Effects of Nb2O5 Replacement by Er2O3 on elastic and structural properties of 75TeO2-(10 − x)Nb2O5-15ZnO-(x)Er2O3 glass

Tellurite 75TeO₂-(10 − x)Nb₂O₅-15ZnO-(x)Er₂O₃; (x = 0.0-2.5 mol%) glass system with concurrent reduction of Nb₂O₅ and Er₂O₃ addition have been prepared by melt-quenching method. Elastic properties together with structural properties of the glasses were investigated by measuring both longitudinal and shear velocities using the pulse-echo-overlap technique at 5 MHz and Fourier Transform Infrared (FTIR) spectroscopy, respectively. Shear velocity, shear modulus, Young's modulus and Debye temperature were observed to initially decrease at x = 0.5 mol% but remained constant between x = 1.0 mol% to x = 2.0 mol%, before increasing back with Er₂O₃ addition at x = 2.5 mol%. The initial drop in shear velocity and related elastic moduli observed at x = 0.5 mol% were suggested to be due to weakening of glass network rigidity as a result of increase in non-bridging oxygen (NBO) ions as a consequence of Nb₂O₅ reduction. The near constant values of shear velocity, elastic moduli, Debye temperature, hardness and Poisson's ratio between x = 0.5 mol% to x = 2.0 mol% were suggested to be due to competition between bridging oxygen (BO) and NBO ions in the glass network as Er₂O₃ gradually compensated for Nb₂O₅. Further addition of Er₂O₃ (x > 2.0 mol%) seems to further reduce NBO leading to improved rigidity of the glass network causing a large increase of ultrasonic velocity (v_L and v_S) and related elastic moduli at x = 2.5 mol%. FTIR analysis on NbO₆ octahedral, TeO₄ trigonal bipyramid (tbp) and TeO₃ trigonal pyramid (tp) absorption peaks confirmed the initial formation of NBO ions at x = 0.5 mol% followed by NBO/BO competition at x = 0.5-2.0 mol%. Appearance of ZnO₄ tetrahedra and increase in intensity of TeO₄ tbp absorption peaks at x = 2.0 mol% and x = 2.5 mol% indicate increase in formation of BO.     

Investigation of the structure evolution process in sol-gel derived CaO-B2O3-SiO2 glass ceramics

A sol-gel method was used to prepare CaO-B₂O₃-SiO₂ (CBS) glass powder for making low-temperature cofired ceramics. This paper was focused on the mechanism of hydrolysis and polymerization and also on the structural evolution of xerogel at various temperatures. The xerogel was transformed into glass ceramics containing CaSiO₃ and CaB₂O₄ crystalline phases through nucleation and crystallization processes. The results indicated that the xerogel exhibits [BO₄] or [SiO₄] based three-dimensional network structure whose interstices Ca ions fill in, which becomes more orderly and stable after heat treatments. The CBS glass ceramics through controlled crystallization have a potential as electronic packaging materials.     

Crystallization kinetics in Cu46Zr45Al7Y2 bulk metallic glass by differential scanning calorimetry (DSC)

Crystallization transformation kinetics in isothermal and non-isothermal (continuous heating) modes were investigated in Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass by differential scanning calorimetry (DSC). In isochronal heating process, activation energy for crystallization at different crystallized volume fraction is analyzed by Kissinger method. Average value for crystallization in Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass is 361 kJ/mol in isochronal process. Isothermal transformation kinetics was described by the Johnson-Mehl-Avrami (JMA) model. Avrami exponent n ranges from 2.4 to 2.8. The average value, around 2.5, indicates that crystallization mechanism is mainly three-dimensional diffusion-controlled. Activation energy is 484 kJ/mol in isothermal transformation for Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass. These different results were discussed using kinetic models. In addition, average activation energy of Cu₄₆Zr₄₅Al₇Y₂ bulk metallic glass calculated using Arrhenius equation is larger than the value calculated by the Kissinger method in non-isothermal conditions. The reason lies in the nucleation determinant in the non-isothermal mode, since crystallization begins at low temperature. Moreover, both nucleation and growth are involved with the same significance during isothermal crystallization. Therefore, the energy barrier in isothermal annealing mode is higher than that of isochronal conditions.     

