Search

Multi-component glass ceramics composition Na2O−PbO−Bi2O3−SiO2doped with different concentrations of Fe2O3as nucleating agent were characterised by XRD, SEM (scanning electron microscope) and DTA (differential thermal analysis) techniques. Optical absorption, EPR, FTIR and Raman studies are also carried out on these glass ceramics. Absorption bands observed at about 457, 489, 678 and 820 nm are the characteristics of Fe3+ions whereas the band observed at about 964 nm is due to Fe2+ions. EPR studies suggested that Fe3+ions entered in the lattice as tetragonally distorted octahedral symmetry or rhombic sites at low concentration of Fe2O3, whereas at higher concentration of Fe2O3(beyond 1 mol%), the super exchange type of interactions between multivalency iron ions begin to dominate. FTIR and Raman spectra have revealed the behaviour of various structural units in the glass ceramic matrix. The analysis of these spectroscopic studies indicates that iron ions do exist in Fe3+and Fe2+state. [ABSTRACT FROM AUTHOR]

Multi-component CaF2-Bi2O3-P2O5-B2O3 glasses doped with different concentrations of V2O5 were crystallised and characterised by XRD, SEM, EDS and DTA. Spectroscopic studies were carried out. The XRD and SEM studies indicated that the samples contain different crystalline phases. Optical absorption and EPR studies on the samples have indicated that a considerable proportion of vanadium ions are present in the V4+ state in addition to the V5+ state and the redox ratio seems to be increasing with an increase in the concentration of the nucleating agent V2O5. FTIR and Raman studies revealed that depolymerisation of phosphate chains, with the formation of cross linkages such as P-O-B, P-O-Bi and P-O-V, occurs in the glass-ceramic matrix. Quantitative analysis of results of the spectroscopic studies further indicated that concentration of VO2+ gradually increases with increasing concentration of the nucleating agent V2O5. Therefore, the glass-ceramics with higher concentrations of V2O5 exhibit a semiconducting nature. [ABSTRACT FROM AUTHOR]

Pure and tungsten oxide doped ZnF2-Bi2O3-P2O5 glass-ceramics are prepared by the melt quenching and heat treatment techniques. These samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron dispersive spectroscopy (EDS) and differential thermal analysis (DTA) techniques. The X-ray diffraction and the scanning electron microscopic studies have revealed the presence of BiPO4, α-Zn3(PO4)2, α-Zn(PO3)2, Zn3(PO4)2, WOF4, WOPO4, γ-Bi2WO6, Bi2W2O9, microcrystalline phases in these samples. FTIR and Raman studies exhibit bands due WO4 and WO6 units along with conventional phosphate groups. The optical absorption and electron spin resonance (ESR) spectra of present glass-ceramics indicate the co-existence of both W5+ and W6+ ions. The analysis of dielectric properties (dielectric constant, loss tan δ, a.c. conductivity) over a range of frequency and temperature suggests a gradual increase in semi conducting character with increase in the concentration of WO3. The studies on dielectric breakdown strength indicated the lowest insulating strength for 5.0 mol% of WO3 in the present samples. [ABSTRACT FROM AUTHOR]

Abstract: Transparent glasses 20ZnF2–40Bi2O3–(40− x)GeO2:xCoO; 0⩽ x ⩽1wt% are prepared by melt quenching technique. The amorphous nature of the samples is characterized by X-ray diffraction (XRD) and differential thermal analysis (DTA). Spectroscopic studies like optical absorption, FTIR, Raman and dielectric parameters (ε′, loss tan δ, conductivity σac over a wide range of frequency and temperature as well as dielectric breakdown strength at room temperature) of these samples have been carried out. Optical absorption data has revealed that the bismuth radicals, observed in pure sample C0, are combined with cobalt ions with increase in concentration of CoO. Further, Co2+ and Co3+ ions occupy octahedral positions at larger dopant concentrations of CoO. From FTIR and Raman studies the coordination of germanium is changed from GeO4 to GeO6 with increase in the concentration of CoO. Dielectric parameters such as dielectric constant ε′, loss tan δ, a.c. conductivity σac are increased and activation energy for a.c. conduction is decreased and hence opens the glass network with the increase of divalent cobalt ion concentration; which is also confirmed by decrease in glass transition temperature (Tg ) and band gap energy (Eg ). Density of defect energy states (EF ) is explained with quantum mechanical tunneling (QMT) model. [Copyright &y& Elsevier]

Abstract: Transparent glasses 40Sb2O3–20ZnF2–(40− x)GeO2:xCuO, and 40Bi2O3–20ZnF2–(40− y)GeO2:yCuO with x =0, 0.6 and 0≤ y ≤1wt% were prepared by melt quenching technique and were characterized by XRD and differential thermal analysis. Spectroscopic studies like optical absorption, FTIR, Raman, EPR and dielectric parameters (such as ɛ′, loss(tan δ), and σ ac) were carried out to examine the modifier and dopant effect on zinc germanate glass network. Optical absorption and EPR data have revealed that the environment of Cu2+ ions is more ionic in bismuth series rather than antimony glasses. Reduced bismuth ions have been found in pure and at lower concentration of dopant in Bi2O3 mixed glasses, which are useful for IR amplifications. FTIR and Raman spectra have indicated the conversion of GeO4 to GeO6 structural units by forming cross linking bonds like Bi–O–Ge, Ge–O–Cu, etc., and open the glass network with integration of Bi2O3 and CuO doping. It is also confirmed by decreasing T g and E g values. The temperature dependence of dielectric parameters at different frequencies was interpreted in terms of structural changes in the glass network. [Copyright &y& Elsevier]