Effect of the addition of Fe2O3 and heat treatment duration on the magnetic susceptibility of V2O5-P2O5-B2O3 glass system

The effect of the addition of Fe₂O₃ and heat treatment duration on the magnetic susceptibility of vanadium borophosphate glass were studied. The magnetic susceptibility of glass samples was found to increase with increasing Fe₂O₃ content, which may be explained by the formation of the FeO₆ group and the change of Fe²⁺ to Fe³⁺ which has higher paramagnetic properties. No detectable changes in the magnetic susceptibility with heat treatment for the samples containing 0.0, 0.5 and 1.0 mol% Fe₂O₃ was observed. The magnetic susceptibility for the heat treated samples containing 2.5, 5.0 and 7.5 mol% Fe₂O₃ decreases sharply with increasing duration of heat treatment up to 6 h and then remains almost constant. The sharp decrease in magnetic susceptibility of 2.5 mol% Fe₂O₃ is attributed to the increase in the number of ferrous ions. The sharp decrease for samples containing 5.0 and 7.5 mol% Fe₂O₃ is attributed to the increase in the number of Fe³⁺ in tetrahedral co-ordination. The rate of crystallization owing to the heat treatment was calculated and was found to increase with increasing iron oxide content. The geometry of crystallization was found to be in three-, two-and one-dimension(s) for samples containing 2.5, 5.0 and 7.5 mol% Fe₂O₃, respectively.     

Structural investigation of xFe2O3 · (100 − x)[P2O5 · TeO2] glass system by FT-IR study and EPR spectroscopy

Glasses from xFe₂O₃ · (100 − x)[P₂O₅ · TeO₂] system, with 0 ≤ x ≤ 50 mol%, were investigated by X-ray diffraction, FT-IR and EPR spectroscopies. The XRD patterns show a vitreous state of studied samples for x ≤ 35 mol% Fe₂O₃. The FT-IR spectrum of the P₂O₅ · TeO₂ glass matrix reveals a structure formed from PO₄, TeO₄ and TeO₃ units. The addition and the increasing of Fe₂O₃ content modify progressively the structure of the glass matrix. The local structure in the investigated glasses was revealed by means of EPR using Fe³⁺ (3d⁵; ⁶S_5/2) ions as paramagnetic probes. The EPR spectra present two resonance absorption lines characteristic to Fe³⁺ ions centred at g_eff ≈ 2.0, for 0.5 ≤ x ≤ 35 mol% and g_eff ≈ 4.3, for 0.5 ≤ x ≤ 5 mol%. The variation of the EPR parameters, the intensity and line-width of these absorption lines, with iron ions composition has been followed.     

Structural properties of lead vanadate glasses containing La3+ or Fe3+ ions

Structural properties of lead vanadate glasses containing La³⁺ or Fe³⁺ ions were investigated using X-ray diffraction, Fourier transform infrared spectroscopy and laser Raman spectroscopy. Crystalline Pb₂V₂O₇ was formed for the molar composition 66.7PbO-33.3V₂O₅. Incorporation of greater quantities of La³⁺ into lead metavanadate glass caused the crystallization of Pb₂V₂O₇. Fourier transform infrared and laser Raman spectra also suggested the presence of LaVO₄. Incorporation of Fe³⁺ ions into lead metavanadate glass, up to 20 wt% Fe₂O₃, did not cause crystallization inside the glass matrix. Changes in the vibrational spectra are discussed.     

Infrared study of the effect of heat treatment and irradiation on barium borate glass containing iron

A barium borate glass system was prepared containing different amounts of iron. The prepared glasses were heat treated at 550° C for 2, 6, 12, 18 and 24 h. Also the glasses were irradiated usingψ-ray at a dose of 4.805 × 10₄rad h⁻¹ for 12, 18 and 24 h. The infrared spectra were recorded for the untreated and heat treated samples. It was found that, when the Fe₂O₃ was introduced in the glass the triangle BO₃ groups were transferred to BO₄ groups. The formation of non-bridging oxygen with high concentration was also observed as a result of introducing Fe₂O₃ in the glass. The absorption bands of the IR spectra of the irradiated samples indicated no significant variations, and only a transfer of some BO₄ groups to BO₃ groups could be observed.     