Influence of outphase Cu50Ti50 amorphous alloy addition on microstructural evolution of mechanically alloyed Zr66.7Ni33.3 amorphous alloy

The influence of outphase Cu₅₀Ti₅₀ amorphous alloy addition on microstructural evolution of Zr_66.7Ni_33.3 amorphous alloy has been investigated using a mechanical alloying method. It has been found that the milling induced microstructural evolution is related to the change of peak positions of the first maximum on X-ray diffraction patterns of the as-obtained amorphous alloys. With increasing milling time, the 3 wt.% Cu₅₀Ti₅₀ addition can give rise to the cyclic amorphization transformation of the as-milled alloy. The mechanical stability of the mixing amorphous phase can be greatly enhanced with increasing Cu₅₀Ti₅₀ addition up to 10 wt.%. Moreover, the addition of outphase Cu₅₀Ti₅₀ amorphous alloy not only increases the onset crystallization temperature of Zr_66.7Ni_33.3 amorphous alloy but also alters its crystallization mode. The effect of outphase amorphous addition on the mechanical stability of the Zr_66.7Ni_33.3 amorphous phase has been discussed based upon the bond order theory.     

Crystallization processes in amorphous Zr54Cu46 alloy

The crystallization of amorphous Zr₅₄Cu₄₆ alloy was investigated by using X-ray diffraction (XRD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) techniques. The experimental results show that an endothermic peak in DSC traces for amorphous Zr₅₄Cu₄₆ alloy exists at about 1006 K, indicating following eutectoid reaction occurs, namely, Cu₁₀Zr₇+CuZr₂↔CuZr in amorphous Zr₅₄Cu₄₆ alloy during heating. With increasing the heating rate, the glass transition temperature T_g and onset crystallization temperature T_x of amorphous Zr₅₄Cu₄₆ alloy increase in parallel, and the supercooled liquid region ΔT_x (=T_x−T_g) holds almost constant with an average value of 44 K. Both XRD and TEM results prove that Cu₁₀Zr₇ and CuZr₂ are main crystallization products for amorphous Zr₅₄Cu₄₆ alloy under continuous heating conditions. No CuZr phase is identified because of its small precipitation amount. Finally, the crystallization processes of amorphous Zr₅₄Cu₄₆ alloy were summarized.     

Non-isothermal crystallization kinetics of La2CaB10O19 from glass

The non-isothermal crystallization kinetics of La₂CaB₁₀O₁₉ (LCB) from a La₂O₃-CaO-B₂O₃ glass was studied. Differential thermal analysis methods were performed on three glass powders to obtain the kinetic parameters of LCB crystallization mechanism. The activation energies for overall crystallization (E), obtained by the methods of Kissinger and Ozawa, were in the range of 479-569 kJ/mol. Multiple (five) analysis methods were used to estimate the Avrami exponent (n), which could consequently be reduced into the single value of n = 3.1 ± 0.3. The growth morphology index (m) of LCB was corroborated by microscopy (optical and electron) images, which revealed a three dimensional growth. Energy dispersive spectroscopy confirmed that LCB is the crystallizing phase from the glass by an interface controlled mechanism. The parameters of the Johnson-Mehl-Avrami kinetic model for the analysis of LCB crystallization from glass were found to be n = m = 3.     

Considerations on the structure and physical properties of B2O3-SiO2 and GeO2-SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B₂O₃-SiO₂ and GeO_2-SiO₂ glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B₂O₃, GeO₂ and SiO₂. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO₃, GeO₄ and SiO₄ units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si-O-B or Si-O-Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B₂O₃ or GeO₂ in the concerned glasses.     

One-step fabrication of Fe2O3/Ag core-shell composite nanoparticles at low temperature

The Fe₂O₃/Ag core-shell composite nanoparticles were successfully prepared via a simple method at low temperature. X-ray diffraction data revealed the formation of core-shell composite nanoparticles, with Fe₂O₃ as the core and silver as the shell. The results from the transmission electron microscopy and scan electron microscopy further indicated that the composite nanoparticles were spherical with a core diameter and shell thickness of 26.0 nm and 13.5 nm, respectively. Magnetic measurements showed that the composite nanoparticles exhibited a typical ferromagnetic behavior, a specific saturation magnetization of 0.95 emu/g and an intrinsic coercivity of 104.0 Oe at room temperature. For a standard two-probe analysis at room temperature, the composite nanoparticles showed a typical conductive behavior and its conductivity was about 3.41 S/m. Moreover, this present synthesis method of Fe₂O₃/Ag core-shell composite nanoparticles shows an easy processing and does not need high-temperature calcining to attain the final product, which can be applied in a variety of areas, including catalysis, medicine, photonics, and new functional device assemblies.     

