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.     

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.     

Magnetic Susceptibilities of MgCu2O3 and Doped MgCu2O3 with Zn and Co

The magnetic susceptibility of MgCu ₂ O ₃ powder was measured between 0.2 K and 800 K. The results above TN can be fitted by a Curie–Weiss law plus a one-dimensional (1 — d) antiferromagnetic susceptibility and a constant susceptibility. Below TN the magnetic susceptibility has the large contribution from the paramagnetic impurity of free Cu ²⁺ ions in the compound. When we add Zn ²⁺ ions in the compound the Néel temperature decreases. On the other hand the Co doped MgCu ₂ O ₃ enhance the Néel temperature. Only a small number of Co ions changes the magnetic property of MgCu ₂ O ₃ drastically.     

Preparation of a very pure Fe2O3·xH2O gel: some structural and magnetic properties

A gel of iron (III) oxide hydrate was prepared using the oxidation of a FeC₂O₄· 2H₂O suspension with H₂O₂. Alkaline ions were not employed for the precipitation of the gel and the C₂O ₄ ^2– anions which are oxidized to CO₂ disappear rapidly from the solution. A very pure Fe₂O₃·xH₂O gel is thus obtained. X-ray diffraction and electron microscope studies showed the very little crystalline character of this gel and the different steps of its dehydration and crystallization with increasing temperature. Magnetic measurements at low temperature revealed the remarkable properties of this amorphous Fe₂O₃·xH₂O: superparamagnetism, blocking temperature, T _B, and thermo-remanent magnetization. These properties are characteristic of fine grains and mictomagnetic compounds.     

Magnetization, magnetic susceptibility, and effective magnetic moment of the Fe3+ ions in Bi2Fe4O9

Bi₂Fe₄O₉ with an orthorhombic structure and lattice parameters a = 7.9595 Å, b = 8.4297 Å, c = 5.9912 Å, and V = 401.987 ų has been prepared by solid-state reactions method. Its molar magnetic susceptibility measured as a function of temperature in the range 5–950 K indicates that Bi₂Fe₄O₉ is an antiferromagnet with a Néel temperature of 258 K. In the range 280–750 K, its molar magnetic susceptibility exhibits Curie-Weiss behavior, which allowed us to determine the Weiss constant (Θ = ?1468 K) of this material and the effective magnetic moment of the Fe³⁺ ions $\left( {\mu _{eff}^{Fe^{3 + } } = 6.37\mu _B } \right)$ . Magnetization versus magnetic field data show no magnetic hysteresis, indicating that the Bi₂Fe₄O₉ sample studied exhibits no weak ferromagnetism.     

Solid state reactions in the Fe2O3-CaCO3-In2O3 system

The kinetics of solid-state reactions of powdered reactants were investigated by X-ray and by differential thermogravimetry in a magnetic field. Measurements revealed mutual diffusion of the Fe³⁺ and In³⁺ ions in the Fe₂O₃-In₂O₃ system heat treated for 3 h at 700 to 1400° C. Diffusion of indium into the Fe₂O₃ lattice caused a shift of the Curie temperature of the antiferromagnetic iron oxide towards lower temperatures. Only Caln₂O₄ was found between CaCO₃ and In₂O₃ up to 1400° C. Also, in the Fe₂O₃-CaCO₃-In₂O₃in system, the reaction started with the mutual diffusion of iron and indium and the forming of CaFe₂O₄. End-products were the magnetic -Ca₄Fe₁₄O₂₅ and CaFe₄O₇, and the non-magnetic CaFe₅O₇, depending on the In³⁺ concentration. Indium stabilized the magnetic calcium-iron oxide structures, shifting their Curie temperatures towards lower values.     

Dielectric characteristics of composite ceramics in the Ba(Mg1/3Ta2/3)O3-BaO · Nd2O3 · 5TiO2 system

Dielectric characteristics of composite ceramics in the system Ba(Mg_1/3Ta_2/3)O₃-BaO · Nd₂O₃ · 5TiO₂ were investigated to search for a new candidate system for microwave dielectric ceramics with modifiable dielectric constant, low dielectric loss and small temperature dependence. The dielectric constant could be adjusted in the range 25–81 by controlling the concentration of BaO · Nd₂O₃ · 5TiO₂, while the dielectric loss remained of the order of 10^–4 for some compositions. Moreover, the dielectric properties in the present system could be significantly improved by post-densification thermal treatment.     

