EPR study of V2O5–P2O5–Li2O glass system

glass system, with 0 < x 50 mol%, was prepared and investigated by EPR method. For low content of V₂O₅ all the spectra present a hyperfine structure typical for isolated V⁴⁺ ions. With the increasing of V₂O₅ content, the EPR absorption signal showing hyperfine structure is superposed by a broad line without hyperfine structure characteristic for clustered ions. At high V₂O₅ content, the vanadium hyperfine structure disappears and only the broad line can be observed in the spectra. Spin Hamiltonian parameters g , g , A , A , dipolar hyperfine coupling parameters, P, and Fermi contact interaction parameters, K, have been calculated.The composition dependence of line widths of the first two absorptions from the parallel band and of the broad line characteristic to the cluster formations was also discussed.     

Characterization of SiO2–Na2O–Fe2O 3–CaO–P2O 5–B 2O 3 glass ceramics

Bioactivity and magnetic properties were investigated in glass and glass ceramics based on the SiO₂–Na₂O–Fe₂O₃–CaO–P₂O₅–B₂O₃ system to find their suitability as thermoseed for hyperthermia treatment of cancer. The effect of change in compositions on bioactivity was examined in simulated body fluids. The glass ceramic samples exhibit Na₃CaSi₃O₈ and Na_3-XFe_XPO₄ phases. After dipping the glass ceramic samples in simulated body fluids silica hydrogel first forms, followed by an amorphous calcium phosphate layer. Magnetic and microwave resonance experiments further demonstrate the potential of these glass ceramics for possible use in hyperthermia.     

Microwave dielectric properties of 3Li2O–Nb2O5–3TiO2 ceramics with Li2O–V2O5 additions

A new Li₂O–Nb₂O₅–TiO₂ (LNT) ceramic with the Li₂O:Nb₂O₅:TiO₂ mole ratio of 3:1:3 has been investigated. The compound is composed of two phases, the Li₂TiO₃ and “M-phase” solid solution phase. The microwave dielectric ceramic has low sintering temperature (∼1100 °C) and good microwave dielectric properties of a relatively high permittivity (∼51), high Q × f value up to 8700, and small temperature coefficient (∼37 ppm/°C). The low-amount doping of 0.83Li₂O–0.17V₂O₅ (LV) can effectively lower the sintering temperature from 1100 to 900 °C and induce no obvious degradation of the microwave dielectric properties. Typically, the 1 wt.% LV-doped ceramic sintered at 900 °C has better microwave dielectric properties of ε_r = 51.3, Q × f = 7235 GHz, τ _f  = 22 ppm/°C, which suggests that the ceramics can be applied in microwave LTCC devices.     

Microwave dielectric properties of CaO–La2O3–Nb2O5–TiO2 ceramics

A series of ceramics with a general formula Ca_1+xLa_4?xNb_xTi_5?xO₁₇ (0 ≤ x ≤ 4) were fabricated using the solid-state ceramic route. The phase, microstructure, and microwave dielectric properties varied distinctly with composition or the value of x. X-ray diffraction results showed that the two end member phases, CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇, crystallized into single phases with orthorhombic and monoclinic crystal structure, respectively. For intermediate compounds with x = 1, 2, and 3, mixture phases CaLa₄Ti₅O₁₇ and Ca₅Nb₄TiO₁₇ coexisted and a trace amount of second phase was detected. The ceramics showed high ε _r in the range of 45–52, relatively high quality factors with Q × f in the range of 9,870–15,680 GHz and τ _f value in the range between ?38 and ?126.4 ppm/°C. τ _f of CaLa₄Ti₅O₁₇ can be tuned to a near-zero value by addition of suitable amount of TiO₂.     

Effects of CaO/P2O5 ratio on the structure and elastic properties of SiO2–CaO–Na2O–P2O5 bioglasses

The evolution of elastic properties and structure upon the change of CaO/P₂O₅ ratio in SiO₂–CaO–Na₂O–P₂O₅ glasses (45S5-derived and 55S4-derived) at ambient conditions has been studied by using both Brillouin and Raman spectroscopy coupled with X-ray diffraction. Under the same SiO₂/Na₂O ratio, it is found that a decrease in CaO/P₂O₅ molar ratio has caused a more-polymerized silicate network via a net consumption of Q⁰, Q¹, and Q² species yet enriching in Q³ and Q⁴ species. Brillouin experiments revealed that all the bulk, shear and Young’s moduli of the glasses studied increases with the increase of CaO/P₂O₅ molar ratio. The unexpected variation trend in shear modulus can be correlated to the contribution from cohesion, the less-polymerized phosphate Q species, and density. Compared to the 45S5-derived, the more-polymerized 55S4-deived glass has a lower bulk but slightly higher shear modulus at the given CaO/P₂O₅ ratio.     

