Optical properties of GeO2 glass and optical fibers

The optical properties of GeO(2) glass were investigated to clarify its potentiality as an optical fiber material. Glass samples were prepared by the flame hydrolysis and the melting techniques, and their Rayleigh scattering and infrared absorption properties were examined. Optical fibers composed of a pure GeO(2) core and an F-doped GeO(2) cladding were drawn to clarify the scattering loss characteristics. The Rayleigh-scattering intensity obtained from spectral loss measurements on the fibers agreed with that measured in bulk samples, and the intensity relative to that of SiO(2) glass was found to be approximately 3. These results suggest that a minimum loss of 0.15 dB/km is expected at a wavelength of 2 mum.     

Electron spin resonance and some electrical and optical properties of GeO2/SiO x thin films

Electron spin resonance measurements show a reduction in the spin density associated with unpaired electron dangling bonds of a mixed complex of co-evaporated GeO₂/SiO _x films compared with that of SiO _x films investigated under similar conditions. Unlike the behaviour of BaO/GeO₂ complex films, these samples show a decrease in the optical gap as the thickness increases for films of fixed compositions. However, it increases as the SiO percentage increases in films of the same thickness. D.C. measurements at low applied fields below 10⁵ V cm^–1 agree well with the spin density results.     

Dielectric dispersion in ZnF2-Bi2O3-TeO2 glass system

Dielectric constant , loss tan and ac conductivity of ZnF₂-Bi₂O₃-TeO₂ glasses with varying concentrations of Bi₂O₃ (from 5 to 20%) are studied as a function of frequency and temperature over moderately wide ranges. The dielectric breakdown strength for these glasses is also determined in air medium. From the analysis of these studies along with the IR spectra & DTA recordings of these glasses, the structural changes in ZnF₂-Bi₂O₃-TeO₂ glass system with change in the concentration of Bi₂O₃, are discussed.     

An investigation of the electrical,optical and DSC properties of a copper-phosphate glass composition

The variation of some physical properties of equimolar copper-phosphate glasses has been reported in the literature. The present work studied a 60 mol% P₂O₅-40 mol % CuO glass system using electrical conductivity, infrared absorption, optical absorption spectroscopy and differential scanning calorimetry. The results revealed an increase in the activation energy and the optical energy gap compared with that for equimolar P₂O₅-CuO, which could be attributed to the variation of reduced valence states of the copper ion in the process of glass formation. The relation between the a.c. electrical conductivity with frequency was found to be almost temperature-independent. Infrared measurement revealed similar trends to those reported for the same glass composition. DSC measurements showed endothermal peaks at 360, 520, 560 and 580 °C for this glass composition.     

Study of optical properties of GeO2 nanocrystals as synthesized by hydrothermal technique

The GeO₂ nanocrystals (α-quartz type structure) with β-phase are synthesized at relatively lower temperature by hydrothermal route using autoclave. All samples are characterized by XRD, FESEM, EDS, TEM, photoluminescence (PL) and UV–vis absorption spectroscopy techniques. Synthesized nanocrystals have uniform shape and uniform size distribution for a particular synthesis condition, which is about 30–300 nm depending on synthesis conditions. The XRD results indicate that grown GeO₂ crystals only shows peak related to α-quartz structure with lattice parameters a = 4.985 Å and c = 5.648 Å. UV–vis absorption spectroscopy measurements reveal the bandgap energies corresponding to the GeO₂ α-quartz structure. Synthesized nanocrystals are capable to emit strong blue light around 425–435 nm under excitation of 300 nm and 325 nm and consequently the as synthesized material can be used in integrated optical devices.     

