequently the other properties of glass. The properties of the glass ceramics depend upon the glass matrix composition and also on the kind and amount of the crystalline phase present in the glass matrix [4]. Glasses and ⇑ Corresponding author. Tel.: +91 1752393130; fax: +91 1752393005. E-mail address: [email protected] (K. Singh). http://dx.doi.org/10.1016/j.molstruc.2014.10.018 0022-2860/Ó 2014 Elsevier B.V. All rights reserved.

glass ceramic materials generally absorb electromagnetic energy in the ultraviolet and infrared region due to the electronic transitions in interior molecules and molecular vibrations, respectively. Widely varying optical characteristics of the glass and glass ceramics are further tailored when elements from transition series are included in the glass composition. In general, these properties are associated with variable oxidation state of the transition elements [5–7]. Actually, the different oxidation states of the elements exhibit different field strengths. The changes in field strength of the cation causes modification to the glass network and properties [8]. In addition to this, the field strength of the cation affects the polarization of its neighboring ions, which in turn affects their interaction with light. Glasses, usually consist of three components, namely, glass formers, modifiers and intermediates. The incorporation of the network modifier, like alkali and alkaline earth metal oxides, into the glass, leads to a wide range of different structural configuration possibilities along with unique physical properties [3]. Network modifiers create non-bridging oxygens (NBOs) in the glass network. The amount of these negatively charged NBOs plays a crucial role in determining the optical, thermodynamic and structural properties of glass and glass ceramics [9]. Not only alkaline and alkaline earth metal oxides, but oxides

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of the transition elements also act as a modifier or former depending upon their valence state, amount and initial composition [10,11]. Many studies have reported the effect of different transition metals on the formation of the glass and glass ceramics and their properties [12–14]. Apart from this, lots of studies have been carried out to investigate the optical properties of nanocrystalline ZnO, TiO2, Fe2O3 and MnO2. However, the nano particles of these transition elements required some capping agents to prevent the agglomeration for their application. So, in the present case, high contents of TiO2, ZnO, MnO2 and Fe2O3 were taken purposely, so that, they can act as nucleating agents and increase the tendency to form nanocrystalline phases in the glassy matrix. In this situation, glass matrix will act as a capping agent. The objective of the present study is to investigate the effect of different transition metal oxides on structural, physical, thermal and optical properties of nanocrystalline phases contained glass ceramics. Additionally, the selection of these transition metal oxides is based on their initial valence states. The transition metal cations are taken by their decreasing valence states such as Ti4+, Mn4+, Fe3+ and Zn2+ in four different compositions. Moreover, their field strength decreases with increasing covalent bond characteristic. Therefore, it is worthwhile to study the effect of their valence states, change in covalent characteristics and electronegativity on glass formation, physical, thermal, structural and optical properties. In the present study, glass ceramic samples with composition 45SiO2–25CaO–10Na2O–5P2O5–15TO, where TO = TiO2, MnO2, Fe2O3 and ZnO were prepared using the melting and quenching technique. The structural investigations of the as prepared samples were carried out using X-ray diffraction, Fourier Transform Infrared Spectroscopy (FTIR) and dilatometry. The optical parameters were calculated from the absorption spectra obtained using UV– visible spectroscopy. Observed characteristics were correlated in the light of field strength, polarization power of the transition metal cations and the structural modifications by the addition of transition elements. Materials and methods Glass samples were prepared by melting and quenching technique. Raw materials in the form of oxides and carbonates were taken as SiO2, CaO, Na2CO3, P2O5, TiO2, MnO2, Fe2O3 and ZnO (Loba Chemie, P99% Pure). The compositions (mol%) and their label are given in Table 1. The chemicals were grounded in an agate mortar pestle for 1 h in an acetone medium. After grinding, the mixtures were put in a recrystallized alumina crucible and melted at 1550 °C in a programmable electric furnace. The melt was held at this temperature for 1 h to get bubble free and homogeneous melt. This melt was air quenched between two thick copper plates. As quenched samples were crushed into the powder form for the characterizations. The density of the quenched samples was measured by Archimedes’ principle in xylene using a sensitive microbalance. The least count of the balance was 0.01 mg. Density is the simplest measurable physical quantity of any solid material. It gives valuable information about the structure of the given material. The density of the samples is calculated as follows:

