2009
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PublicationArticle Amorphous to crystalline phase transition in glassy Se65Te20Ag15 alloy(2009) R.S. Tiwari; D. Kumar; N. MehtaIn the present work, the amorphous to crystalline phase transition of chalcogenide glass Se65Te20Ag15 has been studied using differential scanning calorimetric (DSC) measurements. The heating rate dependence of crystallization peaks has been used for the determination of activation energies of glass transition (Eg) and crystallization (Ec). Different non-isothermal methods have been used for this purpose. Other useful kinetic parameters such as the order parameter (n), the numerical factor of crystallization mechanism (m) and the frequency factor (Ko) of the rate constant (K) have been also determined.PublicationArticle Effect of Sb and Sn additives on the activation energies of glass transition and crystallization in binary Se85Te15 alloy(2009) N. Mehta; K. Singh; S. KumarCalorimetric measurements have been performed in glassy Se75Te15M10 (M=Sb, Sn) alloys to study the effect of Sb and Sn additives on the kinetics of glass transition and crystallisation in glassy Se85Te15 alloy. Activation energy of glass transition (Eg) and the activation energy of crystallisation (Ec) have been determined using different non-isothermal methods. An excellent agreement is observed in the values of Ec and Eg for all the non-isothermal methods used in the present study. The composition dependence of the activation energies of glass transition and crystallisation processes shows that the value of Eg is higher in case of Sn additive while the value of Ec is higher in case of Sb additive. The results are explained in terms of Pauling's concept of average heat of atomisation and mean atomic weights of ternary alloys, respectively.PublicationArticle Effect of lithium-ion irradiation on the crystallization kinetics of glassy Se98In2(2009) H. Kumar; N. Mehta; K. Singh; N.S. SaxenaDifferential scanning calorimetry (DSC) has been used to study the crystallization kinetics of glassy Se98In2 both before and after irradiation of the alloy with high-energy (50 MeV) lithium ions. After the ion-irradiation, significant changes in the kinetic parameters of crystallization of the glass were observed. The results are explained in terms of a model involving irradiation-induced defects.PublicationArticle Composition dependence of UV-visible and MID-FTIR properties of Se98-xZn2Inx (x = 0, 2, 4, 6 and 10) chalcogenide glasses(2009) Abhay Kumar Singh; Kedar SinghThe UV-VIS absorption spectra of thin film of Se98-xZn2Inx (x = 0, 2, 4, 6 and 10) chalcogenide glasses were measured in the wavelength range of 200-1100 nm by using spectrophotometer. It is observed from UV-VIS absorption measurements that the optical energy gap (Eg) decreases with In content and it found a minimum for the Se92Zn2In6 system. The refractive index (n), extinction coefficient (k), real dielectric constant (') imaginary dielectric constant (''), absorption coefficient () are evaluated maximum for the Se92Zn2In6 composition. However, FTIR spectra were recorded in the wavenumber range 4000-400 cm-1. The FTIR recorded spectrum was shown to be a broad spectrum with increasing transmission in the MID (6-25 m) infrared region. The MID-IR spectrum transmittance percentage was also found to be considerably high for the Se92Zn2In6 system. © 2009 Taylor & Francis.PublicationArticle Further MN rule for thermally activated high field conduction in bulk samples of glassy Se100-xSbx alloys(2009) N. Mehta; V.S. Kushwaha; A. KumarIn the present paper, we report the observation of the Meyer-Neldel rule (MNR) in thermally activated high field conduction in bulk samples of glassy Se100-xSbx alloys. We have investigated Meyer-Neldel rule by two different approaches. In first approach, the temperature dependence of d.c. conductivity is studied at different electric fields without changing the composition of the glassy system. In the second approach, the composition itself varies at a particular electric field. We found that the conductivity obeys the Meyer-Neldel rule as the pre-exponential factor depends on activation energy. We also found a strong correlation between pre-factor σ00 and Meyer-Neldel energy in both cases. The observation of the correlation between pre-factor σ00 and Meyer-Neldel energy can be described by multiple excitations stimulated by phonon energy as described by Yelon and Movaghar. © 2009 Elsevier Ltd. All rights reserved.PublicationArticle On the glass transition phenomenon in Se-Te and Se-Ge based ternary chalcogenide glasses(2009) N. Mehta; K. Singh; A. KumarThe present paper reviews the results of non-isothermal differential scanning calorimetry (DSC) measurements on some ternary glassy systems of Se-Te and Se-Ge chalcogenide alloys for evaluation of activation of glass transition. The activation energy of glass transition (Eg) is calculated using Kissinger's relation, which is basically derived for amorphous to crystalline phase transition. The results show that Eg values obtained from Kissinger's relation are in good agreement with the Eg values which are obtained using Moynihan's relation based on the concept of thermal relaxation. This proves the applicability of Kissinger's relation for determination of activation energy of glass transition. © 2009 Elsevier B.V. All rights reserved.PublicationArticle Correlation between Meyer-Neldel rule and phase separation in Se98-xZn2Inx chalcogenide glasses(2009) Abhay Kumar Singh; Neeraj Mehta; Kedar SinghThe present work reports the observation of Meyer-Neldel rule for the thermally activated crystallization of glassy Se98-xZn2Inx (0 ≤ x ≤ 10) alloys. We have observed a strong co-relation between the pre-exponential factor K0 of rate constant K(T) of crystallization and activation energy of crystallization Ec in the present case. This indicates the presence of compensation effect for the non-isothermal crystallization process in the present glassy system, which is explained in terms of phase separation of the present alloys due to flaw bonds of these amorphous solids. © 2008 Elsevier B.V. All rights reserved.PublicationArticle Optical and FTIR properties of Se93-XZn2Te5InX chalcogenide glasses(2009) Abhay Kumar Singh; Neearj Mehta; Kedar SinghIn this work, we report the optical properties of bulk Se93-XZn2Te5InX (X=0, 2, 4, 6 and 10) chalcogenide glasses. Refractive index, extinction coefficient, real dielectric constant (ε′), imaginary dielectric constant (ε″), absorption coefficient (α) and energy band gap were obtained from analysis of common range (250-1100 nm) UV/Visible transmittance spectrum. Besides, transmission percentages were obtained from FTIR spectra in wave number range 4000-400 cm-1.The concentration dependence structural phenomena have been explained with help of average coordination 〈z〉. © 2009 Elsevier B.V. All rights reserved.