Some physical properties of V2O5-Fe2O3 and V2O5-Fe2O3-Li2O systems

Various methods have been used to study the physical properties of the V₂O₅-Fe₂O₃ and V₂O₅-Fe₂O₃-Li₂O systems, including X-ray, electron microscope, Mössbauer effect, NMR and thermogravimetric measurements. The iron ions are approximately equally distributed in substitutional and interstitial sites in the V₂O₅ lattice. The maximum number of iron ions dissolved in the V₂O₅ matrix corresponds to 4 mol % Fe₂O₃. In all the samples a quantity of Fe₂O₃ which has not been included in lattice is observed. The V₂O₅-Fe₂O₃ and V₂O₅-Fe₂O₃-Li₂O systems are formed from solid solutions mixed with very small Fe₂O₃ particles. The analysis of the charge compensation of iron ions suggests that V₂O₅ is a quasi-amorphous semiconductor. Irradiation of V₂O₅-based samples with an electron beam induces the V₂O₅ platelets to convert to the VO _x phase.     

Magnetic bioactive glass ceramic in the system CaO-P2O5-SiO2-MgO-CaF2-MnO2-Fe2O3 for hyperthermia treatment of bone tumor

Magnetic bioactive glass ceramic (MG) in the system CaO–SiO₂–P₂O₅–MgO–CaF₂–MnO₂–Fe₂O₃ for hyperthermia treatment of bone tumor was synthesized. The phase composition was investigated by XRD. The magnetic property was measured by VSM. The in vitro bioactivity was investigated by simulated body fluid (SBF) soaking experiment. Cell growth on the surface of the material was evaluated by co-culturing osteoblast-like ROS17/2.8 cells with materials for 7 days. The results showed that MG contained CaSiO₃ and Ca₅(PO₄)₃F as the main phases, and MnFe₂O₄ and Fe₃O₄ as the magnetic phases. Under a magnetic field of 10,000 Oe, the saturation magnetization and coercive force of MG were 6.4 emu/g and 198 Oe, respectively. After soaking in SBF for 14 days, hydroxyapatite containing CO₃ ²⁻ was observed on the surface of MG. The experiment of co-culturing cells with material showed that cells could successfully attach and well proliferate on MG.     

Effect of heat treatment and irradiation on electrical conductivity and crystallization in the BaO-B2O3-Fe2O3 glass system

A glass system was prepared according to the formula 75 mol % B₂O₃-(25 –x) mol % BaO –x mol % Fe₂O₃, wherex = 0, 1, 2.5, 5, 7.5 and 10. The glasses were subjected to heat treatment at 550° C for 2, 6, 12, 18 and 24 h. The glasses were also irradiated using-rays at a dose of 4.805 × 10⁴ rad h^–1 for 12, 18 and 24 h. An X-ray diffraction technique was used to identify the separated crystalline phases. The electrical conductivity and activation energy of untreated, heat-treated and irradiated samples were measured and calculated. The rate and the dimensions of crystallization were also calculated by using the Avrami equation. It was found that-Fe₂O₃ is the separated phase when a sample containing 7.5 mol% Fe₂O₃ is heat treated for 24h;-Fe₂O₃ and Fe₂O₃ are the separated phases when the sample containing 10 mol% Fe₂O₃ is heat treated for 6, 12 and 18 h, with the addition of BaO when the sample is heat treated for 24 h. A miminum value for the electrical conductivity of glass samples was found to occur around an Fe₂O₃/BaO ratio of 0.425. The rate of crystallization in the sample containing 10 mol% Fe₂O₃ is 1.30607 × 10^–3 and the geometry of crystallizationn is 1.2238, which indicates that the crystallization was in one dimension.     

Spectroscopic,electrical and EPR studies of binary semiconducting oxide glasses containing 50 mol% V2O5

Recent measurements on the V₂O₅-GeO₂ glass system consisting of an equimolar mixture of V₂O₅ and GeO₂ revealed that increase in electrical conductivity of these glasses upon annealing could be attributed to the increase in V⁴⁺ and V³⁺ content which accompanied the microstructure formation. In the present work we report a similar study on V₂O₅-TeO₂ and V₂O₅-P₂O₅ glass systems. It was found that in tellurite glass V³⁺ content increased upon annealing and V⁴⁺ content remained unchanged. In phosphate glass some increase in V⁴⁺ and no significant change in V³⁺ contents were observed. V³⁺ and V⁴⁺ contents in glasses could be best estimated from optical and electron paramagnetic resonance spectra, respectively.     