Table 1 Compositions of the samples along with labels.

qSample ¼

SiO2

CaO

Na2O

P2O5

TiO2

MnO2

Fe2O3

ZnO

15-T 15-M 15-F 15-Z

45 45 45 45

25 25 25 25

10 10 10 10

5 5 5 5

15 0 0 0

0 15 0 0

0 0 15 0

0 0 0 15

ð1Þ

where qSample is the density of the sample, qx is the density of xylene at 30 °C, wa is the weight of the sample in air and wx is the weight of the sample in xylene. Density of xylene is 0.863 g/cc at room temperature. The amorphous nature of the samples was studied using X-ray diffraction patterns on PANalytical X’Pert PROX-ray diffractrometer with Cu Ka radiations (k = 1.54 Å). During the experiment the step size was 0.017° and scan rate was 3° min1. Infrared spectroscopy can be employed to acquire deeper insight of the structure of the glasses. Information about the competitive roles played by each oxides in the glass network was investigated by analyzing the FTIR spectra of the present samples. Perkin ElmerSpectrum-RX-IFTIR spectrometer was used to record Fourier Transform Infrared (FTIR) in the range 450–4000 cm1. Powdered samples were mixed with KBr and the recorded spectrum was normalized to the spectrum of KBr. The softening temperature of all glass ceramics was measured by horizontal type dilatometer (DIL402PC, Netzsch) with 5 °C/min heating rate in the air. UV–visible absorption spectra of the samples were obtained using Hitachi U-3900H UV–visible spectrophotometer in the spectral range of 200–800 nm. To obtain the absorption spectra, the powder samples were dissolved in 38% HCl, which was diluted further 10 times before sonication for 20 min. Contribution of HCl part was nullified for each sample by normalizing it to the base dilute HCl spectra. Results and discussion Density and molar volume Apparent densities of the glass ceramics are given in Table 2. The density of the samples depends on the densities of its individual constituent [3]. However, in the case of glasses and glass ceramics, many other factors also marginally influence the final density of the sample. Some of these factors include the thermal history of the sample, measurement temperature, crystallization, creation of NBOs, the field strength of the modifier, etc. Molecular weights of the intermediate oxides, in the present compositions, follows as TiO2 < ZnO < MnO2 < Fe2O3. The density of the samples should have followed the similar trend, but 15-Z was found as an exception in the present study, as shown in Table 2. The density of the 15-Z is greater than the 15-M sample. This can be explained on the basis of the fact that the addition of divalent cations (Zn2+) forms higher NBOs than other intermediate oxides. It is reported that the breaking of the glass network by the modifier increases the compactness of the glass. Secondly, the XRD patterns clearly indicate that the 15-Z sample has a higher degree of crystallinity as compared to the 15-M sample. As crystalline ordering increases in any system, the compactness of the network also increases and leads to an increase in the density of the system [15]. 15-F, containing iron oxide, is the densest sample among the present series. On the other hand, 15-T sample due to the lowest molecular weight in all the intermediate oxides has the lowest density. The structure of the glass and glass ceramic samples can be explained in terms of molar volume as it represents the spatial distribution of the ions that form the structure. Molar volume can be calculated using the following equation:

Vm ¼

Label

wa  qx wa  wx

M

q

ð2Þ

where M is the molecular weight and is the density of the sample. Vm represents the volume in the space occupied by one mole of the sample. The molar volume depends on M and q, so as molecular weight and density of the samples among the present series do not

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S. Singh, K. Singh / Journal of Molecular Structure 1081 (2015) 211–216 Table 2 Physical parameters for the samples. Sample name

Molecular weight (g/mol)

Density (g/cc)

Molar volume (cc/mol)

Excess volume (cc/mol)

Oxygen molar volume (cc/mol)

Oxygen packing density (mol/L)

