Electrical Conductivity of PbO-P2O5-V2O5Glasses

The dc conductivities (α) of PbO-P₂O₅-V₂O₅ glasses containing up to 80 mol% V₂O₅ were measured at T = 100°C to T = 10°C below the glass transition temperature. Dielectric constants at 1 MHz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism of glasses containing >10 mol% V₂O₅ was considered to be small-polaron hopping, as previously reported for other vanadate glasses. The temperature dependence of α was exponential, with α= (αo/ T ) exp(− W/kT ). When the V₂O₅ content was ≥50 mol%, W decreased and α increased with increasing V₂O₅ content, and the adiabatic approximation could be applied. In the composition range between 10 and 50 mol% V₂O₅, α increased with increasing V₂O₅ content, but W varied little. In this region, the hopping conduction was characterized as nonadiabatic. The effect of dielectric constants and V ion spacing on W is discussed.     

Effects of V and Mn Colorants on the Crystallization Behavior and Optical Properties of Ce-Doped Li-Disilicate Glass–Ceramics

The critical cooling rate and fluorescence properties of lithium (Li) disilicate glasses and glass–ceramics, doped with 2.0 wt% CeO₂ and with up to 0.7 wt% V₂O₅ and 0.3 wt% MnO₂ added as colorants, were investigated. The critical cooling rates, R _c, of glass melts were determined using differential thermal analysis and were found to be dependent on the relative concentrations of V₂O₅ and MnO₂, decreasing from 25±3° to 16±3°C/min. Annealed glasses were heat treated first to 670°C, and then to 850°C to form Li metasilicate and Li disilicate glass–ceramics, respectively. The fluorescence intensities of the Ce-doped glasses and glass–ceramics decrease by a factor of 100 with the addition of the transition metal oxides. This optical quenching effect is explained by the association of the Ce³⁺ ions with the transition metal ions in the residual glassy phase of the glass–ceramics.     

Effect of V2O5 Doping on the Sintering and Dielectric Properties of M-Phase Li1+x−yNb1−x−3yTix+4yO3 Ceramics

The effect of the addition of V₂O₅ on the structure, sintering and dielectric properties of M -phase (Li_{1+ x − y} Nb_{1− x −3 y} Ti _x +4 _y )O₃ ceramics has been investigated. Homogeneous substitution of V⁵⁺ for Nb⁵⁺ was obtained in LiNb_{0.6(1− x )}V_{0.6 x} Ti_0.5O₃ for x ≤ 0.02. The addition of V₂O₅ led to a large reduction in the sintering temperature and samples with x = 0.02 could be fully densified at 900°C. The substitution of vanadia had a relatively minor adverse effect on the microwave dielectric properties of the M -phase system and the x = 0.02 ceramics had [alt epsilon]_r= 66, Q × f = 3800 at 5.6 GHz, and τ_f= 11 ppm/°C. Preliminary investigations suggest that silver metallization does not diffuse into the V₂O₅-doped M -phase ceramics at 900°C, making these materials potential candidates for low-temperature cofired ceramic (LTCC) applications.     

Electrical Conductivity of TiO2-V2O5-P205 Glasses

The dc conductivities (σ) of V₂O₅-P₂O₅ glasses containing up to 30 mol% TiO₂ were measured at T=100° to ∼10°C below the glass-transition temperature. Dielectric constants from 30 to 10⁶ Hz, densities, and the fraction of reduced V ion were measured at room temperature. The conduction mechanism was considered to be small polaron hopping between V ions, as previously reported for V₂O₅-P₂O₅ glass. The temperature dependence of σ was exponential with σ = σ₀ exp(-W/kT ) in the high-temperature range. When part of the P₂O₅ was replaced by TiO_2,σ increased and W decreased. The hopping energy depended on the reciprocal dielectric constant which, in this case, increased with increasing TiO₂ content.     

Influence of V2O5 Additions to 5Li2O–1Nb2O5–5TiO2 Ceramics on Sintering Temperature and Microwave Dielectric Properties

The effects of the addition of V₂O₅ on the sintering behavior, microstructure, and microwave dielectric properties of 5Li₂O–1Nb₂O₅–5TiO₂ (LNT) ceramics have been investigated. With low-level doping of V₂O₅ (≤3 wt%), the microstructure of the LNT ceramic changed from a special two-level intergrowth structure into a two-phase composite structure with separate grains. And the sintering temperature of the LNT ceramics could be lowered to around 900°C by adding a small amount of V₂O₅ without much degradation in microwave dielectric properties. Typically, better microwave dielectric properties of ɛ_r=41.7, Q × f =7820 GHz, and τ _f =45 ppm/°C could be obtained for the 1 wt% V₂O₅-doped ceramics sintered at 900°C.     

Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses

The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 mol% V₂O₅ were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V⁴⁺ ions in the glassy matrix exists, and a transition temperature near - 70°C was observed. As-cast glasses with high V₂O₅ concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium-rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions at +70° and -120°C, the Neel temperatures of VO₂ and V₂O₃, respectively.     

Microwave Dielectric Properties of 5Li2O–0.583Nb2O5–3.248TiO2 Ceramics with V2O5

The effects of V₂O₅ addition on the sintering behavior, microstructure, and the microwave dielectric properties of 5Li₂O–0.583Nb₂O₅–3.248TiO₂ (LNT) ceramics have been investigated. With addition of low-level doping of V₂O₅ (≤2 wt%), the sintering temperature of the LNT ceramics could be lowered down to around 920°C due to the liquid phase effect. A secondary phase was observed at the level of 2 wt% V₂O₅ addition. The addition of V₂O₅ does not induce much degradation in the microwave dielectric properties but lowers the τ_f value to near zero. Typically, the excellent microwave dielectric properties of ɛ_r=21.5, Q × f =32 938 GHz, and τ_f=6.1 ppm/°C could be obtained for the 1 wt% V₂O₅-doped sample sintered at 920°C, which is promising for application of the multilayer microwave devices using Ag as an internal electrode.     

Electronic Conductivity and Related Properties of Amorphous and Crystallized V2O5-Based Glasses

Crystallization of V₂O₃ from V₂O₃P₂O₃, glasses containing 0 to 9 mol% B₂O₃, during heat treatment in the range 220° to 410°C, caused progressive micro structural changes which dramatically affected the electronic conductivity (γ), the activation energy for conduction ( W ), and the resistance to chemical attack. All compositions were ≊83% crystalline after heating to 410°C. As a result, the values of γ and W were almost identical to those observed for pure polycrystalline V₂O₅.     

Synthesis of V2O3 Powder by Evaporative Decomposition of Solutions and H2 Reduction

The evaporative decomposition of solutions method was used to form V₂O₅. Spraying above the congruent melting temperature of V₂O₅ (690°C) resulted in dense spherical particles with a smooth surface. Spraying below the V₂O₅ melting temperature yielded porous V₂O₅ powder with a rough surface. Reduction of the V₂O₅ to V₂O₃ was done in a H₂ atmosphere. Spherical V₂O₃ powder was attained when the reduction temperature was low enough to reduce the V₂O₅ surface before partial sintering (necking) between V₂O₅ particles occurred. The resulting V₂O₃ particle size was smaller than the precursor V₂O₅ powder as expected by the differences in densities between V₂O₅ ( p = 3.36 g/cm³) and V₂O₃ ( p = 4.87 g/cm³).     

Preliminary Observations on Phase Relations in the "V2O3–FeO" and V2O3–TiO2 Systems from 1400°C to 1600°C in Reducing Atmospheres

Phase relations within the "V₂O₃–FeO" and V₂O₃–TiO₂ oxide systems were determined using the quench technique. Experimental conditions were as follows: partial oxygen pressures of 3.02 × 10⁻¹⁰, 2.99 × 10⁻⁹, and 2.31 × 10⁻⁸ atm at 1400°, 1500°, and 1600°C, respectively. Analysis techniques that were used to determine the phase relations within the reacted samples included X-ray diffractometry, electron probe microanalysis (energy-dispersive spectroscopy and wavelength-dispersive spectroscopy), and optical microscopy. The solid-solution phases M₂O₃, M₃O₅, and higher Magneli phases (M _n O_{2 n −1}, where M = V, Ti) were identified in the V₂O₃–TiO₂ system. In the "V₂O₃–FeO" system, the solid-solution phases M₂O₃ and M₃O₄ (where M = V, Ti), as well as liquid, were identified.     

