Temperature and pressure dependence of direct current electrical resistivity in the Na2O-ZnO-B2O3 glass system

Two series of glasses were prepared, xNa2O, yZnO, 100 - x - yB2O3 and 30 - xNa2O, xZnO, 70B2O3 (mol%). The temperature dependence of the direct current resistivity was measured from room temperature to about 700 K and in both series of glasses we observed a simple Arrhenius type of temperature dependence. However, the resistivity of the binary alkali glass increased steeply by as much as two orders of magnitude with the addition of even a small quantity of ZnO and remained virtually unaffected by further addition of ZnO. The resistivity decreases gradually with increasing pressure in Na2O-B2O3 but increases with increasing pressure with the addition of ZnO.

Fabrication of Transparent BaNaB9O15 Glass-Microcrystal Composites

Transparent glasses in the BaO-Na2O-B2O3 (BNBO) system were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were confirmed by x-ray powder diffraction (XRD) and differential thermal analysis (DTA), respectively. Cyclic heat treatment of the as-quenched glasses yielded transparent glass-microcrystal composites. The volume fraction of the crystallites and their sizes could be easily controlled by this process. Heat-treated samples were highly transparent owing to the minimum mismatch between the refractive indices of the crystallites and the glass residual matrix. BNBO samples that were heat treated at 540A degrees C for 4 h for 10 cycles were found to be 60% to 70% transparent in the 500 nm to 900 nm wavelength range.

High-Resolution Magic Angle Spinning Nmr-Studies Of P-31 And B-11 In Fast Ion Conducting Agi-Ag2o-P2o5 And Agi-Ag2o-B2o3 Glasses

Silver iodide-based fast ion conducting glasses containing silver phosphate and silver borate have been studied. An attempt is made to identify the interaction between anions by studying the chemical shifts of31P and11B atoms in high resolution (HR) magic angle spinning (MAS) NMR spectra. Variation in the chemical shifts of31P or11B has been observed which is attributed to the change in the partial charge on the31P or11B. This is indicative of the change in the electronegativity of the anion matrix as a whole. This in turn is interpreted as due to significant interaction among anions. The significance of such interaction to the concept of structural unpinning of silver ions in fast ion conducting glasses is discussed.

Thermal properties of 3BaO-3TiO(2)-B2O3 glasses

Transparent glasses in the system 3BaO-3TiO2-B2O3 (BTBO) were fabricated via the conventional melt-quenching technique. The as-quenched samples were confirmed to be non-crystalline by differential thermal analysis (DTA). Thermal parameters were evaluated using non-isothermal DTA experiments. The Kauzmann temperature was found to be 759 K based on heating-rate-dependent glass transition and crystallization temperatures. A theoretical relation for the temperature-dependent viscosity is proposed for these glasses and glass-ceramics.

Possible mechanism of charge transport and dielectric relaxation in SrO-Bi2O3-B2O3 glasses

Transparent SrBi2B2O7 glasses were prepared via melt-quenching technique and characterized using differential scanning calorimetry and x-ray powder diffraction. The ac conductivities of the glasses were studied as a function of frequency (100 Hz-10 MHz) at different temperatures. The frequency dependence of conductivity has been analyzed using Almond-West expression. The exponent n was nearly unaffected by temperature. Impedance and modulus spectroscopies were employed to further examine the electrical data. Dielectric relaxation exhibited a stretched exponential behavior with a stretching exponent beta independent of temperature. From conductivity analysis we have proposed that the charge transport occurs through the participation of nonbridging oxygen (NBO), which switches positions in a facile manner. The stretched exponential behavior appears to be a direct consequence of the NBO switching mechanism of charge transport.

Low loss and frequency (1 kHz-1 MHz) independent dielectric characteristics of 3BaO-3TiO(2)-B2O3 glasses

X-ray powder diffraction along with differential thermal analysis carried out on the as-quenched samples in the 3BaO-3TiO(2)-B2O3 system confirmed their amorphous and glassy nature, respectively. The dielectric constants in the 1 kHz-1 MHz frequency range were measured as a function of temperature (323-748 K). The dielectric constant and loss were found to be frequency independent in the 323-473 K temperature range. The temperature coefficient of dielectric constant was estimated using Havinga's formula and found to be 16 ppm K-1. The electrical relaxation was rationalized using the electric modulus formalism. The dielectric constant and loss were 17 +/- 0.5 and 0.005 +/- 0.001, respectively at 323 K in the 1 kHz-1 MHz frequency range which may be of considerable interest to capacitor industry.