Optical absorption and electron spin resonance studies of Cu2+ in Li2O-Na2O-B2O3-As2O3 glasses

The local structure around Cu²⁺ ion has been examined by means of electron spin resonance and optical absorption measurements in xLi₂O-(40-x)Na₂O-50B₂O₃-10As₂O₃ glasses. The site symmetry around Cu²⁺ ions is tetragonally distorted octahedral. The ground state of Cu²⁺ isd _x ²−y ².The glass exhibited broad absorption band near infrared region and small absorption band around 548 nm, which was assigned to the ²B_1g →²E_g transition.     

Effect of annealing on d.c. conductivity of V2O5-SnO-TeO2 glasses

The d.c. conductivity (σ) of V₂O₅-SnO-TeO₂ glasses prepared by the press-quenching method was studied at temperatures from room temperature (RT) to 473 K, and the effect of annealing on σ was investigated. The conductivity of 50V₂O₅·20SnO·30TeO₂ glass was determined to be 3.98×10⁻⁴ Scm⁻¹ at 473 K and was unchanged for annealing (6–48 h) at 493 K, lower than T_g = 501 K, while its density increased with annealing time. These glasses were found to be n-type semiconductors, and the conduction was confirmed to be due to adiabatic small polaron hopping for V₂O₅ ≧ 50 mol%, and non-adiabatic for V₂O₅ < 50 mol%. The activation energy for conduction, W, decreased with annealing time. Variations in oxygen molar volume of the glasses with annealing time inferred a change in glass structure, from loosely to closely packed, resulting in a decrease in vanadium ion spacing with annealing. This caused an increase in the polaron band width, producing a decrease in polaron hopping energy and W. The effect of annealing time on the density of 50V₂O₅·20SnO·30TeO₂ glass was explained adequately by Winter's formula.     

Structural changes induced by Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> addition in strontium-borate glass matrix

Glasses of the xFe₂O₃·(100−x)[B₂O₃·SrO] system, with 0 ≤ x ≤ 30 mol% were studied by X-ray diffraction, density, optical microscopy and FT-IR spectroscopy measurements. The X-ray patterns for the prepared system show that vitreous phase is present only in the sample with x < 40 mol%. For x ≥ 40 mol% in the studied samples is evidenced crystalline phase of Fe₂O₃. SEM measurements for the sample with x = 40 mol% shows that there are formed Fe₂O₃ microcrystallites with 10–20 μm dimension. FT-IR spectroscopy measurements shown that BO₃ and BO₄ are the main structural units of the glass system and the iron ions are located in the glass network.     

Preparation and characterization of binary V2O5-Bi2O3 glasses

Characterization of the binary V₂O₅-Bi₂O₃ glasses prepared by rapidly quenching the melt has been made from the studies of X-ray diffraction, scanning electron microscopy, infrared absorption, differential thermal analysis, electron paramagnetic resonance, chemical analysis, density and electrical properties. Stable glasses are obtained for 95 to 75 mol % V₂O₅ by quenching on a stainless steel substrate, while quenching on a copper substrate extends the glass formation range from 95 to 70 mol % V₂O₅. The V-O bond vibration in the glasses occurs at 1020 cm^–1 and the V^5% ion exists in six-fold coordination as in crystalline V₂O₅. All the glasses appear to be in single phase. The spin concentration in the glasses is found to be independent of temperature. A second heat-treatment at 255° C develops crystalline phase in the glasses. Unlike infrared absorption, electron paramagnetic resonance, density and chemical compositions, the electrical and thermal (DTA) properties are found to be slightly sensitive to the thermal history of preparation of the glasses. The high-temperature (300 to 500 K) conduction in the glasses seems to be due to adiabatic hopping of polarons. The thermopower is observed to be independent of temperature and provides evidence for small polaron formation in the glasses.     