The electrical properties of some cordierite glass ceramics in the system MgO-Al2O3-SiO2-TiO2

The a.c. dielectric breakdown and electrical resistivity of glass ceramics in the system MgO-Al₂O₃-SiO₂-TiO₂ have been studied using three sets of samples having different crystallinity contents. Standard a.c. (50 Hz) breakdown tests were performed at room temperature (18 °C) using planar disc specimens and hemispherically-ended brass contact electrodes. The breakdown process caused the formation of a breakdown channel which terminated at the specimen surface in a crater. The breakdown strength was independent of the rate of voltage rise, but decreased exponentially (60 to 10 kV mm^–1) with increasing specimen thickness. A high crystallinity content, good surface finish and a homogeneous microstructure yielded high breakdown strengths whilst poor microstructural development caused a reduction in breakdown strength. The breakdown mechanism is believed to be a combination of electronic, thermal and electromechanical processes.     

A study of the structural,electrical and optical properties of copper tellurium oxide glasses

The results of an investigation of some properties of CuO-TeO₂ glasses are reported. X-ray diffraction, differential scanning calorimetry and optical absorption measurements are discussed with respect to the compositions. D.c. conductivity is measured in the temperature range 293 to 453 K and discussed in terms of small polaron theory.     

Phase equilibria and transformations in the system Li2GeO3-Na2GeO3

The phase diagram has been determined using a combination of high temperature powder diffraction and quench furnace equilibration. Na₂GeO₃ forms a range of solid solutions which covers over half of the diagram at solidus temperatures (900 C) but whose extent is much more restricted at lower temperatures. Na₂GeO₃ solid solutions may undergo a variety of reactions on cooling, which include phase transformation and coherent precipitation.     

Pseudo-binary system Bi2O3-TeO2 in air

The phase equilibria in the pseudo-binary system Bi₂O₃-TeO₂ at 600° 950° C in air were examined by solid-state reaction techniques and X-ray powder diffraction method. Four pseudo-binary compounds appeared, i.e., -Bi₂O₃ type solid solution having a compositional range of (1-x)Bi₂O₃·xTeO₂ wherex=0 0.4 a new compound Bi₆Te₂O₁₅ which has an orthorhombic cell of a=2.27(4) nm, b=1.06(1) nm and c = 0.539(8) nm, 2Bi₂O₃ · 3TeO₂, and an unidentified phase Bi₂O₃·2TeO₂. The formation of the phase Bi₆Te₂O₁₅, in which all the Te ions are hexavalent, was confirmed by the thermogravimetry and by the Mössbauer spectra. The liquidus curves for whole system were determined by DTA method.     

A comparison of the optical properties of glass and of evaporated amorphous thin films of BaO-TeO2

Two series of glass and thin film specimens of BaO-TeO₂ were prepared. The optical absorption edges and infrared absorption spectra were investigated. It was found that the fundamental absorption edge is a function of BaO content in both kinds of films and that the absorption is due to indirect electronic transitions. The values of optical gap for blown films were greater than those of thin evaporated films, but the widths of the band tails were greater for the evaporated thin films, which were expected to be more disordered than the thin blown glass films.     

DC electrical conductivity of Na2O-ZnO-B2O3 glass system

The d.c. electrical conductivity of Na₂O-ZnO-B₂O₃ glass system has been measured as a function of temperature in the range of 350–600°K. The conductivity data show that the activation energy of Na⁺ ions is dependent on ZnO concentration. The results have been discussed in the light of the cluster model of glasses.     

Frequency-dependent electrical properties in the system SnO2-TiO2

The a.c. impedance response of polycrystalline ceramics Sn_xTi_-x1O₂ was studied in the air in the temperature range 298–1073 K. The impedance spectra were analyzed in terms of two proposed equivalent circuits involving both resistor and non-Debye constant phase element (CPE). The presence of CPE elements may be interpreted by diffusion phenomena. The results indicate a negligible contribution of grain boundary resistance to the total resistivity of the studied materials. The determined activation energy of the bulk conductivity of TiO₂ was compared with literature data. © 2001 Kluwer Academic Publishers     

Effects of GeO2 addition on physical and electrical properties of BaFe0.5Nb0.5O3 ceramic

