Electronic conductivity in zinc iron phosphate glasses

The electrical properties of (40−x)ZnO–xFe₂O₃–60P₂O₅ (x = 10, 20, 30 mol%) glasses were measured by impedance spectroscopy in the frequency from 0.01 Hz to 4 MHz and the temperature range from 303 to 473 K. It was shown that the dc conductivity strongly depends on the Fe₂O₃ content and Fe(II)/Fe_tot ratio. The increase in dc conductivity for these glasses is attributed to the increase in Fe₂O₃ content from 10 to 30 mol%. With increasing Fe(II) ion content from 6% to 17% the dc conductivity increases. This indicated that the conductivity arises mainly from polaron hopping between Fe(II) and Fe(III) ions suggesting an electron conduction in these glasses. By applying scaling on conductivity data measured at different temperatures, single master curve was obtained for each glass. On the other hand, deviation from the master curve at high frequencies was observed for glasses with different compositions. This deviation originates from a various mobility of charge carriers in different glass structures. Raman spectra showed the change of structure, from metaphosphate to pyrophosphate, with increasing Fe₂O₃ content from 10 to 30 mol%.     

Band gap in cadmium zinc phosphate glass

The band gap in cadmium zinc phosphate glass samples with composition 35 mol% CdO-5 mol% ZnO-60 mol% P₂O₅ has been determined by absorption and photoconduction measurements. The two values of the band gap are nearly the same within the experimental error. The photoconductive band gap shows a slow decrease with an increase in the applied field. The results have been discussed in terms of the energy band model for non-crystalline solids.     

Electrical properties and glass transition temperature of multiwalled carbon nanotube/polyaniline composites

Polyaniline (PANI) was synthesized and doped with 0, 2, 4 and 16 wt.% of pure and functionalized multiwall carbon nanotubes (MWCNTs) by “in-situ” polymerization. Measurement of temperature dependence of electrical resistivity showed a reduction in the resistivity of the composites at all temperatures. The reduction was increased by increasing the wt.% of MWCNTs. This decrease was more for the composites containing functionalized MWCNTs and was more prominent for temperatures below 150 K. The glass transition temperature (T_g) of the pure and doped PANI was measured using electrical resistivity measurements. It was observed that by increasing the amount of functionalized MWCNTs in PANI, its T_g increases. Temperature dependence of resistivity of pressed pure PANI showed that by increasing the pelletization pressure, the bulk electrical resistivity decreased but the T_g increased.     

Fabrication of Sn-doped zinc phosphate glass using a platinum crucible

The authors investigate the structural change of a ZnO–P₂O₅ sintered matrix for the preparation of SnO-doped zinc phosphate (SZP) glass using a platinum crucible. Heat treatment of zinc oxide and ammonium phosphate at 800 °C causes the formation of a Zn₂P₂O₇-like species, which is effective in preventing damage to the platinum crucible. Although the thermal property of the glass was affected by added Al₂O₃, Al₂O₃ hardly affects the quantum efficiency of the SZP glass phosphor. This process is important for the fabrication of contamination-free phosphate glass using ammonium phosphate as a starting material.     

Electrical conductivity studies on carbon black loaded ethylene butylacrylate polymer composites

In this work we studied the electrical properties of carbon black mixed into ethylene butylacrylate copolymer, using impedance spectroscopy, in the frequency range from 100 Hz to 100 kHz and over the temperature range from 150 to 360 K. A series of samples was prepared with several filler contents, below and above the percolation threshold, which was calculated using direct current conductivity measurements. For concentrations below the critical concentration the negative temperature coefficient in resistivity effect is observed, and for concentrations above that threshold the positive temperature coefficient in resistivity effect is present. The dielectric response was analyzed using complex permittivity or modulus formalisms, depending on the concentration of filler in the polymer matrix. Havriliak–Negami model was used to fit the experimental results.     

Sensitizing Sm emission by non-radiative energy transfer from UO2 in zinc phosphate glass

Enhancement of Sm³⁺ emission has been observed as a result of non-radiative energy transfer from optically excited UO₂⁺⁺ in zinc phosphate glass. The study is primarily done by observing the decrease in UO₂⁺⁺ emission with varying Sm³⁺ concentration. The energy transfer mechanism is found to be mainly electric dipole-dipole in nature. Transfer probabilities efficiencies and average donor-acceptor distances have been calculated.     

Enhanced Eu emission by non-radiative energy transfer from Tb in zinc phosphate glass

Energy transfer studies have been made in terbium-europium-doped zinc phosphate glass at room temperature. Enhancement of the Eu³⁺ (⁵D₀→⁷F manifold) emission and a decrease in the Tb³⁺ emission (⁵D₄→⁷F manifold) have been observed as a result of energy transfer from Tb³⁺ ions to europium ions. The energy transfer mechanisms have been found to be mainly electric dipole-dipole in nature. The energy transfer efficiencies, transfer probabilities and average donor-acceptor distances have been calculated.     

