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The transparent glasses with composition 30PbO–10GeO 2 –(60−x)SiO 2 −xNb 2 O 5 (mol%) (0 ≤ x ≤ 2.5) are prepared by conventional melt quenching technique. The amorphous nature of the prepared glasses is characterized by XRD. The spectroscopic studies such as optical absorption, FTIR, Raman spectra were carried out at room temperature on these glasses. Besides this electrical properties, like dielectric constant ε ' , loss tan δ , ac conductivity σ a c etc., were also investigated over a moderately wide range of frequency (10 3 –10 6 Hz) and temperature (30–300 °C). The optical absorption spectrum of the prepared glasses has exhibited absorption bands around 325 nm and 340 nm and these are due to the triplet – singlet electronic transition of Ge 2+ state presents in the glass matrix as conversion of GeO 2 into GeO is much easier rather than SiO 2 . From FTIR spectra of as prepared glasses, it is noticed that the intensity of octahedral NbO 6 structural units is found to increase up to 2 mol% of Nb 2 O 5 there after it is observed to decrease. It is also supported by Raman shift of NbO 6 structural units observed around 650 and 930 cm −1 . The analysis of electrical studies is also revealed that the conductivity of prepared glasses is found to increase gradually up to 2 mol% of Nb 2 O 5 beyond this concentration it is observed to decrease. When the spectroscopic investigations are coupled with electrical studies it is concluded that the glass samples doped with 2 mol% of Nb 2 O 5 are found to exhibit good semiconducting nature among the prepared glasses. Such glasses are suitable for fabrication of solid state devices. [ABSTRACT FROM AUTHOR]

In the present investigation we report the synthesis of a series of transparent glasses of composition 20Li 2 O 20PbO 45B 2 O 3 (15− x ) P 2 O 5 : x V 2 O 5 with eight values of x ranging from 0 to 2.5 mol%, and their characterization. X-ray diffraction (XRD) spectra reflected the amorphous nature of the glasses. Optical absorption, electron paramagnetic resonance (EPR) spectra and FTIR study of vanadyl ions in the present glass network have been analyzed. The optical absorption and EPR investigations have revealed that vanadium ions do exist in both V 4+ and V 5+ states and the redox ratio (V 4+ /V 5+ ) is observed to increase with the increase in concentration of V 2 O 5 . Dielectric properties viz., dielectric constant ε ′( ω ), loss tan δ , electrical moduli M ′( ω ), M ″( ω ), a.c. conductivity σ ac over an extensive scale of frequency and temperature have been investigated as a function of V 2 O 5 concentration. The dispersion of dielectric constant ε ′( ω ) with temperature has been interpreted by space charge polarization model. The dielectric loss and electrical moduli variation with frequency and temperature exhibited relaxation effects. These effects are ascribed to V 4+ ions. The a.c. conductivity of the prepared glasses is perceived to escalate with the hike in V 2 O 5 concentration whereas the activation energy for conduction exhibits a reverse trend. The conductivity mechanism is explained on the basis of polaronic transfer between V 4+ and V 5+ ions. The low temperature a.c. conductivity mechanism is elucidated by the quantum mechanical tunneling model. The growth in the values of dielectric parameters with raise in the concentration of V 2 O 5 is due to V 4+ ions which act as modifiers. The investigation of these results has indicated that at higher concentrations of V 2 O 5 , the VO 2+ ions in the glasses were present in octahedral sites with tetragonal compression and belong to C 4v symmetry. [ABSTRACT FROM AUTHOR]