15-T 15-M [17] 15-F [17] 15-Z

66.33 67.39 78.31 66.56

2.75 2.83 3.02 2.98

24.12 23.81 25.93 22.34

1.21 1.14 1.28 0.08

13.40 13.23 13.30 13.54

74.63 75.59 75.20 73.86

vary monotonically, hence, we get a non-linear variation in Vm with transition metals. Excess volume (Ve) is a quantity derived from the molar volume of the sample and molar volumes of the individual oxides. Ve was calculated as follows:

Ve ¼ Vm 

X xi V m ðiÞ

ð3Þ

i

where Vm(i) is the molar volume of ith oxide, xi is the mole fraction of the oxide present in the composition. Additionally, the oxygen molar volume (Vo) values and oxygen packing density (OPD) were also calculated using the following relations:

Vm Vo ¼ P xi ni OPD ¼

No: of oxygen atoms per unit formula unit Vm

ð4Þ

ð5Þ

where ni is the number of oxygen atoms in ith oxide. All calculated values are summarized in Table 2. The excess volume varies in a similar manner as the molar volume. Fig. 1 shows the variation in molar and excess volume of the samples. 15-Z glass ceramic exhibit lowest excess volume. It might be ascribed due to higher NBOs and more compactness in the glass network. Maximum excess volume is observed in the 15-F sample. As XRD (in the next section) indicates the formation of FeOFe2O3 phase in the glass matrix. This crystalline phase exhibits very large unit cell (inverse spinel structure) with a lower packing density might be a possible reason to have the higher excess volume of this particular sample. X-ray diffraction analysis XRD patterns of 15-T, 15-M, 15-F and 15-Z are shown in Fig. 2. XRD patterns show the presence of some crystalline peaks. It clearly indicates that all the samples are glass ceramic (nanocrystalline) in nature. However, the degree of crystallinity is different for different samples. In addition to this, it also indicates that higher contents of transition metal oxides, irrespective of their chemical nature, prevent the glass formation. The crystallite sizes

Fig. 1. Variation in molar and excess volume of the samples.

Fig. 2. XRD patterns of the glass ceramic samples (o-SiO2, #-Zn2SiO4, +-Fe3O4, ⁄-CaMn2Si3O9, /-CaMnO3, D-NaO3, X-Na2CaSiO4).

of the crystalline phases are calculated using Scherrer formula. These crystalline phases are nano-crystalline and crystallite sizes vary from 20 to 50 nm. The formation of these crystalline phases is due to the presence of some intermediate oxides those might have acted as nucleating agents. However, the small amount of heavy metal oxides usually act as nucleating agents [16]. In case of 15-F, Fe2O3 converts into nanocrystalline Fe3O4, as reported in our previous publication [17]. Based on different crystalline phases formation, it can be observed that Ti4+ may not have participated as a direct nucleating agent in case of 15-T. XRD peaks for sample 15-T were assigned to SiO2 (ICDD No. 01-082-1556) and Na2CaSiO4 (ICDD No. 00-024-1069). Two peaks in the XRD pattern of 15-M composition are assigned to CaMn2Si3O9 (ICDD No. 00-042-0548) and CaMnO3 (ICDD No. 00-050-1746). XRD pattern of 15-F exhibited the crystalline peaks corresponding to Fe3O4 (ICDD No. 01-075-0033) [17]. Whereas, 15-Z exhibited SiO2 (ICDD No. 01-082-1556) and Zn2 (SiO4) (ICDD No. 01-083-2270) nanocrystalline phases. Lahl et al. [18] reported that initially SiO2

Fig. 3. Absorption spectra of 15-T glass ceramic.