Magnetic susceptibility of amorphous and heat-treated vanadate glasses

X-ray diffraction and magnetic susceptibility measurements were used to study the effect of addition of iron on the crystallization process and magnetic properties of the vanadium borophosphate system before and after heat treatment. The glass composition was 78 mol% V₂O₅-15 mol% P₂O₅-7 mol% B₂O₃, the Fe₂O₃ was added with concentration ranging from 0.05 up to 1 mol%. The X-ray diffraction showed that the V₂O₅ was the only phase separated during the heat treatment process. The intensity of the characteristic V₂O₅ peaks increased with increasing Fe₂O₃ content. The magnetic susceptibility was found to decrease for the sample containing 0.05 mol% Fe₂O₃. This could be explained by the presence of most of the iron ions in the ferrous state and the presence of a covalent bond between the ferrous ions and the oxygen ions. An increase in the magnetic susceptibility was found in samples containing an iron content of more than 0.05. This increase could be explained according to the change of Fe²⁺ ions to Fe³⁺ which has higher paramagnetic behaviour.     

The constituents of BaO·5.5 Fe2O3 magnets

Because BaO·5.5 Fe₂O₃ magnets have higher (B_dH_d)_m values than comparable BaFe₁₂O₁₉ products, magnetic phase analyses were made to find the reason for this characteristic difference. These analyses led to the discovery of a new complex ferrite, BaFe_IVB=Ba₃Fe₄ ²⁺Fe₂₈ ³⁺O₄₉. Specimens of this material were found to have the following characteristics at room temperature: 4M _s=5000 G andH ^A=19.3 kOe. The Curie temperature is 451 ° C. These analyses indicated that BaO·5.5 Fe₂O₃ specimens are comprised of 1/3 part BaFe₁₂O₁₉ and 2/3 part BaFe_IVB by weight. This explains why BaO·5.5 Fe₂O₃ magnets have higher (B_dH_d)_m values than comparable BaFe₁₂O₁₉ products.     

Preparation of B2O3-P2O5-SiO2 coating films by the sol-gel method

ThexB₂O₃ · (20-x) P₂O₅ · 80SiO₂ (in mol%) glass films withx=0, 10 and 20 have been prepared from metal alkoxides by carrying out the coating in a dry atmosphere. These coating films have shown a larger value of load at scratch and a smaller shrinkage during heat-treatment by replacing P₂O₅ in the films with B₂O₃. It has been found that B₂O₃ more effectively reduces the glass transition temperature of SiO₂ glass than P₂O₅. The concentrations of sodium ions, which migrated from soda-lime-silica glass substrates during the film formation, were higher in phosphosilicate and borophosphosilicate films than in borosilicate and pure silica films. This finding should be ascribed to the gettering effects of phosphorus for sodium ions.     

The crystallization of Gd2 3 -Al2O3 glasses

Glasses of Gd₂O₃ · x Al₂O₃ compositions where x represents 5/3, 4 and 6, were prepared using a rapid quenching apparatus and a laser beam. The crystallization process of the glasses was studied by means of differential thermal analysis (DTA), X-ray diffraction analysis and electron microscopy. The crystallizations of Gd₂O₃ · 5/3Al₂O₃, Gd₂O₃ · 4Al₂O₃ and Gd₂O₃ · 6Al₂O₃ are complex and exhibit one, two and three exothermic peaks in DTA measurement with increasing Al₂O₃ concentration, respectively. The crystallization process of Gd₂O₃ · 5/3Al₂O₃ glass involved the direct formation of the gadolinium aluminium garnet, 3Gd₂O₃ · 5l_{2 3} (GdAG), which is not obtained by the ordinary solid phase reaction. After crystallization of Gd₂O₃ · 4Al₂O₃ and Gd₂O₃ · l_{2 3} glass, both phases become a mixture of Gd₂O₃ · Al₂O₃ (perovskite type) and -Al₂O₃.     

Rare-gas mobility in some anisotropic ceramic oxides: Al2O3, Cr2O3, Fe2O3, TiO2, U3O8

The mobility of the inert gases xenon or radon in five anisotropic oxides (hexagonal corundum Al₂O₃, Cr₂O₃, Fe₂O₃, tetragonal rutile TiO₂, and orthorhombic U₃O₈) was studied. The gases were introduced by ion bombardment. The oxides were in the form of powders, sinters, or single crystals. Normal volume diffusion was found at low gas concentration, the activation energies in kilocalories per mole being 85 for Al₂O₃, 73±5 for Cr₂O₃, 68±5 for Fe₂O₃, 78±5 for TiO₂, and 85±8 for U₃O₈, and the pre-exponential termsD ₀ falling into the ideal range of about 3×10^–1±1 cm²/sec. Structural radiation damage, the annealing of which coincided with gas release at low temperatures, and, in some cases, retardation of the gas release were found at higher gas concentrations. Some evidence is presented that grain boundaries, pre-existing vacancy clusters, and dislocation loops may act as trapping sites for gas atoms (or bubbles) and may be stabilised after trapping of the gas.     

