Electrical conductivity of ion-exchanged oxide glasses

Bulk glasses in the system Na₂O-CaO-Al₂O₃-B₂O₃-SiO₂ have been subjected to a sodium silver exchange reaction. The application of a suitable combination of electric field and temperature brings about switching to a high conducting state (HIE). The critical electric field,E _c, has a value in the range 2 to 20 V cm^–1 andE _c values decrease as a function of temperature. The resistivity in the HIE state is of the order of 10 cm and the activation energy is 0.01 eV. Wagner's asymmetric polarization cell measurements show that the conductivity is ionic in nature. No switching is observed in the case of glasses subjected to a sodium copper exchange reaction carried out on these glasses at 525 ° C for 12h. This is ascribed to the microstructure exhibited by such exchanged samples which consists of copper-rich droplet phases dispersed within a copper-deficient matrix. The rather large inter-droplet separation makes it difficult for the copper-rich phase to grow to its percolation limit.     

Electrical conductivity in iron-containing oxide glasses

The electrical properties of silicate, borate, phosphate and tellurite glasses containing iron are reviewed. The highest electrical conductivity has been observed in iron-tellurite glasses. The problem of the structure and influence of different glass modifiers on the electrical conduction of iron-containing glasses is discussed.     

Mechanical properties of glass fibres containing aluminium dispersoids

Glass fibres containing metallic aluminium dispersoids up to 7.5 at% AI have been made using ceramic bushings. The metallic granules have diameters ranging from 5 to 40 nm. A new technique based on strength-strain regression analysis has been used to determine the Young's moduli of the glass fibres. The Weibull parameters have been evaluated by both the graphical regression (GRE) and maximum likelihood (MLE) techniques. Fracture studies have also been carried out. The presence of aluminium particles increases the Young's modulus of the fibres but reduces the strength. The latter arises due to the metallic particles acting as stress concentrators within the glass matrix.     

Electric-field-induced bleaching of ion-exchanged glasses containing copper nanoparticles

Combined action of a dc electric field and elevated temperature on ion-exchanged glasses containing copper nanoparticles leads to the dissolution of nanoparticles in a sample region near the positive electrode. As a result, the sample, which was initially red, becomes transparent in the near-surface region under the positive electrode, this effect being readily observed by the naked eye. An important feature of this phenomenon, which can be of interest for practical applications, is the local dependence of the optical density in the surface layer of the sample on the shape and the surface relief of the electrode. This dependence is manifested by the formation of an image of the electrode surface (facing the sample) on the glass surface. Conditions necessary for the manifestation of these phenomena are discussed.     

Electrical conductivity of lanthanum oxide based composites containing carbon nanofibers

We have measured the electrical conductivity of lanthanum oxide based composite materials containing different concentrations of carbon nanofibers as additives. The conductivity has been shown to increase sharply (by two orders of magnitude) at carbon nanofiber contents from 2 to 3 wt % owing to the formation of a three-dimensional network of nanofibers in the bulk of the composite. Particular attention has been paid to the morphology of the particles of the constituent components of the composites and to the chemical and phase compositions of the matrix material.     

Electrical conductivity of zinc-barium phosphate glasses

A series of binary and ternary zinc-barium phosphate glasses was prepared, their densities were measured and their electrical properties were studied. A linear dependence of density with BaO content was observed in barium phosphate glasses while a breaking point in the linearity of the density curves occurs at about 40% ZnO concentration for the zinc-barium phosphate glasses. The d.c. conductivity measurements show that the activation energy is increased when P₂O₅ is replaced by BaO or ZnO, respectively. In the ternary glasses the activation energy appears to be relatively unaffected when BaO is replaced by ZnO, but at approximately 40%ZnO, there is a rise in the value of activation energy. Such a pronounced change in density and activation energy could be due to the change in the coordination of ZnO in this region. The linear log -1/T curves and also the value of _o suggest that the conduction mechanism in these glasses is similar to those in many other oxide glasses that have been investigated.     

Electrical conductivity and ESR of lithium borate glasses containing mixed transition metal oxides

Electron spin resonance, optical spectra and d.c. electrical conductivity of 2Li₂O · 3B₂O₃ glasses doped with V₂O₅ and CuO were investigated. Spin Hamiltonian parameters of transition metal (TM) ions have been determined. The theoretical optical basicity _th of these glasses has been calculated and related to the spin-Hamiltonian parameters of TM ions. The variation of electrical conductivity with composition has been explained.     

Electrical conductivity of field-assisted ion-exchanged glass with molten PbCl2 salt

Field-assisted ion-exchange was carried out between soda-lime-silica glass tubes and molten PbCl₂ at 823 K for 2 h under constant potential of 12 V. The field-assisted ion-exchange leads to the formation of a lead-exchanged layer underneath the glass surface. The influence of the exchange on the bulk d.c. and a.c. electrical conductivity was investigated and compared with that of the glass before ion-exchange. The d.c. conductivity of the exchanged glass showed an activation energy higher than that of the glass before ion-exchange. The higher activation energy was attributed to the lower mobility of lead cations in the exchanged layer in comparison with that of sodium cations. The a.c conductivity of the exchanged glass showed an increase in the dielectric constant and a decrease in the dielectric loss. These findings suggest that lead cations enter the glass network in modifying positions in the exchanged glass. The results also support the data previously obtained that one lead cation from the molten PbCl₂ replaced two sodium cations from the glass.     

Electrical conductivity and optical properties of gamma-irradiated niobium phosphate glasses

A detailed study of the d. c. electrical conductivity and the optical absorption spectra as a function of gamma-irradiation doses for prepared (20 mole% Nb₂O₅ –80 mole% P₂O₅) glass system is presented. The temperature dependence on the d. c. electrical conductivity measurements is studied over the temperature range from room temperature to 573 K. The induced changes in the d. c. electrical conductivity caused by different doses of gamma irradiation (0–16 Mrad) were studied. The electrical conductivity, , and the activation energy, E, values were found to be sensitive to the gamma-ray doses. The optical absorption spectra were measured in the wavelength range from 200 to 1100 nm at different -doses, in the range from 0 to 28 Mrad. The obtained results are analysed assuming optical absorption by indirect transition. Values of the absorption coefficient, , the optical energy gap, E _opt, and the width of the band tail, E, are found to be -irradiation dose dependent.     

Strengthening of ultrafine PM aluminium using nano-sized oxycarbonitride dispersoids

Composites consisting of ultrafine aluminium, mainly reinforced by in situ nano-sized oxycarbonitride dispersoids, were prepared by mechanical alloying followed by a simple press and sintering method. The mechanical alloying process was performed under atmospheres with different amounts of ammonia. Even when small amounts of ammonia were used, the gas was able to decompose at room temperature, with N incorporated into the aluminium powder. The sintered compact properties were strongly influenced by the amount of N incorporated into the powders during milling, with an almost linear trend for some of these properties.     

Electrical conductivity of thermally grown titanium oxide films

TheV-I characteristics of thermally grown titanium oxide films on titanium are described and are explained using a model for current transport in the films.