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Spectroscopic and Optical Properties of the VO2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system
Swapna,G. Upender,V. Sreenivasulu,M. Prasad 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.8
Studies such as optical absorption, Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, Electron paramagnetic resonance (EPR) spectroscopy and Differential scanning calorimetry (DSC) were carried out on VO2+ ion doped TeO2-TiO2-ZnO-Nb2O5 glass system. Raman and FTIR spectra of the glasses revealed the presence of [TeO3], [TeO4] and [NbO6] structural units in the glass network. The Urbach energy (E), cut-off wavelength (c), optical band gap (Eopt), optical basicity () and electron polarizability () of the glasses were determined from optical absorption studies. The density (), molar volume (Vm), oxygen molar volume (Vo) and refractive index (n) were also measured. Spin-Hamiltonian parameters were calculated from the EPR studies. When Nb2O5 was increased at the expense of ZnO, the density, optical band gap and Urbach energy of the glasses increased, and the electronic polarizability and optical basicity decreased. The EPR spectra clearly showed that vanadium was in the glass as VO2+ and occupied octahedral sites with tetrahedral compression. Spin-Hamiltonian parameters gk and g? decreased as Nb2O5 content increased in the glass. The glass transition temperature (Tg) also increased with increasing Nb2O5 content in the glass.
M. VENKATESWARLU,G. UPENDER REDDY,D. VENKATA LAKSHMI 한국산업응용수학회 2018 Journal of the Korean Society for Industrial and A Vol.22 No.4
This paper examined the MHD and thermal behavior of unsteady mixed convection flow of a rotating fluid in a porous parallel plate channel in the presence of Hall current and heat source. The exact solutions of the concentration, energy and momentum equations are obtained. The influence of each governing parameter on non dimensional velocity, temperature, concentration, skin friction coefficient, rate of heat transfer and rate of mass transfer at the porous parallel plate channel surfaces is discussed. During the course of numerical computation, it is observed that as Hall current parameter and Soret number at the porous channel surfaces increases, the primary and secondary velocity profiles are increases while the primary andsecondaryskinfrictioncoefficientsareincreasesatthecoldwallanddecreasesattheheated wall. In particular, it is noticed that a reverse trend in case of heat source parameter
Suresh Sripada,D. Esther Kalpana Rani,G. Upender,P. Gayathri Pavani 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.5
Titanium boro tellurite glasses in the xB<sub>2</sub>O<sub>3</sub>−(90−x) TeO<sub>2</sub> + 10TiO<sub>2</sub> (where x = 0 to 50 mol%) system were prepared by using the conventional melt-quenching technique. Glass transition temperatures were measured with differential scanning calorimetry (DSC) and found to be in the range of 300 - 370 ℃. The Raman spectra showed a cleavage of the continuous TeO<sub>4</sub> (tbp) network by breaking of the Te-O-Te linkages. The relative transition of TeO<sub>4</sub> − groups to TeO<sub>3</sub> − groups is accompanied by a change in the oxygen coordination of the boron from 3 to 4 (BO<sub>3</sub> <sup>−</sup> to BO<sub>4</sub> <sup>−</sup>). The impedance plots Z▼(┺) versus Z▽(┺) for all the glass samples were recorded and found to exhibit a single circle. The AC conductivity of all glass samples was studied in the frequency range from 100 Hz to 1 MHz and in the temperature range from room temperature (RT) to 375 ℃. The AC conductivity decreased by about one order in magnitude with increasing B<sub>2</sub>O<sub>3</sub> content. The conductivity was found to be on the order of 10<sup>−4.5</sup> to 10<sup>−6</sup> (┯-cm)<sup>−1</sup> at 375 → and 1 MHz for 10 mol% and 50 mol% B<sup>2</sup>O<sup>3</sup> contents, respectively. The relaxation behavior in these glass samples is discussed based on the complex modulus and impedance data.