Magnetic Properties of Some Tellurite Glasses

The AC magnetic susceptibility in the range 5–130 K of the tellurite glass systems: TeO₂–MnO₂–ZnO–PbO and TeO₂–MnO₂–V₂O₅–Fe₂O₃ was measured and analyzed. The investigations of the AC magnetic susceptibility facilitated the determination of the molar susceptibility, paramagnetic magnetic susceptibility, paramagnetic Curie temperature, and magnetic entropy changes of the tellurite glasses. The results clarified that the temperature dependence of the magnetic susceptibility deviated from the Curie law and the increase of the small negative values of Curie temperature indicated negative interchange interactions between the antiferromagnetically coupled manganese ions within the present glass network. The magnetic moments evaluated from susceptibility measurements of the glasses show the predominance of the Mn²⁺ valence state than Mn³⁺ valence state of MnO₂.     

Role of chromium ion valence states in ZnO-As2O3-Sb2O3 glass system by means of spectroscopic and dielectric studies

ZnO-Sb₂O₃-As₂O₃ transparent glasses containing small concentrations of chromium ions (introduced as Cr₂O₃) ranging from 0 to 0.2 mol% is prepared. A number of studies viz., XRD, SEM, DTA, optical absorption, FT-IR, Raman, ESR spectra, magnetic susceptibility and dielectric properties (constant ?′, loss tan δ, ac. conductivity σ_ac over a wide range of frequency and temperature as well as dielectric breakdown strength at room temperature) of these glasses have been carried out as a function of chromium ion concentration. The results have been analysed in the light of different oxidation states of chromium ions. The analyses indicates that when the concentration of chromium ions is low, these ions mostly exist in Cr⁶⁺ and Cr⁵⁺ states, occupy network forming positions with CrO₄²⁻ and CrO₄³⁻ structural units respectively and increase the rigidity of the glass network. When the concentration of chromium ions is gradually increased, these ions seem to be existing mostly in Cr³⁺ state.     

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.     

Magnetic and luminescent properties of Fe3O4@Y2O3:Eu3+ nanocomposites

The multifunctional Fe₃O₄@Y₂O₃:Eu³⁺ nanocomposites were prepared by a facile solvothermal method with Fe₃O₄ nanoparticles as the core and europium-doped yttrium oxide (Y₂O₃:Eu³⁺) as the shell. It is shown that Fe₃O₄@Y₂O₃:Eu³⁺ nanocomposites have a strong photoluminescence and special saturation magnetization Ms of 6.1 emu/g at room temperature. The effects of the magnetic field on the luminescence intensities of the nanocomposites are being discussed. The multifunctional nanocomposites with magnetic resonance response and fluorescence probe properties may be useful in biomedical applications, such as cell separation and bioimaging.     

Mixed alkali effect in Li2O–Na2O–B2O3 glasses containing Fe2O3—An EPR and optical absorption study

This paper reports the interesting results on mixed alkali effect (MAE) in xLi₂O–(30-x)Na₂O–69.5B₂O₃ (5 ≤ x ≤ 28) glasses containing Fe₂O₃ studied by electron paramagnetic resonance (EPR) and optical absorption techniques. The EPR spectra in these glasses exhibit three resonance signals at g = 7.60, 4.20 and 2.02. The resonance signal at g = 7.60 has been attributed to Fe³⁺ ions in axial symmetry sites whereas the resonance signal at g = 4.20 is due to isolated Fe³⁺ ions in rhombic symmetry site. The resonance signal at g = 2.02 is due to Fe³⁺ ions coupled by exchange interaction. It is interesting to observe that the number of spins participating in resonance (N) and its paramagnetic susceptibility (χ) exhibits the mixed alkali effect with composition. The present study also gives an indication that the size of alkali ions we choose in mixed alkali glasses is also an important contributing factor in showing the mixed alkali effect. It is observed that the variation of N with temperature obeys Boltzmann law. A linear relationship is observed between 1/χ and T in accordance with Curie–Weiss law. The paramagnetic Curie temperature (θ_p) is negative for the investigated sample, which suggests that the iron ions are antiferromagnetically coupled by negative super exchange interactions at very low temperatures. The optical absorption spectra exhibit only one weak band corresponding to the transition ⁶A_1g(S) → ⁴A_1g(G); ⁴E_g(G) at 446 nm which is a characteristic of Fe³⁺ ions in octahedral symmetry.     

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.

     

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.