Search

Abstract Glass ceramics of the composition PbO Al 2 O 3 TeO 2 GeO 2 SiO 2 doped with CoO (ranging between 0 and 1.0 mol %) were prepared by melt quenching technique followed by heat treatment. The techniques such as XRD, SEM, EDS and DTA were employed for the characterization of the prepared samples. Conventional spectroscopic studies viz., optical absorption, photoluminescence, FTIR and Raman were also performed on these samples. The optical absorption spectra of the titled glass ceramics exhibited two principal absorption bands, one at about 594 nm and the second one consisting of multiplets with the meta centre at about 1455 nm ascribed to the 4A 2 (4F) → 4T 1 (4P) and 4A 2 (4F) → 4T 1 (4F) transitions of tetrahedrally coordinated Co2+ ions, respectively. Besides these, the spectra also exhibited two feeble bands at about 532 and 643 nm which are the characteristics of octahedrally coordinated Co2+ and Co3+ ions, respectively. Using Tanabe Sugano diagram the crystal field splitting parameter Dq, Racah parameters B, C and nephelauxetic ratio, β were evaluated for Co2+ ions. The photoluminescence spectra of the titled glass ceramics have exhibited two broad emission bands at 628 and 870 nm ascribed to 4T 1 (4P) → 4A 2 (4F) and 4T 1 (4P) → 4T 2 (4F) tetrahedral transitions of Co2+ ions, respectively. FTIR and Raman spectra of the titled samples exhibited various asymmetrical and symmetrical vibrational bands due to viz., silicate, germanate, PbO 4 , PbO 6 , AlO 6 , TeO 4, TeO 3 and CoIII O vibrations in the glass ceramic matrix. The spectroscopic investigations on the titled glass ceramics have revealed that if CoO is present in small quantities the cobalt ions predominantly occupy the octahedral sites in the glass network, whereas the tetrahedrally coordinated Co2+ ions are found to increase if the concentration of nucleating agent CoO is gradually increased up to 1.0 mol%. As a result the degree of depolymerization of the glass network decreases which in turn enhances its rigidity with increasing the concentration of nucleating agent CoO. From these investigations we report that the glass ceramics doped with 1.0 mol% of CoO are suitable for insulating devices as well as for photonic devices. Graphical abstract Optical absorption spectra of PbO Al 2 O 3 TeO 2 GeO 2 SiO 2 : CoO glass ceramics and the pre-heated samples viz. , Co2, Co10. Image 1 Highlights • PbO Al 2 O 3 TeO 2 GeO 2 SiO 2 : CoO glass ceramics were prepared by melt quenching and heat treatment. • Prepared samples were characterized by XRD, SEM, EDS and DTA. • Absorption bands of the samples indicated the cobalt ions exist in Co2+ and Co3+ state. • Photoluminescence spectra of the samples exhibited emission bands at 628 and 870 nm. • Samples doped with 1.0 mol% of CoO are suitable for insulating and photonic devices. [ABSTRACT FROM AUTHOR]

Multi-component glass ceramics with composition 29PbO–5Al 2 O 3 –1TeO 2 –10GeO 2 – (55–x) SiO 2 doped with different concentrations of CuO (0 ≤ x ≤ 1.0 mol %) were synthesized by melt quenching technique and subsequent heat treatment. These glass ceramics were characterized by X–ray diffraction, scanning electron microscope, differential thermal analysis, optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman studies. The absorption spectra of these glass ceramics exhibited a broad absorption band in the range 650–950 nm which is ascribed to 2 B 1g → 2 B 2g octahedral transition of Cu 2+ ions. A feeble band around 364 nm is also identified in the samples doped with CuO up to 0.6 mol% as being due to charge transfer between the two oxidation states Cu 2+ and Cu + of copper ions. The EPR spectrum recorded at room temperature exhibited a strong resonance signal at g ⊥ = 2.072 and a shallow quadruplet at about g ǁ = 2.401. FTIR and Raman spectra of the titled samples provide significant information about various structural units viz ., silicate, germanate, PbO 4 , PbO 6 , AlO 6 , TeO 4 and TeO 3 that are present in these ceramic matrix. Analysis of the spectroscopic investigations reveals that with an increase in the concentration of CuO up to 0.6 mol% copper ions do exist in Cu 2+ and Cu + states and they act as modifiers and net work formers respectively. Therefore, glass ceramic sample contains 0.6 mol% of CuO is favorable for memory switching action. [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]