Formation of Frozen α-Agl in Twin-Roller-Quenched Agl─Ag2 O─MxOy (MxOy= WO3, V2O5) Glasses at Ambient Temperature

Superionic conductor α-AgI, which is stable only above 147°C, was successfully frozen at ambient temperature in AgI─Ag₂O─M_xO_y (M_xO_y= WO₃, V₂O₅) glass matrices by a twin-roller-quenching technique. The system with WO₃, provided the larger composition regions where α-AgI was frozen at ambient temperature, compared to the system with V₂O₅. The matrix glasses with higher glass-transition temperatures had a stronger effect in depressing the α–β transformation of AgI. The α-AgI-frozen samples exhibited extremely large conductivities of 3 × 10⁻²-5 × 10⁻²S.cm⁻¹at 25°C.     

Preparation of Alkoxy-Derived Tantalum Vanadate

Compound formation in the system Ta₂O₅–V₂O₅ has been studied using amorphous materials prepared by the simultaneous hydrolysis of tantalum and vanadyl alkoxides. Three compounds exist in this system: 9Ta₂O₅· V₂O₅, 9Ta₂O₅·2V₂O₅, and Ta₂O₅·V₂O₅ (TaVO₅). Solid solutions of δ-Ta₂O₅ are formed at low temperatures up to 10 mol% V₂O₅. They transform to β-Ta₂O₅ solid solutions at higher temperatures; the transformation temperature falls with increasing V₂O₅ A new compound, 9Ta₂O₅·V₂O₅, 670° to 755°. It has an orthorhombic unit cell with a = 0.7859 nm, b = 1.733 nm, and c = 1.766 nm. Orthorhombic TaVO₅ crystallized at 535° to 560° decomposes into 9Ta₂O₅°V₂O₅ at 1010°.     

Infrared Spectra of GeO2-P4O10-V2O5 Glasses and Their Relation to Structure and Electronic Conduction

Infrared spectra of binary and ternary compositions in the glassy state and in the devitrified crystalline state in the system GeO₂-P₄O₁₀-V₂O₅ were studied and compared with infrared spectra of crystalline spinels, which are known to contain V⁵⁺ ions in sixfold coordination. Results indicated that the fundamental vibration frequency of the V—O bond occurred at wave number 1015 cm⁻¹. The spectra also provided evidence that the V⁵⁺ ion existed in sixfold coordination in the glassy state, as well as in the devitrified crystalline state, and that the VO₆ octahedron retained its identity even at low concentrations and melting temperatures of 1450°C. Conductivity measurements indicated that, as the concentration of V₂O₅ decreased below the critical range of 5 to 10 mole %, there was an abrupt loss in the electronic conductivity of the glasses; the conductivity decreased with increasing concentration of the lower valence states of vanadium. A mechanism of conduction compatible with the structure of glasses in the system is suggested to explain these observations.     

Phase Equilibria in the System SrO-CdO-V2O5

Phase equilibria in the system SrO-CdO-V₂O₅ in air were established from data obtained by DTA, quenching, and high-temperature solid-state reaction experiments. The SrO-V₂O₅ boundary system contains 4 compounds at SrO to V₂O₅ molar ratios of 4:1, 3:1, 2:1, and 1:1. A fifth compound with a molar composition of ∼10:3 with the apatite crystal structure was also found; it may, however, be a hydroxyapatite phase. The CdO-V₂O₅ system contains the compounds 3CdO·V₂O₅, 2CdO·V₂O₅, and CdO·V₂O₅. The latter compound exhibits a rapid reversible polymorphic transition at 180°C. Complete solid solubility exists in the SrO-CdO system. The most probable compatibility relations were determined from the data available for the SrO-CdO-V₂O₅ ternary system. Limited solid solubility exists between SrO·V₂O₅ and CdO·V₂O₅, and the high-temperature CdO·V₂O₅ polymorph is stabilized to room temperature by solid solution of SrO·V₂O₅. Evidence for the existence of 2 ternary compounds with limited local solid solubility is also presented.     

Effect of Glass Additions on BaO–TiO2–WO3 Microwave Ceramics

The effect of glass addition on the properties of BaO–TiO₂-WO₃ microwave dielectric material N-35, which has Q = 5900 and K = 35 at 7.2 GHz for samples sintered at 1360°C, was investigated. Several glasses including B₂O₃, SiO₂, 5ZnO–2B₂O₃, and nine other commercial glasses were selected for this study. Among these glasses, one with a 5 wt% addition of B₂O₃ to N-35, when sintered at 1200°C, had the best dielectric properties: Q = 8300 and K = 34 at 8.5 GHz. Both Q and K increased with firing temperature as well as with density. The Q of N-35, when sintered with a ZnO–B₂O₃ glass system, showed a sudden drop in the sintering temperature to about 1000°C. The results of XRD, thermal analysis, and scanning electron microscopy indicated that the chemical reaction between the dielectric ceramics and glass had a greater effect on Q than on the density. The effects of the glass content and the mixing process on the densification and microwave dielectric properties are also presented. Ball milling improved the densification and dielectric properties of the N-35 sintered with ZnO–B₂O₃.     

