Anup Kumar

Synthesis and Reactions of Tetrakis(4-Methoxyphenoxo)titanium(IV)

Abstract The compound of the composition Ti(0C6H40Me-4)4 (I) has been isolated by reacting titanium tetra-chloride with 4-methoxy-phenol in 1:4 molar ratio in benzene and characterised on the basis of elemental analyses, conductance, molecular weights, IR and NMR spectral studies. Reactions of (I) with α -hydroxy-aldehydes and ketones and some nitrogenous bases such as 1,10-phenanthroline and 2,2-bipyridylhave also been investigated.

Calorimetric study of tellurium rich Se-Te-Sn glasses

We report the calorimetric study of amorphous Se30Te70-x Snx alloys for x= 0, 1.5, 2.5, 4.5 in terms of kinetic parameters. The DSC curves recorded at four different heating rates are analyzed to determine the transition temperatures, activation energy, thermal stability, glass forming ability. The crystallization process has been investigated using Kissinger, Matusita, Augis and Bennett, and Gao and Wang models. Various kinetic parameters have been calculated for a better understanding of the growth mechanism. The glass transition temperatures Tg, onset crystallization Tc, peak crystallization Tp, and melting temperature Tm are found to increase with the increase in Sn content. The system under investigation is found to be thermally stable for at lower at% of Sn. The values of parameters HR, Hw, and S indicate that Glass forming ability (GFA) decays with an increase in Sn content.

Investigative Study of Optical Parameters of Se80.5Bi1.5Te18-yAgy Thin Films

The optical constants, like absorption coefficient (α), optical band gap (Eg) and refractive index (n), in Se80.5Bi1.5Te18-yAgy (y= 0, 1.0 and1.5) thin films are calculated using well known Swanepoel’s method in the spectral range of 600-2000 nm. The optical band gap has been estimated by using Tauc’s extrapolation method and is found to increase with increase in Ag content. The present results shows that the large value of nonlinear refractive index and good transparency of these thin films will make them a very promising materials for optical integrated circuits in the optical communication systems.

Effect of Sn on the optical band gap determined using absorption spectrum fitting method

We report the preparation and the optical studies on tellurium rich glasses thin films. The thin films of Se30Te70-x Snx system for x= 0, 1.5, 2.5 and 4.5 glassy alloys prepared by melt quenching technique are deposited on the glass substrate using vacuum thermal evaporation technique. The analysis of absorption spectra in the spectral range 400nm–4000 nm at room temperature obtained from UV-VIS-NIR spectrophotometer [Perkin Elmer Lamda-750] helps us in the optical characterization of the thin films under study. The absorption spectrum fitting method is applied by using the Tauc’s model for estimating the optical band gap and the width of the band tail of the thin films. The optical band gap is calculated and is found to decrease with the Sn content.

Effect of compositional variation on the electrical properties of Se-Te-Bi-Ag glassy alloy

In this paper we have studied the effect of Ag addition on electrical properties of Se80.5Bi1.5Te18-yAgy (y = 1.0, 1.5 and 2.0 at. %) glassy system by using digital picometer (Keithley, model 6487) in the voltage range 0-300V. I-V study reveals that the glassy alloys under study exhibit ohmic behavior at low voltage and non-ohmic at high voltage. The field dependence studies for pellets reveal the ohmic nature of current for voltage less than 60V and non-ohmic nature of current for voltage greater than 60V. At higher voltage, greater than 60V, thermal effects come into plays which result in an increase in electrical conductivity. The d.c. conductivity is found to increase with an increase in Ag content. The conduction mechanism is discussed in terms of Poole-Frenkel conduction mechanism. The linearity of the plots between ln(I) and V1/2 shows that the conduction mechanism in the higher voltage range is of Poole-Frenkel type.

Nonlinear optical properties of quaternary amorphous Se80.5Bi1.5Te18−yAy (A = Sb, Ag) thin films

Effect of Sb and Ag addition on the optical constants of Se80.5Bi1.5Te18−yAy (A = Sb, Ag and y = 2.0 at. %) thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index increases with an increase in Sb or Ag content and the absorption coefficient is also found to increases with increase in optical energy. Whereas the optical band gap decreases with an increase in Sb content and increases with an increase in Ag content. Hence, the present results reveals that the addition of Sb and Ag produce remarkable change on the nonlinear optical properties of the thin film.

Dispersion parameters and optical band gap in Se80.5Bi1.5Te18−ySby amorphous thin films

The dispersion parameters such as single-oscillator energy (E0), dispersive energy (Ed) and static refractive index (n0) of Sb doped quaternary thin films are studied in terms of Wemple-DiDomenico (WDD) single oscillator approach. Optical band gap (Eg) is determined from Tauc’s extrapolation method and is found to decrease with an increase in Sb content. Tanaka’s relation is found valid for the films under study.The dispersion parameters such as single-oscillator energy (E0), dispersive energy (Ed) and static refractive index (n0) of Sb doped quaternary thin films are studied in terms of Wemple-DiDomenico (WDD) single oscillator approach. Optical band gap (Eg) is determined from Tauc’s extrapolation method and is found to decrease with an increase in Sb content. Tanaka’s relation is found valid for the films under study.

Frequency dependence of dielectric constants of Ag doped Se-Bi-Te system

The effect of Ag addition on dielectric properties of Se80.5Bi1.5Te18-yAgy (y= 0, 1.0 and 1.5) glassy system. Dielectric relaxation studies are important to understand the nature and origin of dielectric losses, which in turn may be useful in the determination of structure and defects in solids. dielectric parameters (dielectric constant e′(ω) and dielectric loss e″(ω)) are studied in the frequency range 1 kHz-50 kHz over the temperature range 300K – 365K, using parallel impedance measurements.

Theoretical Investigations of Electronic Properties of Se{sub 82-x}Bi{sub x}Te{sub 18} Thin Films

The effect of Bi on the structural and optical properties of Se82−xBixTe18 glassy alloys is studied, theoretically. Cohesive energy is calculated by using chemical bond approach and is found to decrease with increasing Bi content. Optical band gap of thin films is calculated by Shimakawa’s relation. The optical band gap decreases with increase in Bi content.

Optical Properties of Bi Doped Amorphous Se‐Te Thin Films

Effect of Bismuth (Bi) doping on the optical constants of Se‐Te thin films, prepared by thermal vacuum evaporation technique, is investigated using Swanepoel method. The optical constants i.e. refractive index (n), film thickness, absorption coefficient and optical energy gap are calculated from the transmission spectra. It has been found that refractive index decreases with wavelength, for all compositions and the absorption coefficient increases with increase in optical energy. On the other hand the optical band gap is found to decreases with increase in Bi content.