Biodegradation behavior of chitosan/calcium phosphate composites

A variety of biomimetic materials with structural and mechanical equivalence to bone have been developed to repair bone defects. Chitosan/calcium phosphate composites composed of bioactive calcium phosphate and flexible chitosan were made by a simple mixing-and-heating method. Mechanical properties, morphology, phase composition, and weight change after immersion in Hanks’ solution were evaluated. Experimental results showed that the formation of pores/cracks on immersed sample surface obviously depended on the calcium phosphate content and immersion time. The immersion time imposed in this study did have a statistically significant effect on mechanical properties. When immersed for 90 days in Hanks’ solution, the strength of immersed composites containing 10 wt/v% calcium phosphate with the initial strength of 27 MPa was about 2 MPa, having a reduction of 92%. Based on the above results, the organic–inorganic hybrid composites with high initial strength might be an acceptable material candidate for bone tissue repair.     

Electrical conductivity improvement of aeronautical carbon fiber reinforced polyepoxy composites by insertion of carbon nanotubes

An increase and homogenization of electrical conductivity is essential in epoxy carbon fiber laminar aeronautical composites. Dynamic conductivity measurements have shown a very poor transversal conductivity. Double wall carbon nanotubes have been introduced into the epoxy matrix to increase the electrical conductivity. The conductivity and the degree of dispersion of carbon nanotubes in epoxy matrix were evaluated. The epoxy matrix was filled with 0.4 wt.% of CNTs to establish the percolation threshold. A very low value of carbon nanotubes is crucial to maintain the mechanical properties and avoid an overload of the composite weight. The final carbon fiber aeronautical composite realized with the carbon nanotubes epoxy filled was studied. The conductivity measurements have shown a large increase of the transversal electrical conductivity. The percolative network has been established and scanning electron microscopy images confirm the presence of the carbon nanotube conductive pathway in the carbon fiber ply. The transversal bulk conductivity has been homogenized and improved to 10^? 1 S·m^? 1 for a carbon nanotubes loading near 0.12 wt.%.     

Surface conductivity of leached glass

In order to obtain unambiguous results, the surface conductivity measurements were carried out on intentionally leached specimens of a sodium-aluminium silicate glass. The surface conductivity of rod shaped samples was determined at 25°C at various humidities and was interpreted on the basis of the sodium ion distribution in the surface layer. The surface conductivity increases with humidity only in highly wet atmosphere; in the lower part of the humidity range, however, it is constant. The constant value has been attributed to an interior stratum which is clearly not exposed to the direct influence of the atmosphere. The excess of the surface conductivity above this level may be due to a moisture surface film, which vanishes in less humid atmosphere, or to a very thin gel layer. On specimens of glass electrode type, the contribution of the surface layer to the resistance of the electrode wall was determined and a highly resisting surface layer fraction was detected. Both high maximum and deep minimum in conductivity were established within the leached layer. The differences in (volume) conductivity between the subsequent strata are estimated to be in the range of orders of magnitude. Some hypotheses concerning the conduction mechanism are presented.     

Electrical conductivity of pyrolyzed polyacrylonitrile

Abstract

Using ultrapure samples of polyacrylonitrile (PAN) of 485,000 or 150,000 average molecular weight solution cast in dimethylformamide, the dc conductivity ([sgrave]) of pyrolyzed PAN (PANP) films has been studied for pyrolysis temperatures (T_p) of 280-435°C. Conductivity measurements made during pyrolysis indicate the onset of a dramatic increase in [sgrave] for T_p of 390-435°C. Conductivities as high as 5 (ohm-cm)^?1 have been observed for T_p < 435°C. This situation contrasts sharply with previous literature which had indicated that a increased uniformly and monotonically with T_p for 200°C < T_p < 900°C and that values of [sgrave] > 1 (ohm-cm)^?1 were observed only for T_p > 600°C. Our results indicate that the maximum value of [sgrave] obtained is not a strong function of T_p (390°C < T_p < 435°C) or of molecular weight. However, the rate of increase of [sgrave](t) is strongly dependent on T_p in this range. After pyrolysis, repeated heating and cooling below T_p do not alter [sgrave](T). IR spectra show that the sudden increase in [sgrave] is correlated to the formation of conjugated C=C and C=N bonds. The shape of [sgrave](T) suggests that conduction is probably due to hopping.     

Electrical characterization of SiO2:LiNbO3 glass and glass–ceramics using dc conductivity,TSDC measurements and dielectric spectroscopy