Some Properties of the Oxides of Vanadium and Their Compounds

Vanadium tetroxide and vanadium pentoxide were prepared and some of their physical properties were measured. A brief survey was then made of some of their binary oxide compounds. Various mixtures of V₂O₄ or V₂O₆ and BeO, MgO, CaO, SrO, BaO, Al₂O₃, SiO₂, TiO₂, CeO₂, ZrO₂, Nb₂O₆, and U₃O₈ were heated. When compounds were formed, some of their properties were determined. Refractoriness, thermal expansion, and optical properties were considered of special interest. Vanadium pentoxide was found to have a linear thermal expansion of only 0.63 × 10⁻⁶ per °C. from 30° to 450°C.     

EPR of Vanadium(IV) in Lead Silicate Glass

EPR spectra of lead silicate glasses doped with small amounts of V₂O₅ were studied at −150°C to room temperature. Only the glasses with the higher SiO₂ contents produced EPR signals. The spin Hamiltonian parameters are characteristic of the V(IV) species in axial symmetry. The values of g, g ⊥, A, and B indicate that V(IV) is present as VO^2plus; in a tetragonally distorted octahedral site. This ion probably does not enter the SiO₂ network but rather behaves as a modifier cation.     

Humidity-Sensitive Characteristics of Porous La-Ti-V-O Glass-Ceramics

The humidity-sensitive characteristics of La₂O₃–TiO₂–V₂O₅ glass-ceramics were investigated as a function of additive amount of V₂O₅ to the precursor glass and the heating temperature of the glass to iduce phase separation. The microstructure of each glass-ceramic was strongly dependent upon the heating temperature. The specific impedance was lowered by increasing the amount of V₂O₅ additive. Among the elements studied, the LTV 2–2 element, which was prepared from as-cast glass, consisted of Na₂O:B₂O₃:La₂O₃: TiO₂: V₂O₅= 8.3:32.9:7.2:31.6:20.0 (molar ratio) after heating at 450°C for 12 h and subsequent leaching at 85°C for 24 h, and was found to be the most suitable material from the standpoint of humidity sensitivity, measurability, and response time.     

Eletrical Properties of Glasses in the System PbO-Al2O3-B2O3-SiO2

Glasses in the system Pb0–Al₂O₃-B₂O₃-SiO₂ are chemically stable over a wide composition range and have very desirable electrical characteristics such as high electrical resistivities and activation energies for conduction. Variations in these electrical properties were studied as a function of composition changes within the system, the object being to identify the role of the constituent oxides in achieving the highest activation energy and resistivity values consistent with moderate preparation temperatures. Measurements were made in the temperature range 25° to 400°C on carefully prepared glass disks in which the individual oxide components or different oxide ratios such as PbO/SiO₂, Al₂O₃/SiO₂, and B_sO₃/SiO₁ were systematically varied. The activation energy and resistivity values obtained ranged from 1.2 to 1.6 ev and 10° to 10¹⁴ ohm-cm, with dielectric constants ranging from 9 to 19 and densities from 4.30 to 4.50 g/cmY. Indications were that, for the composition range studied, the behavior manifested was basically that of the binary PbO-SO₂ glass with additions of Al₂O₃ or B₂O₃, even in small concentrations, sharply increasing the activation energy for conduction while lowering the density.     

Properties of Sm2O3─Al2O3─SiO2 Glasses for In Vivo Applications

The compositional range for glass formation below 1600°C in the Sm₂O₃─Al₂O₃─SiO₂ system is (9–25)Sm₂O₃─(10–35)Al₂O₃─(40–75)SiO₂ (mol%). Selected properties of the Sm₂O₃─Al₂O₃─SiO₂ (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm₂O₃ content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm₂O₃ content and with increasing temperature to 70°C. The transformation temperature ( T _g ) and dilatometric softening temperature ( T _d ) of the SmAS glasses exceeded 800° and 850°C, respectively.