Structural and electrical properties of lead-free perovskite ceramic: Ba(In1/2Nb1/2)O3

Lead-free perovskite Ba(In_1/2Nb_1/2)O₃ was prepared by conventional ceramic fabrication technique at 1350 °C/5 h in air atmosphere. The crystal symmetry, space group and unit cell dimensions were determined from Rietveld analysis using FullProf software whereas crystallite size and lattice strain were estimated from Williamson-Hall approach. XRD analysis of the compound indicated the formation of a single-phase cubic structure with the space group Pm3m. EDAX and SEM studies were carried out in order to evaluate the quality and purity of the compound. Complex impedance as well as electric modulus analyses suggested the dielectric relaxation to be of non-Debye type. The correlated barrier hopping (CBH) model was employed to successfully explain the mechanism of charge transport in Ba(In_1/2Nb_1/2)O₃.     

The growth and structure of Pb3Ga2Ge4O14 and Ba3Ga2Ge4O14 single crystals

Conditions for the flux synthesis of Pb₃Ga₂Ge₄O₁₄ and Ba₃Ga₂Ge₄O₁₄ single crystals and their solid solutions Pb_{3 − x} Ba_xGa₂Ge₄O₁₄ are studied. Structural analysis showed that the Ga³⁺-and Ge⁴⁺-cation positions in flux-grown Pb₃Ga₂Ge₄O₁₄ and Ba₃Ga₂Ge₄O₁₄ single crystals are not mixed. __________ Translated from Kristallografiya, Vol. 49, No. 2, 2004, pp. 325–328. Original Russian Text Copyright ? 2004 by Bezmaternykh, Vasil’ev, Gudim, Temerov. This work was presented at the National Conference on Crystal Growth (NCCG-2002, Moscow).     

Fabrication of highly homogeneous As2Se3 glass under argon flow

The present study relates to a new method for the synthesis of As₂Se₃ glass in a controlled atmosphere. The advantage of this technique is that it does not require sealing of the silica reaction container and therefore makes it likely to substitute the current industrial batch by batch synthesis which actually needs very expensive single-use sealed silica vessels.An experimental device has been developed for these purposes. It is equipped with a stirring mechanism to homogenize the molten bath. In order to avoid contamination by oxygen and moisture, the synthesis is carried out under argon flow (pressure of 1 bar). Material losses during synthesis can be reduced to less than 2% when temperature is progressively increased up to 430 °C. Bulk glass ingots are finally obtained according to a two-step annealing process. Their chemical composition is analyzed by EDS and shows a variation range of less than 0.2%. The excellent reproducibility of the given method is also confirmed by the refractive indexes, that do not differ for more than 1 · 10⁻³ from one another.Adverse absorption bands due to oxygen do not occur in the 8-12 μm spectral region when 1000 ppm of Mg is added. As no distilling operation has been carried out until now, the magnesium oxide partially keeps staying in the glass and leads to scattering losses at short wavelengths.     

Flux growth and morphology analysis of Na3VO2B6O11 crystals

Colorless and transparent Na₃VO₂B₆O₁₁ (NVB) crystal has been grown by the top seeded solution growth method using NaVO₃ as the flux at cooling rates of 0.8–1.5 °C/day, in the temperature range 610–650 °C. A well-developed morphology of the crystals was observed and analyzed. The grown crystals were characterized by powder X-ray diffraction (PXRD), infrared spectroscopy and second harmonic generation (SHG) test.     

Microstructural changes in epitaxial YBa2Cu3O7−δ thin films due to creation of O vacancies

Structural and transport properties of YBa₂Cu₃O_7−δ thin films subjected to different heat treatments and, consequently, having different O vacancy contents are investigated. It is observed that lattice parameters of the films follow the trend of the bulk material, indicating that either the additional stresses created in c-axis oriented films by O vacancies are negligibly small or they are relaxed at elevated temperatures. In addition, heat treatment under relatively low O₂ partial pressures, used to create O vacancies, leads to considerable reduction in local variations of lattice spacings in YBa₂Cu₃O_7−δ thin films.     