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segregated as a crystalline phase during heat treatment, with the passage of time some other cations diffused in SiO2 and formed the stable crystalline phases. Additionally, in case of the 15-T sample, TiO2 might act as glass former and could not form any crystalline phase having TiO2 as an integral part of crystalline phase. It might be possible, when it forms only TiO4 units in the glass network. However, this particular sample shows two absorptions at 347 nm and 262 nm in the UV–visible spectrum as shown in Fig. 3. It is associated with some phase separation in the glass. In case of MnO2 contained glass ceramics two crystalline phases are formed. These crystalline phases have manganese in two oxidation states, i.e. Mn4+ (CaMnO3) and Mn3+ (CaMnSi3O9). It means Mn4+ transformed to Mn3+ during the glass formation. On the other hand, during reduction of Fe3+ in 15-F might have given very small amount of NBOs. Contrary to 15-T, 15-M and 15-F, the ZnO fully acted as a modifier in 15-Z glass ceramic. The nature of these transition metal cations in the glass network is explained further in the next sections. FTIR analysis Generally, the position of the IR bands in the spectra confirms the presence of particular bonds. On the other hand, the shape and the shift in these IR bands gives valuable information about the changes in the structure with the respective changes in the composition. Major IR band with highest intensity and broadness is present in all the samples centered at around 1017 cm1 with small changes according to the composition. Other bands with medium and low intensity in the FTIR spectra of the samples were observed 457–487, 560–591 704–740 cm1. FTIR spectra of 15-T and 15-Z samples are presented in the Fig. 4. The spectra of the present samples specify the role of each oxide contained in the composition. Transmission bands of 15-Z sample are diffused to the most extent among the other samples of the present series. As mentioned in the previous section, ZnO is most likely to act as a network modifier in the present series and alters the glass structure significantly. Due to this alternation, the bond parameters no longer remain sharply defined. As a consequence, the IR bands appear to be diffused and broad instead of sharp band. In FTIR spectra of 15-Z samples, the transmission band at 487 cm1 is attributed to stretching vibrations of Zn–O bonds [19]. Transmission band at 742 cm1 is a band characteristic of Si–O–Si tetrahedral bond. Two IR bands of medium intensity at 561 and 593 cm1 may be attributed to the vibrational modes of P–O and Zn–O bonds respectively [20,21]. IR band at 471 cm1 is related to the bending vibrations of Si–O–Si vibrations. This band is present in the FTIR spectra of all samples. However, in the spectra of 15-T sample

this band is slightly shifted to lower wavenumber and at the same time has higher intensity as compared to the other samples. This is because of the fact that the IR band due to Ti–O–Ti bonds also exhibit itself at the same position. Similarly, in the literature, vibrations of Ti–O bonds are reported at 590 cm1, 525 cm1 and 722 cm1 [22]. Si–O bonds and P–O bonds also give their characteristic signatures at quite similar positions. FTIR spectra of 15-M and 15-F samples have been discussed earlier [17]. In 15-F sample IR band at 578 cm1 has highest intensity compared to band at similar position for other samples. This is because IR band at this position is also related to Fe3+–O bonds, in addition to the vibrations due to P–O bonds. Hence, due to overlapping of the IR bands of different bonds, isolated peaks could not be obtained. Consequently, broad bands are observed in the spectra of these samples.

Dilatometric softening analysis In contrast to crystalline materials, glasses and glass ceramics do not show melting at a particular temperature. Instead, glasses and glass ceramics show a transition from solid material to a melt, through a rubber like behavior. This phenomenon is called softening of the material. The softening temperature (Ts) gives a good approximation about the strength of the glass network. The softening temperatures of the glass ceramics are given in Table 3. The presence of nanocrystalline phases in glass ceramics could not affect the softening temperature of glass ceramic, since their melting temperatures are much higher. Hence, the softening temperature of the present glass ceramic samples is related to the softening of the residual glass present in the glass ceramics. The softening temperature of glass depends on the bond strengths and the cross links. It can be clearly observed that 15-Z glass ceramic has minimum softening temperature. This supports that ZnO creates the maximum number of NBOs as compared to other transition metal oxides in the glass ceramics. It indicates that ZnO acts as a strong network modifier in 15-Z glass ceramic. 15-M has a higher softening temperature than 15-Z. This can be explained by the fact that manganese played dual role as network modifier and former. Manganese in Mn4+ state can act as a network former, while in Mn3+ state, it acts as a glass modifier. So, network forming tendency of MnO2 increase the softening temperature of the 15-M sample. TiO2 may have acted only as a glass former in 15-T glass ceramic. So, it should have had even much higher softening temperature than any other, but Ti4+ ions caused phase separation [23–25]. This phase separation causes the decrease in the strength of the glass network and may lead to lowering the softening temperature. Interestingly, 15-F glass ceramic has highest softening temperature (Table 3). Although, it has a tendency to act as intermediate oxide, however, it seems that in the present case, Fe2O3 has not participated actively in the glass formation. Only a fraction of Fe2O3 might have entered the glass network and created some NBOs. Remaining amount of Fe2O3 got converted to Fe3O4 (FeOFe2O3) [17]. Secondly, the small fraction of oxygen, created during Table 3 Optical band gap (Eopt), Urbach energy (EU), refractive indices (n), average molar reflection (Rm), polarizability (am), metallization parameter (M) and softening temperature for all samples.