Low temperature synthesis of glassy solids of the system Al2O3-P2O5-SiO2

Glassy solids of the system Al₂O₃-P₂O₅-SiO₂, which have not been obtainable because of the devitrification of glass during the cooling process after melting, were obtained by the gel method. After the gels of the system Al₂O₃-P₂O₅-SiO₂ were prepared from AlCl₃·6H₂O, H₃PO₄ and Si(OC₂H₅)₄, they were heat treated up to 800° C to obtain glassy solids. In SiO₂ concentrations ranging from 75 to 82 mol % in batch compositions, non-porous transparent solids were obtained, while in SiO₂ concentrations above 87 mol %, porous transparent solids were obtained. Tridymite was precipitated because of the crystallization of glassy solids during heat treatment above 800° C. It depended upon the microstructure of the gels whether non-porous glassy solids were obtained or not. The thermal expansion coefficients of the glassy solids were greatly dependent upon the concentration of P₂O₅, ranging from 1.7×10⁻⁶ to 4.2×10⁻⁶ (1/° C).     

Novel structural properties of the lead–vanadate–tellurate glass ceramics

In this paper, we have examined and analyzed the effects of systematic intercalation of the lead ions on vanadate–tellurate glass ceramics with interesting results. The structural properties of the lead–vanadate–tellurate glass ceramics of compositions xPbO·(100 − x)[6TeO₂·4V₂O₅], x = 0 − 100 mol%, are reported for the first time. It has been shown by X-ray diffraction that single-phase homogeneous glasses with a random network structure can be obtained in this system. Among these unconventional lead–vanadate–tellurate glass ceramics, we found that network formers are good host material for lead ions and are capable to intercalate a variety of species such as Te₂V₂ ⁵⁺O₉, Pb₃(V⁵⁺O₄)₂, Pb₂V₂ ⁵⁺O₇, and V₂O₅-rich amorphous phase. On the other hand, these glass ceramics contain V⁴⁺ and V⁵⁺ ions necessary for the electrical conduction. Based on these experimental results, we propose that the V⁴⁺=O bonds are created by two different mechanisms: the first of reduction of V⁵⁺ ions to V⁴⁺ ions and thus of creation of V⁴⁺=O bonds.     

Oxygen gas-sensing behaviour of V2O5–SnO–TeO2 glass

The d.c. conductivity, σ, and the oxygen gas-sensing behaviour of V₂O₅–SnO–TeO₂ glass prepared by press-quenching were studied in argon and oxygen gas atmospheres at temperatures ranging from 303–473 K. The glass of 50V₂O₅·20SnO·30TeO₂ (mol %) was n-type semiconducting. The high-temperature conductivity was lower in oxygen and higher in argon than that in air. This was explained by the V⁴⁺ ions in the glass being oxidized by oxygen which had diffused into the glass, resulting in an increase in V⁵⁺ with time. The experimental relationship between σ and oxygen partial pressure, P _O2, agreed quantitatively with the theoretical relation σ ∝ P _O2 ^-1/4 . Changes in conductivity by switching the atmospheres between oxygen and argon gases were found to be reproducible. From the data of these dynamic changes, the oxygen gas sensitivity, S, at 473 K was obtained to be 1.3 in oxygen atmosphere. The dynamic changes could be quantitatively explained by an oxygen diffusion model. Throughout these discussions, the present tellurite glass was found to possess a potential applicability as an oxygen gas sensor. This revised version was published online in November 2006 with corrections to the Cover Date.     

Magnetic properties of the phases Fe2V4O13, FeVMoO7 and Fe4V2Mo3O20

The Curie constant,C, Weiss constant, , effective magnetic moment, _eff, and spectroscopic splitting factor,g, were determined for the Fe³⁺ ions in Fe₂V₄O₁₃, FeVMoO₇ and Fe₄V₂Mo₃O₂₀ at 76–300 K based on measurements of magnetic susceptibility of the phases. The Neel temperature,T _N, of interest was based on the temperature dependence of magnetization of the phases. It was shown that a local antiferromagnetic arrangement of the Fe³⁺ ions in Fe₂V₄O₁₃, FeVMoO₇ and Fe₄V₂Mo₃O₂₀ is already involved at a temperature much higher than the Neel temperature, resulting from the cation-anion-cation superexchange between the Fe³⁺ ions with ad ⁵ configuration.     