Effect of borosilicate glasses on the microwave dielectric properties of ZnO–Nb2O5–Ta2O5 system

(1 ? y)[0.5ZnNb₂O₆–0.5Zn₃Nb₂O₈]–yZnTa₂O₆ with y = 0.91 (ZNT) ceramic have been prepared by conventional solid state ceramic route. The effect of glass additives on the microstructure, densification, and microwave dielectric properties of the ZNT ceramic for low temperature co-fired ceramic applications was investigated. Different weight percentages of quenched glass such as ZnO–B₂O₃–SiO₂, BaO–B₂O₃–SiO₂, LiO–B₂O₃–SiO₂ and MgO–B₂O₃–SiO₂ were added to ZNT powder. The crystal structure of the ceramic–glass composites was studied by X-ray diffraction and microstructure by scanning electron microscopy. The microwave dielectric properties such as relative permittivity (ε_r), quality factor (Q_uxf) and co-efficient of temperature variation of resonant frequency (τ_f) of the ceramics have been measured in the frequency range 4–6 GHz. The 5 wt% ZnO–B₂O₃–SiO₂ added ZNT ceramic sintered at 900 °C showed: ε_r = 28.1, Q_uxf = 32820 GHz (at 4.92 GHz), and τ_f = ?7.7 ppm/^oC respectively.     

Phase Relations in the Na2O–Al2O3–Nb2O5and CaO–Al2O3–Nb2O5Systems

Phase relations in the Na₂O–Al₂O₃–Nb₂O₅and CaO–Al₂O₃–Nb₂O₅systems were studied. The Na₂O system was found to contain neither ternary compounds nor niobate–aluminate solid solutions. In the CaO system, a ternary compound of composition 4CaO · Al₂O₃·Nb₂O₅was identified (cubic structure, a= 7.628 Å, Z= 2, _meas= _x= 4.43 g/cm³).     

Effect of thermal treatment on elastic properties of SiO2–Na2O–CaO–P2O5 glasses for biomedical applications

Glasses of the system SiO₂–Na₂O–CaO–P₂O₅ have been prepared for different compositions of SiO₂ employing the normal melting and annealing technique. The glasses of different compositions have been subjected to different thermal treatments to explore the change in structure, mechanical and other related properties. The ultrasonic velocities and attenuation measurements have been made on different compositions of the pure and thermal-treated glasses at a fundamental frequency of 5 MHz at 303 K. The observed linear increase in density, velocities and elastic moduli with increase in thermal treatment temperature is same in all composition studied. The above results reveal an increase in hardness and the predominant nature of network bonds per unit volume rather than the coordination/cross-link changes, with the influence of thermal treatment.     

Influence of Nb2O5 on the varistor behavior of TiO2–Cr2O3 system

This work investigated the influence of Nb₂O₅ dopant on the varistor behavior of the ternary system (99.95 ? x)%TiO₂, 0.05 %Cr₂O₃, x%Nb₂O₅, where x = 0.10; 0.15; 0.20; 0.25 % in mol. The processing was carried out using the conventional oxide mixture method. The initial oxides were homogenized in alcoholic media in a ball mill, for 3 h, dried in oven and isostatically pressed at 210 MPa and sintered at 1,400 °C for 2 h in air atmosphere and cooled at 5 °C/min cooling rate, resulting in pellets with high densification. Electrical measurements in continuous current at different temperatures revealed that for the lowest Nb₂O₅ concentration the breakdown electric field, E_B = 4.41 V/cm and non-linear coefficient, α = 4.6 were obtained, and for the highest Nb₂O₅ concentration the breakdown electric field, E_B = 9.71 V/cm and non-linear coefficient, α = 15.3 were obtained. These low values in the breakdown electric field enable these varistor systems to be used in protection systems for low-voltage energy grids. Changes in the potential barrier present in the grain–grain boundaries could also be observed, in which the height increased and the width decreased with the increase in the dopant concentration. However, for x = 0.25 % in mol Nb₂O₅, a significant reduction in the potential barrier height and the voltage per barrier was obtained. Furthermore, the tendency to increase the volume of the unitary cell with the increase of dopant concentration, which was interrupted in the system with 0.25 % Nb₂O₅, was another evidence that suggested the occurrence of Nb₂O₅ segregation in the grain boundaries, or even that the reduction in the average grain size could possibly dilute Nb₂O₅ concentration in the grain boundaries. The average grain size was calculated through SEM micrographs and ranged from 7 to 16 μm, with larger sizes occurring for lower dopant concentrations and presenting higher porosity and lower uniformity in the grains shape.     