Fig. 4. FTIR spectra of 15-T and 15-Z glass ceramic.

Label

15-T

15-M

15-F

15-Z

Optical band gap (Eopt) (eV) Urbach energy (EU) (eV) Refractive index (n) Average molar reflection Rm (cm3 mol1) Polarizability am (cm3  1024) Metallization parameter, M Softening temperature (°C)

4.21 0.26 2.11 12.91 5.12 0.46 720

3.55 0.33 2.26 13.76 5.45 0.42 704

3.20 0.17 2.35 15.59 6.18 0.40 753

5.54 0.36 1.92 10.55 4.18 0.47 633

S. Singh, K. Singh / Journal of Molecular Structure 1081 (2015) 211–216

Fe2O3 to Fe3O4 transformation, might have provided a relatively oxygen-rich environment to the melt. This type of atmosphere may have given extra oxygen sites for Ca2+ and Na+ cations to get neutralized. Consequently, it might have prevented modification to the glass network by alkali and alkaline earth metal cations. It may be the possible reason that 15-F glass ceramic has a higher softening temperature as compared to other glass ceramics. Optical band gap and Urbach energy In case of amorphous materials, the absorption coefficient exhibits a sharp increase just before the band gap. These may be caused by the transitions of the electrons from the excited oxygen [26]. The relation between absorption coefficient and the incident photon energy is given by Davis and Mott [27] by the following relation:

"

ahm ¼ b

hm  Eopt hm

n # ð6Þ

where b is a constant, a is the absorption coefficient, hm is the photon energy and Eopt is the optical band gap. n is the index, whose value depends on the type of the transition taking place. In the present case, the optical band gap of the samples was calculated from the absorption edges using Tauc’s plots by plotting (ahm)2 vs. energy (hm) as shown in Fig. 5. Optical band gaps of all the glass ceramics fall in the insulator category. These nanocrystalline glass ceramics can be used as a shielding material in nuclear-related applications. The highest band gap is observed in 15-Z followed by 15-T glass ceramics. The lowest optical band gap is observed for 15-F glass ceramics. In the present samples, it is very difficult to make out the contribution of the different crystalline phases embedded in the glass matrix towards optical band gaps. In contrast to crystalline solids, glass ceramics have a range of bond angles and distances. This sort of distribution of bond characteristics leads to exponential tails in the density of states of the solids. Consequently, localized energy states appear in the electronic band structure of the solid. These localized states enhance the probability of the excitation of the electrons even below the band gap when light energy of the sufficient energy is incident on the material. Hence, absorption spectra of the glass ceramic solids exhibit exponential tails just below the absorption edge, which are called Urbach tails. Urbach tails are characterized by a parameter EU (Urbach energy) [28]. Absorption coefficient (a(m)) of the material is related to the Urbach energy as aðmÞ ¼ b expðhm=EU Þ, where b is a constant called tailing parameter. Urbach energy was calculated by taking the reciprocal of the slope of the linear