Effect of the addition of B2O3 and BaO-B2O3-SiO2 glasses on the microstructure and dielectric properties of giant dielectric constant material CaCu3Ti4O12

The effect of the addition of glassy phases on the microstructure and dielectric properties of CaCu3Ti4O12 (CCTO) ceramics was investigated. Both single-component (B2O3) and multi-cornponent (30wt% BaO-60wt% B2O3-10wt% SiO2 (BBS)) glass systems were chosen to study their effect on the density, microstructure and dielectric properties of CCTO. Addition of an optimum amount of B2O3 glass facilitated grain growth and an increase in dielectric constant. However, further increase in the B2O3 content resulted in its segregation at the grain boundaries associated with a reduction in the grain size. In contrast, BBS glass addition resulted in well-faceted grains and increase in the dielectric constant and decrease in the dielectric loss. An internal barrier layer capacitance (IBLC) model was invoked to correlate the dielectric constant with the grain size in these samples. (c) 2007 Elsevier Inc. All rights reserved.

Phosphorus Partition between Liquid Steel and CaO-SiO2-P2O5-MgO Slag Containing Low FeO

CaO-SiO2-FeOx-P2O5-MgO bearing slags are typical in the basic oxygen steelmaking (BOS) process. The partition ratio of phosphorus between slag and steel is an index of the phosphorus holding capacity of the slag, which determines the phosphorus content achievable in the finished steel. The influences of FeO concentration and basicity on the equilibrium phosphorus partition ratios were experimentally determined at temperatures of 1873 and 1923 K, for conditions of MgO saturation. The partition ratio initially increased with basicity but attained a constant value beyond basicity of 2.5. An increase in FeO concentration up to approximately 13 to 14 mass pet was beneficial for phosphorus partition.

A chemical approach to an understanding of the fast ion conduction in silver iodide-silver oxysalt glasses

A number of AgI based fast ion conducting glasses, with a general formula AgI---Ag2O---MxOy (MxOy=MoO3, SeO3, WO3, V2O5, P2O5, GeO2, B2O3, As2O3, CrO3) have been studied. A chemical approach is made to investigate the origin of fast ion conduction in these glasses. An index known as Image tructural Image npinning Image umber, SUN (S), has been defined for the purpose, based on the unscreened nuclear charge of silver ions and the equilibrium lectronegativities of the halide-oxyanion matrix in these glasses. The variation of the glass transition temperature, Tg, conductivity, σ, and the energy of activation, Ea, with the concentration of AgI are discussed in the light of the structural unpinning number. Conductivities increase uniformly in any given glass series as a smooth function of S and level off at very high values. The entire range of conductivity appears to vary as ln Image , where ln σ0 corresponds roughly to the conductivity of the hypothetical AgI glass and “a” is a constant which could be obtained as the slope in the graph of ln Ea versus S. It is suggested that the increase in the concentration of AgI beyond 75–80 mole% in the glass is not advantageous from the conductivity point of view.

properties of Na2O in Nasicon solid solution, Na1+xZr2SixP3-xO12

The thermodynamic activity of sodium oxide (Na2O) in the Nasicon solid solution series, Na1+xZr2SixO12, has been measured in the temperature range 700–1100 K using solid state galvanic cells: Pt|CO2 + O2|Na2CO3?Na1+xZr2SixP3-xO12?(Y2O3)ZrO2?In + In2O3|Ta, Pt for 1 = ? = 2.5, and Pt?CO2 + O2?Na2CO3?ß-alumina?Na1+xZr2SixP3-xO12?Ar + O2?Pt for x = 0, 0.5, 2.5, and 3. The former cell, where the Nasicon solid solution is used as an electrolyte along with yttria-stabilized zirconia, is well suited for Nasicon compositions with high ionic conductivity. In the latter cell, ß-alumina is used as an electrolyte and the Nasicon solid solution forms an electrode. The chemical potential of Na2O is found to increase monotonically with x at constant temperature. The partial entropy of Na2O decreases continuously with x. However, the partial enthalpy exhibits a maximum at x = 2. This suggests that the binding energy is minimum at the composition where ionic conductivity and cell volume have maximum values.