Thermal expansion of silico-phosphate glasses with small additions of Fe2O3: EPR and dilatometric studies

Electron paramagnetic resonance (EPR) and dilatometric measurements in phosphosilicate glass have been made in order to elucidate an anomalous trend of the linear thermal expansion coefficientβ when Fe₂O₃ was added to the composition. The g≃2 and g_eff≃4.27 EPR lines were attributed, respectively, to undistorted and octahedrally coordinated Fe³⁺ ions, and to Fe³⁺ ions in low symmetry (rhombic) sites. The Fe³⁺ ion distribution in the network at different temperatures has been explained by a model of chemical insertion and it has been proved that the Fe³⁺ ions have two kinds of role as network modifiers. A relationship has also been found betweenβ and the amounts of Fe₂O₃ added in the range 0 to 12 wt %. It is with deep regret that we note the death of Professor G. L. Del Nero.     

Crystallization and wetting of ZnO-Al2O3-B2O3-SiO2 glass-ceramic for sealing to Kovar alloy

A new type of ZnO-Al₂O₃-B₂O₃-SiO₂ glassceramics seals to Kovar in electronic packaging was developed, whose coefficient of thermal expansion (CTE) and electrical resistance were 5.2 × 10⁻⁶/°C and over 1 × 10¹³ Ω·cm, respectively. The major crystalline phases in the glass-ceramics seals were ZnAl₂O₄, ZnB₂O₄ and NaSiAl₂O₄. The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of the alkali metal ions into the crystal lattices. It was found that the crystallization happened first on the surface of the sample, leaving the amorphous phase in the inner parts, which makes the glass suitable for sealing. The glass-ceramic showed better wetting on the Kovar surface, and sealing atmosphere and temperature showed great effect on the wetting angle. Strong interfacial bonding was obtained, which was mainly attributed to the interfacial reaction between SiO₂ and FeO or Fe₃O₄. This paper was presented at 2008 MRS International Materials Research Conference and won the student best paper award of the conference.     

Relaxor ferroelectric-like behavior in 10PbTiO3–10Fe2O3–30V2O5–50B2O3 glass for energy storage applications

Recently, demand increased for dielectric materials used in energy storage devices at high voltage applications. Appearance of polar clusters in glass matrix could promote its use in energy storage applications. Conventional quenched glass sample of composition 10PbTiO₃–10Fe₂O₃–30V₂O₅–50B₂O₃ were successfully developed. The glassy nature was confirmed by XRD and DSC measurements. Boson peak observed at low frequency from the Raman spectra confirms polar cluster formation. Dielectric properties of prepared glass were investigated in a wide range of frequency and temperature. Broad and diffuse peak of dielectric permittivity shifted to the higher temperatures, denoting the typical relaxor ferroelectrics like behavior. Sample shows energy storage density of about 164.7 mJ/cm³ at room temperature. Quenched glass sample shows typical anti-ferromagnetic behavior.

     

Chemical and structural properties of the system Fe2O3-Cr2O3

Chemical and structural properties of the mixed metal oxides (1–x)Fe₂O₃+xCr₂O₃ were studied by different techniques. X-ray powder diffraction showed the existence of solid solutions, (Fe_1–x Cr _x )₂O₃, over the whole concentration region, 0x1. The gradual replacement of Fe³⁺ with Cr³⁺ ions in samples prepared at 900°C caused changes in unit-cell parameters; most of these changes took place in the region fromx0.3–0.9. The samples having the fraction of Cr₂O₃ in the region from 0.7–0.8, contained two closely related phases, with slightly different compositions. After an additional heat treatment at 1100°C, these samples contained only one phase.⁵⁷Fe Mössbauer spectroscopy showed a gradual decrease of hyperfine magnetic field with increasing Cr₂O₃ content. The sample having the fraction of Cr₂O₃ of 0.7, and prepared at 900°C, exhibited two separated sextets at room temperature, in comparison with other compositions showing one sextet. It was shown that Fourier transform infrared (FT-IR) spectroscopy is a powerful method for the investigation of structural changes in these solid solutions. The increase in the Cr₂O₃ content resulted in shifts of the corresponding infrared bands. In addition, a gradual transition of the spectrum typical for -Fe₂O₃ to the spectrum typical for Cr₂O₃ was shown. The transition effects observed in the FT-IR spectra were correlated with the X-ray powder diffraction and⁵⁷Fe Mössbauer spectroscopic results.