The aim of this research is the study of the structural, morphological and electrical properties of a 44SiO₂–33Li₂O–23Nb₂O₅ (mol%) glass and glass–ceramics. XRD, SEM, Raman and dielectric spectroscopy and (Thermally stimulated DC) TSDC measurements were used to characterize the samples. The LiNbO₃ crystalline phase was detected, by XRD and Raman spectroscopy, in the samples treated above 873 K. The volume ratio of the particles increases with increase in heat-treatment temperature. The behavior of the σ_dc and σ_ac, with the increase of the heat-treatment (HT) temperature, was related with the decrease of the free ions number in the glass matrix and consequent increase of the volume ratio between the LiNbO₃ crystalline phase and the glass matrix. The ε′ value decreases with the increase of the HT temperature. The complex impedance spectra were fitted to a equivalent electric circuit. The Z″ vs. Z′ plots of the samples HT below 873 K, indicate the existence of a distribution of relaxation times. The TSDC measurements revealed the presence of three depolarization peaks in the as-prepared and 550HT treated sample. The sample HT575 presents two TSDC peaks, and the samples HT600 and HT650 one TSDC peak. These peaks were correlated with the structure and mobility of ions in the prepared glass and glass–ceramics. The behavior of the dc and ac conductivities, TSDC peaks and dielectrical characteristics reflect the important role carried out by the treatment temperature in the formation of a glass ceramic structure.     

Formation of low density polyethylene/hollow glass microspheres composites

Hydrogen is used to absorb heavy particle radiation, which is the most damaging radiation in space for humans. Low density polyethylene/hollow glass microsphere composites have been suggested as a possible radiation shield because of the high concentration of hydrogen and the low gravimetric density of the microspheres. Composites pressed under 3.90 MPa (566 psi) and 120 °C have the highest probability of success thus far compared to polymers pressed at higher pressures and lower temperatures. Hollow glass microspheres made of borosilicate glasses do not break as easily as hollow glass microspheres made of aluminosilicate glasses. A smooth microsphere surface is better than a rough surface because it distributes the force more evenly, resulting in a more hydrostatic stress environment.     

Electrical properties of phosphate glasses

The electrical properties of glasses in the Na₂OP₂O₅, Ag₂OP₂O₅ and (1?x)Na₂OxAg₂OP₂O₅ systems have been measured over a range of temperature and composition.The properties of the Na₂OP₂O₅ and Ag₂OP₂O₅ glasses have been compared within the phosphate system as well as with silicate glasses. The silver-containing glasses show higher conductivity and lower temperature coefficients when compared with the sodium-containing glasses. A maximum in the room temperature resistivity of the (1?x)Na₂O?xAg₂O?P₂O₅ system was found around the mole ratio of 0.16:0.84 Ag₂O:Na₂O, indicating a mixed-alkali effect. A similar effect was seen in the tan δ, but not in the T_g-against-composition plots. A linear relationship was noted for the tan δ-versus-log₁₀ (resistivity) plot, as has been seen in other glass-forming systems.     

Fast ion conducting phosphate glasses and glass ceramic composites: Promising materials for solid state batteries

Fast ion conducting (FIC) phosphate glasses and glass ceramic composites have gained considerable importance due to their potential applications in the fabrication of solid-state batteries and other electrochemical devices. We, therefore, present an overview on various types of FIC glasses and glass ceramic composites. Silver phosphate glasses doped with different weight percent of lithium chloride (1, 5, 10 and 15 wt.%) were synthesized by melt quenching technique. The Ag₂O–P₂O₅–(15 wt.%) LiCl glass exhibited the maximum electrical conductivity (σ = 8.91 × 10^? 5 S cm^? 1 at room temperature and 4.16 × 10^? 3 S cm^? 1 at 200 °C). Using this glass as an amorphous host material, glass–ceramic composites of Ag₂O–P₂O₅–(15 wt.%) LiCl:xAl₂O₃ (x = 5–50 wt.%) were prepared. The ionic transference number, electrical conductivity, ionic mobility and carrier ion concentration of the synthesized samples were measured. Ag₂O–P₂O₅–(15 wt.%) LiCl:(25 wt.%) Al₂O₃ composite system exhibited the maximum σ value (σ = 3.32 × 10^? 4 S cm^? 1 at room temperature and 2.88 × 10^? 2 S cm^? 1 at 200 °C ). Solid‐state batteries using undoped Ag₂O–P₂O₅ glass, Ag₂O–P₂O₅–(15 wt.%) LiCl glass and glass ceramic composite containing 25 wt.% Al₂O₃ as electrolytes were fabricated. The open circuit voltage (OCV) values and discharge time of these cells were measured and compared. It is found that the glass ceramic composites show enhanced ionic conduction, better OCV value and discharge characteristics.     

Surface nitridation of a phosphate glass

Phosphate glass surfaces were nitrided by reacting them in dry ammonia at temperatures near the glass transition temperature (T_g) for up to 100 h. These treatments have significant effects on surface dependent glass properties. For example, the dissolution rate of a sodium-barium phosphate glass (T_g = 345°C) decreased by over an order of magnitude after 24 h in ammonia at T_g. X-ray photoelectron spectroscopic (XPS) analyses show that nitrogen in chemically incorporated into the glass structure at levels up to 3–5 at.%. Elemental depth profiles, obtained by XPS (for N) and by elastic recoil detection (ERD) analyses (for N and H), indicate that the surface oxynitrile layer extends to about 1 μm in depth. XPS analyses of in situ treated samples reveals the presence of several nitrogen species which affect the surface dependent properties by increasing the structural crosslink density of the glass surface.