Photoluminescence and scintillation properties of Eu2O3–BaO–Nb2O5–TeO2 glass and glass ceramics

Journal of Materials Science: Materials in Electronics - 1Eu2O3–3BaO–20Nb2O5–76TeO2 glass and the corresponding glass-ceramics were synthesized with the aim to investigate the...     

Ti K-edge XANES study of the local environment of titanium in bioresorbable TiO2–CaO–Na2O–P2O5 glasses

Ti K-edge XANES (X-ray absorption near edge structure) spectroscopy has been used to study the local coordination of titanium in biocompatible and bioresorbable TiO₂–CaO–Na₂O–P₂O₅ glasses. Both conventional melt-quenched glasses of composition (TiO₂) _x (CaO)_0.30(Na₂O)_(0.20−x)(P₂O₅)_0.50, where x = 0.01, 0.03 and 0.05, and sol–gel derived (TiO₂)_0.25(CaO)_0.25(P₂O₅)_0.50 glass have been studied. The results show that in all the materials studied, titanium is surrounded by an octahedron of oxygen atoms. Further analysis reveals that the TiO₆ site in the amorphous samples is not heavily distorted relative to that in rutile, anatase or CaSiTiO₅. The spectra from the (TiO₂)_0.25(CaO)_0.25(P₂O₅)_0.50 sol–gel samples reveal greater distortion in the TiO₆ site in the dried gel compared to the heat-treated sol–gel glass. The XANES spectra from melt-quenched glass samples soaked in distilled water for various times do not shown any evidence of degradation of the titanium site over periods of up to 14 days.     

D.c. conductivity of V2O5–MnO–TeO2 glasses

Semiconductive oxide glasses in the system V2O5–MnO–TeO2 were prepared, and the mechanism of d.c. conduction was studied. The Seebeck coefficient measurements at temperatures from 375–475 K indicated the glasses to be n-type semiconducting. The d.c. conductivity ranged from 5×10–5 to 1.9×10–6 S cm–1 at 405 K for V2O5=60 mol% and MnO=0–20 mol%, and decreased with increasing MnO content. The conduction was confirmed to obey the adiabatic small polaron hopping model, and was due to mainly hopping between V-ions in the glasses. The polaron band width J was estimated to be J=0.10–0.20 eV. The electron–phonon interaction coefficient p was very large (21–26). The hopping mobility evaluated as 2.3×10–7–2.7×10–6 cm2 V–1 s–1 increased with increasing V2O5 content. The estimated carrier concentration was the order of 1019 cm–3. The principal factor determining conductivity was the polaron hopping mobility in these glasses. © 1998 Chapman & Hall     

Computer Simulation of Noncrystalline Ionic–Covalent Oxides CaO–P2O5

The semiclassical molecular dynamics simulation method proposed earlier for studying ionic–covalent oxide systems was applied to noncrystalline calcium phosphates. The expressions for the potentials of ionic–covalent bonds were found. Taking into account mixed bonding improves agreement with the experimental data on the density, energy, and structure of the condensed calcium phosphates. The charge on the phosphorus ion depends on its nearest neighbor environment and is 3.41 ± 0.19 in 3CaO · P₂O₅ and 3.54 ± 0.52 in CaO · 2P₂O₅. The simulated structures are rather loose and contain large voids.     