215

portion of the ln(a) vs. energy. The value of Urbach energy is minimum for 15-F sample. This can be explained on the basis of crystallinity, the 15-F sample has a maximum degree of crystallinity as shown in Fig. 2. Crystallinity increases the ordering in the network leading to less defects and hence low Urbach energy. The 15-Z sample has maximum value of Urbach energy, indicating that it has maximum disordered structure. That is obvious as divalent Zn2+ creates maximum NBOs compared to the other samples, and hence, have created maximum disorder in the structure. It is reported that the presence of higher number of NBOs decreases the band gaps. However, in the present glass ceramic samples could not follow any trend as shown in Table 3. It might be possible due to presence of crystalline phases, which influence the optical band gap properties as well as Urbach energy. Refractive index and average molar reflection The refractive index of the solid is determined by the interaction of light with the electrons of its constituent atoms. According to Dimitrov and Sumio [29], the refractive index (n) of a solid is related to the optical band gap of the material as:

n2  1 ¼1 n2 þ 2

rffiffiffiffiffiffiffiffi Eopt 20

ð7Þ

There are so many factors that affect the refractive index of the glasses like polarizability of the first neighbor ions coordinated with the anion, the field strength of the cation, co-ordination number, NBOs, electronic polarizability of the oxide ion, crystallization, etc. [30,31]. Polarizability of the samples was calculated from average molar reflection (Rm) of the prepared samples. Average molar reflection of the samples can be calculated as:

Rm ¼

 2  n 1 Vm n2 þ 2

ð8Þ

The quantity (n2  1)/(n2 + 2) is called the reflection loss. The polarizability, am (cm3  1024) was calculated using the relation:

am ¼



 3 Rm 4pN

ð9Þ

The values of refractive indices, average molar reflection and polarizability are given in Table 3. Increase in the electron density or polarizability of the ions results in an increase in the refractive index. Variation in the refractive index is accompanied by the corresponding variations in polarizability and molar reflection. Refractive index increased up to 15-F sample and then decreased for 15-Z sample. In general, the refractive index increases with increasing covalent character of the bonds, which further depends on the difference in the electronegativities of the bond forming atoms. The percentage covalent character of the bonds increased as Ti– O < Mn–O < Fe–O. Whereas, at the end of the transition series (Zn) covalency decreases for Zn–O bond, which in turn decreases the refractive index. The variation in the refractive index is in good agreement with the variation in covalent character of the bonds. Although, the formation of partial crystalline phases may affect the refractive index. However, the covalent character and polarizability have been the dominating factors to determine the refractive index of the present samples. Metallization criterion (M) To predict the metallic or insulating behavior of the solid, metallization criterion can be used. Metallization criterion M, is given as:

M ¼1 Fig. 5. Tauc’s plot for the glass ceramic samples.

Rm Vm

ð10Þ

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For Rm = Vm, the Lorentz–Lorenz Eq. (8) gives an infinite value of refractive index. According to metallization criterion, the necessary and sufficient condition for a material to be metallic in nature is Rm/Vm P 1, and for non-metallic behavior Rm/Vm < 1. The calculated values of M for all samples in given in the Table 3. For all the samples M < 1 indicates their insulating behavior. All these glass ceramic samples are predicted to be poor conductors. Conclusion Four different transition element oxides contained samples are prepared by melt and quench technique. All the samples are nanocrystalline glass ceramics in nature, in which every transition metal oxide plays different roles and initiate to form different nanocrystalline phases. The density of the samples increases with an increase in molecular weight of transition metal oxides except 15-Z. The 15-Z glass ceramic exhibit minimum excess volume, average molar reflection, polarizability, refractive index and softening temperature with maximum values of optical band gap (5.54 eV) and Urbach energy. On the other hand, the 15-F sample shows a completely opposite trend for these properties. FTIR bands for 15-Z sample are most diffused indicating that ZnO changed the structure of glass to maximum extent. Values of metallization criterion for all the samples suggest their poor conducting nature. These glass ceramics might be used as shielding materials for nuclear waste management. Acknowledgements Authors are thankful to UGC – India for financial support under the scheme MANF for minority students under the award letter number F1-17.1/2012-13/MANF-2012-13-SIK-PUN-11203/(SA-III/ Website). References [1] C.A. Harper, Handbook of ceramics, Glasses and Diamonds, McGraw-Hill Professional, USA, 2001.