This paper presents the effect of GeO₂ glass former on the physical and electrical properties of BaFe_0.5Nb_0.5O₃ (BFN) perovskite ceramics. The BFN powder was prepared by a conventional mixed-oxide method and the GeO₂ contents, ranging from 1 to 5 wt.%, were subsequently added to the calcined BFN powder. The mixtures were pressed and sintered to form dense ceramics. We showed that, with the addition of GeO₂, the maximum density was achieved at lower sintering temperature, approximately 200–225 °C lower than those required by the pure BFN ceramic. However, the densities of these GeO₂ doped BFN ceramics were slightly lower than those of pure BFN due to the occurrence of pores. We also found that the addition of GeO₂ reduces the dielectric loss at room temperature from 4.29 to 0.39–0.79 but the dielectric constant at room temperature decreased with the increased GeO₂ concentrations. With small amount of added GeO₂, ferroelectric property of BFN ceramics was also obtained, as confirmed by their hysteresis loops.     

A study on the electrical and optical characteristics of IGZO films

The electrical and optical properties of InGaZnO (IGZO) thin films were studied in the research. It was found that all the films deposited at room temperature exhibit amorphous structures. A better film quality was obtained at a lower pressure with sputtering ambiance. The RF power toward the IZO target was constant at 125 W; the RF power toward the Ga₂O₃ target varied from 0 to 70 W. A best IGZO film with corresponding resistivity, carrier concentration, and mobility is 7.94 × 10^?4 Ω-cm, 1.68 × 10²⁰ cm^?3, and 47 cm²/V-s, respectively. Due to the doping of gallium in the IGZO film, it led to a lower resistivity than that of the IZO film. A blue shift effect of the film was also observed in the doping of gallium to the IGZO film. The H₂ plasma effects toward the IGZO were also observed.     

Au thin films deposited on SnO2:In and glass: Substrate effects on the optical and electrical properties

We report on a detailed study on the optical and electrical properties of Au films made by sputter deposition onto glass substrates with and without transparent and electrically conducting layers of SnO₂:In. The Au films had thicknesses up to 10.7 nm and hence spanned the range for thin film growth from discrete islands, via large scale coalescence and formation of a meandering conducting network, to the formation of a more or less “holey” film. Scanning electron microscopy and atomic force microscopy demonstrated that the SnO₂:In films were considerably rougher than the glass itself, and this roughness influenced the Au film formation so that large scale coalescence set in at a somewhat larger thickness for films on SnO₂:In than on glass. Measurements of spectral optical transmittance and reflectance and of electrical resistance gave a fully consistent picture that could be reconciled with impeded Au film formation on the SnO₂:In layer; this led to pronounced “plateaus” in the near infrared optical spectra for Au films on SnO₂:In and a concomitant change from such two-layer films having a lower resistance than the single gold film at thicknesses below large scale coalescence to the opposite behavior for larger film thicknesses. Our work highlights the importance of the substrate roughness for transparent conductors comprising coinage metal films backed by wide band gap transparent conducting oxides.     

The electrical and optical properties of BiSiO2 cermet films

The electrical and optical properties of BiSiO₂ cermet films were studied. Using the temperature dependence of the resistivity of the cermet films and the dependence of the amount of oxidation of the fine bismuth particles on the volume percentage of bismuth, the three-dimensional percolation threshold composition was determined to be approximately 18 vol. % Bi.     

Film-thickness effects on the optical and electrical properties of Cu-GeO2 thin cermet films

The effect of film thickness on the optical and electrical properties of Cu-30 wt % GeO₂-70 wt % thin cermet films prepared by electron-beam deposition at about 10^–3 Pa and at a substrate temperature of 300 K is reported. The ultraviolet, visible and direct current (d.c.) conductivity results are analysed with the aim of determining the optical band gap,E _opt, the width of the band tails,E _e, and the d.c. thermal activation energy,E _a. It was found that the optical energy gap increases with increasing thickness and that the absorption was due to indirect transitions ink-space. The general feature of the absorption edge remains similar for both unannealed and annealed films, but annealing has the effect of decreasingE _opt. The d.c. conductivity results show thatE _a decreases with increasing thickness. From a knowledge ofE _opt andE _a, a probable model of the electronic band structure in Cu-GeO₂ thin films has been suggested.