Thermodynamic partial properties of Na2O in Nasicon solid solution, Na1+xZr2SixP3-xO12

The thermodynamic activity of sodium oxide (Na2O) in the Nasicon solid solution series, Na1+xZr2SixO12, has been measured in the temperature range 700�1100 K using solid state galvanic cells: Pt|CO2 + O2|Na2CO3?Na1+xZr2SixP3-xO12?(Y2O3)ZrO2?In + In2O3|Ta, Pt for 1 = ? = 2.5, and Pt?CO2 + O2?Na2CO3?ß-alumina?Na1+xZr2SixP3-xO12?Ar + O2?Pt for x = 0, 0.5, 2.5, and 3. The former cell, where the Nasicon solid solution is used as an electrolyte along with yttria-stabilized zirconia, is well suited for Nasicon compositions with high ionic conductivity. In the latter cell, ß-alumina is used as an electrolyte and the Nasicon solid solution forms an electrode. The chemical potential of Na2O is found to increase monotonically with x at constant temperature. The partial entropy of Na2O decreases continuously with x. However, the partial enthalpy exhibits a maximum at x = 2. This suggests that the binding energy is minimum at the composition where ionic conductivity and cell volume have maximum values.

Potentiometric determination of activities in the two-phase fields of the system Na2O---(α)Al2O3

Three compounds have been found to be stable in the pseudobinary system Na2O---(α)Al2O3 between 825 and 1400 K; two nonstoichiometric phases, β-alumina and β″-alumina, and NaAlO2. The homogeneity of β-alumina ranges from 9.5 to 11 mol% Na2O, while that of β″-alumina from 13.3 to 15.9 mol% Na2O at 1173 K. The activity of Na2O in the two-phase fields has been determined by a solid-state potentiometric technique. Since both β- and β″-alumina are fast sodium ion conductors, biphasic solid electrolyte tubes were used in these electrochemical measurements. The open circuit emf of the following cells were measured from 790 to 980 K: [GRAPHICS] The partial molar Gibbs' energy of Na2O relative to gamma-Na2O in the two-phase regions can be represented as: DELTA-GBAR(Na2O)(alpha- + beta-alumina) = -270,900 + 24.03 T, DELTA-GBAR(Na2O)(beta- + beta"-alumina) = -232,700 + 56.19 T, and DELTA-GBAR(Na2O)(beta"-alumina + NaAlO2) = -13,100 - 4.51 T J mol-1. Similar galvanic cells using a Au-Na alloy and a mixture of Co + CoAl(2+2x)O4+3x + (alpha)Al2O3 as electrodes were used at 1400 K. Thermodynamic data obtained in these studies are used to evaluate phase relations and partial pressure of sodium in the Na2O-(alpha) Al2O3 system as a function of oxygen partial pressure, composition and temperature.

Mössbauer effect and electron paramagnetic resonance studies on zinc borate glasses containing transition metal oxides

Studies have been carried out in glasses containing Fe2O3, V2O5, and Fe2O3 + V2O5. Mossbauer studies in the ZnO-B2O3-Fe2O3 system show that iron is present as Fe3+ with tetrahedral coordination and that the isomer shift and the quadrupole splitting decrease with increase of Fe2O3 Content; similarly, the isomer shift and quadrupole splitting are also found to decrease with increasing ZnO. On the other hand, in the Na2O-ZnO-B2O3-Fe2O3 system, the isomer shift increases with Na2O or ZnO while the quadrupole splitting is fairly insensitive. Electron paramagnetic resonance in the ZnO-B2O3-Fe2O3 system shows signals at g = 4.20 and 2.0, whose intensity and linewidth show strong dependence on Fe2O3 content. In the ZnO-B2O3-V2O5 system, electron paramagnetic resonance shows that vanadium is present as the vanadyl complex, and the hyperfine coupling constants, A(parallel-to) and A(perpendicular-to) decrease with increasing V2O5 content; on the other hand, g(parallel-to) decreases and g(perpendicular-to) increases slightly, indicating an increase in tetragonal distortion. Zinc borate glasses containing Fe2O3 + V2O5 do not show the hyperfine structure of V4+ due to the interaction between Fe3+ and V4+

Lithium ion transport in Li2SO4-Li2O-B2O3 glasses

Electrical conductivity and dielectric relaxation studies with a wide range of compositions of lithium ion conducting glasses belonging to the ternary glass system Li2SO4-Li2O-B2-O3- have been carried out over the temperature range 150-450 K and between 10 - 10(7) Hz. DC conductivities exhibit two different activation regions. This seems to suggest the presence of a cluster tissue texture in these glasses with weakly ordered clusters of Li2SO4 and lithium berates being held together by a truly amorphous tissue of the same average composition as clusters. AC conductivity behaviour of these glasses has been analysed using both power law and stretched exponential relaxation functions. The variation of the power law exponent s and the stretched exponent beta with temperature seems to be consistent with the presence of a cluster tissue texture in these glasses.