Development and bioactivity evaluation of bioglasses with low Na2O content based on the system Na2O–CaO–MgO–P2O5–SiO2

Osteoconductive bioglasses, free of K(2)O and Al(2)O(3) and with content of Na(2)O lower than 10?mol%, were designed based on the ratio (SiO(2)?+?MgO)/(P(2)O(5)?+?CaO?+?Na(2)O) in the system Na(2)O-CaO-MgO-P(2)O(5)-SiO(2). The developed glasses have shown a strong potential for the formation of hydroxycarbonated apatite (HCA) in vitro. The particles of HCA aggregates tend to be of finer size with increasing the ratio of (SiO(2)?+?MgO)/(CaO?+?P(2)O(5)?+?Na(2)O) in the glass chemical composition indicating significant bioactivity. Critical size bone defects created in the femurs of albino adult female rats, and grafted with the glass particles for 12?weeks post implantation, were completely healed by filling with mineralized bone matrix without infection showing a strong potential for new bone formation in vivo. Osteoblasts and osteocytes were observed close to the surface of the granular implants with active areas of bone deposition, resorption and remodelling. The bioglass with lowest (SiO(2)?+?MgO)/(CaO?+?P(2)O(5)?+?Na(2)O) ratio has shown the highest bioactivity while the bioglass with the highest (SiO(2)?+?MgO)/(CaO?+?P(2)O(5)?+?Na(2)O) has shown the lowest bioactivity. The newly formed bone in vivo has shown a similar structure to that of the original bone as indicated by the histology and microstructural results. In addition, Ca/P molar ratio of the newly formed bone was found to be (~1.67), which is similar to that of the original bone.     

Electrical conductivity studies of Bi2O3–Li2O–ZnO–B2O3 glasses

Ac conductivity measurements and its analysis has been performed on xBi₂O₃–(65?x)Li₂O–20ZnO–15B₂O₃ (0 ≤ x ≤ 20) glasses in the temperature range 30–300 °C and a frequency range of 100 Hz to 1 MHz. The dc conductivity increased and the activation energy decreased with lithium content. The frequency dependent conductivity has been analyzed employing conductivity and modulus formalisms. The onset of conductivity relaxation shifts towards higher frequencies with temperature. The Almond–West conductivity formalism is used to explain the scaling behavior, and the relaxation mechanism is independent of temperature.     

Characterisation of Ga2O3–Na2O–CaO–ZnO–SiO2 bioactive glasses

The structural role of Gallium (Ga) is investigated when substituted for Zinc (Zn) in a 0.42SiO₂–0.40–xZnO–0.10Na₂O–0.08CaO glass series, (where x = 0.08). Each starting material was amorphous, and the network connectivity (NC) was calculated assuming Ga acts as both a network modifier (1.23), and also as a network former. Assuming a network forming role for Ga the NC increased with increasing Ga concentration throughout the glass series (Control 1.23, TGa-1 2.32 and TGa-2 3.00). X-ray photoelectron spectroscopy confirmed both composition and correlated NC predictions. Raman spectroscopy was employed to investigate Q-structure and found that a shift in wavenumbers occurred as the Ga concentration increased through the glass series, from 933, 951 to 960 cm^?1. Magic angle spinning nuclear magnetic resonance determined a chemical shift from ?73, ?75 to ?77 ppm as the Ga concentration increased, supporting Raman data. These results suggest that Ga acts predominantly as a network former in this particular Zn-silicate system.     

BaWO4–BaCuO2–Y2Cu2O5–“1010” Section of the Y2O3–BaO–WO3–CuO System

The phase region of cubic perovskite-like solid solutions (a = 8.28–8.40 Å) in the Y₂O₃–BaO–WO₃–CuO system is outlined, and the phase compatibility diagram of the BaWO₄–BaCuO₂–Y₂Cu₂O₅–1010 (1010 = Y₂WO₆ + Y₂W₃O₁₂) is constructed.     

Influence of different nucleating agent additives on phase structure and ferroelectric properties of SrO–BaO–Nb2O5–CaO–SiO2–B2O3 glass-ceramics

Ferroelectric glass-ceramics of the SrO–BaO–Nb₂O₅–CaO–SiO₂–B₂O₃ system with different nucleating agents Cr₂O₃, BaF₂, ZrO₂, CaF₂ and CeO₂, have been prepared by conventional melt casting followed by controlled crystallization processing. The effect of different nucleating agent additions on crystallization mechanism, crystallization behaviors, microstructures and dielectric properties of the glass-ceramics are studied using DTA, XRD techniques, SEM and LCR analyzer. The results show that the addition of different nucleating to the glass-ceramics decreases the crystallization temperatures, accelerates the secondary phase elimination and promotes the uniform distribution of grain size. The well development of microstructure promoted by the nucleating agents can result in the improvement of the dielectric constant as well as energy storage density remarkably. The sample with CeO₂ as the optimum nucleating agent achieves the dielectric constant of 301, breakdown strength of 622 kV/cm and the highest energy storage density of 5.15 J/cm³.