[2] H. Jan, The Technology of Glass and Ceramics: An Introduction, Elsevier Science Ltd, New York, 1983. [3] J.E. Shelby, Introduction to Glass Science and Technology, Royal Society of Chemistry, Cambridge, UK, 2005. [4] G. Nagarjuna, N. Venkatramaiah, P.V.V. Satyanarayana, N. Veeraiah, J. Alloys Comp. 468 (2009) 466–472. [5] I. Ardelea, M. Peteanu, S. Filip, D. Alexandru, J. Magn. Magn. Mater. 157–158 (1996) 239–240. [6] M. Elisa et al., Opt. Quantum Electron. 39 (2007) 523–531. [7] A. Terczyn´ska-Madej, K. Cholewa-Kowalska, M. Ła˛czka, Opt. Mater. (Amst) 33 (2011) 1984–1988. [8] G. Kaur, O.P. Pandey, K. Singh, J. Non Cryst. Solids 358 (2012) 2589–2596. [9] M. Abdel-Baki, F. El-Diasty, Curr. Opin. Solid State Mater. Sci. 10 (2006) 217– 229. [10] N. Krishna Mohan, K. Sambasiva Rao, Y. Gandhi, N. Veeraiah, Phys. B Condens. Matter 389 (2007) 213–226. [11] K. Sharma, S. Bhattacharya, C. Murali, K.G. Bhushan, G.P. Kothiyal, Appl. Surf. Sci. 258 (2012) 2356–2361. [12] A.M. Abdelghany, F.H. ElBatal, M.A. Azooz, M.A. Ouis, H.A. ElBatal, Spectrochim. Acta A: Mol. Biomol. Spectrosc. 98 (2012) 148–155. [13] M. Farouk, J. Non Cryst. Solids 402 (2014) 74–78. [14] A. Terczyn´ska-Madej, K. Cholewa-Kowalska, M. Ła˛czka, Opt. Mater. (Amst) 32 (2010) 1456–1462. [15] W. Holand, G. Beall, Glass Ceramic Technology, The American Ceramic Society, USA, 2002. [16] D. Bahadur, N. Lahl, K. Singh, L. Singheiser, K. Hilpert, J. Electrochem. Soc. 151 (2004) A558–A562. [17] S. Singh, K. Singh, J. Non Cryst. Solids 386 (2014) 100–104. [18] N. Lahl, D. Bahadur, K. Singh, L. Singheiser, K. Hilpert, J. Electrochem. Soc. 149 (5) (2002) A607–A614. [19] R.N. Gayen, R. Bhar, A.K. Pal, Physics 48 (2010) 385–393. [20] Q. Williams, E. Knittle, J. Phys. Chem. Solids 57 (1996) 417–422. [21] R. Viswanatha, T.G. Venkatesh, C.C. Vidyasagar, Y.A. Nayaka, Arch. Appl. Sci. Res. 4 (1) (2012) 480–486. [22] T. Bezrodnaa, T. Gavrilkoa, G. Puchkovskaa, V. Shimanovskaa, J. Baranb, M. Marchewkab, J. Mol. Struct. 614 (2002) 315–324. [23] P.E. Doherty, D.W. Lee, R.S. Davis, J. Am. Ceram. Soc. 50 (1967) 77–81. [24] P. Schultz, J. Am. Ceram. Soc. 59 (1976) 214–219. [25] W. Zdaniewski, J. Mater. Sci 8 (1973) 192–202. [26] J. Tauc, J. Amorphous and Liquid Semiconductors, Springer, US, 1974, http:// dx.doi.org/10.1007/978-1-4615-8705-7. [27] N.F. Mott, E.A. Davis, Electronic Processes in Non-Crystalline Materials, Clarendon, Oxford, 1979. [28] F. Urbach, Phys. Rev. 1324 (1953). [29] V. Dimitrov, S. Sumio, J. Appl. Phys. 79 (1996) 1736. [30] S. Buchner, M.B. Pereira, N.M. Balzaretti, Opt. Mater. (Amst) 34 (2012) 826– 831. [31] M. Abdel-Baki, F. El-Diasty, J. Solid State Chem. 184 (2011) 2762–2769.