Growth and optical characteristics of Ce-doped and Ce : Na-codoped BaLiF3 single crystals

Ce-doped and Ce : Na-codoped BaLiF₃ single crystals were grown by the Czochralski technique under reactive atmosphere. Na⁺-ions, used as a charge-compensating impurity, compete with Ce³⁺-ions for Ba²⁺ sites in the host, reducing the Ce³⁺ incorporation and degrading the mechanical integrity of crystals. Ce-doped BaLiF₃ showed potential for UV tunable lasers.     

Influence of simultaneous doping of Tl and Bi on microstructure and critical current density of HgBa2Ca2Cu3O8+δ

It has been found that simultaneous doping of Tl and Bi at Hg site of HgBa₂Ca₂Cu₃O_8+δ HTSC phase induces interesting microstructural variants in the form of long period polytypoid (LPP) like structure embodying native defect substructures. It has been observed that the as synthesized (HgTl_0.2−xBi_x)Ba₂Ca₂Cu₃O_8+δ (with x = 0.05, 0.10, 0.15) phases have superconducting onset transition temperature (T_c) of about ∼133 K. However, the intragrain critical current density (J_c) for the various materials with different compositions varies significantly. It varies from 6.2 × 10⁶ A/cm² to 2.9 × 10⁶ A/cm² at 5 K and 1 T for (HgTl_0.10Bi₁₀)Ba₂Ca₂Cu₃O_8+δ and (HgTl_0.15Bi_0.05)Ba₂Ca₂Cu₃O_8+δ HTSC phase respectively. A correlation between the intragrain J_c and the defect substructures has been found to be present. This correlation has been described and disscussed. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The investigation of the magnetic interaction between Cu2+ and V4+ ions in x(CuO·2V2O5)(1 − x)[2B2O3·K2O] glasses

EPR and magnetic susceptibility measurements have been performed on (CuO·2V₂O₅)(1?x)[2B₂O₃·K_2O] glasses with 0 ? x ? 40 mol. %.For x < 10 mol.%, both Cu²⁺ and V⁴⁺ ions are present mostly as the isolated species. The values of MO coefficients indicate a high covalent degree of the transition metal (TM)-oxygen bonds. Also, the EPR parameters suggest the presence of strong (TM)-oxygen bonds along the 0_z axis, which lead to an octahedral (Oh) symmetry component at TM ions sites.In the case of 10 ? x ? 40 mol.%, the dipole-dipole and superexchange interactions occur between transition metal ions, which determine a broad resonance line at $\text{g ? 2}$. The strong interactions between Cu²⁺ and V⁴⁺ ions give rise to the exchange coupled Cu²⁺ V⁴⁺ pairs in the studied glasses with x > 10 mol.% (y > 3.9 mol.%).     

Glass formation and crystallization behavior in Mg65Cu25Y10−xGdx (x=0, 5 and 10) alloys

The glass forming ability and crystallization behavior of Mg₆₅Cu₂₅Y_10−xGd_x (x=0, 5 and 10) alloys have been investigated. The glass forming ability (GFA) is significantly improved when Y in Mg₆₅Cu₂₅Y₁₀ is substituted with Gd. Ternary Mg₆₅Cu₂₅Gd₁₀ bulk metallic glass (BMG) with diameter of at least 8 mm was successfully fabricated by conventional Cu-mold casting method in air atmosphere. Mg₂(Y, Gd) is the first competing crystalline phase against the glass formation in the Mg₆₅Cu₂₅Y_10−xGd_x (x=0, 5) alloys, while Mg₂Cu and Cu₂Gd are the competing crystalline phases in the Mg₆₅Cu₂₅Gd₁₀ alloy. Therefore, the suppression of the formation of Mg₂(Y, Gd) during cooling from the liquid improves the GFA significantly.     

Glass-forming ability and crystallization of bulk metallic glass (HfxZr1−x)52.5Cu17.9Ni14.6Al10Ti5

We have produced a series of bulk metallic glasses of composition (Hf_xZr_1−x)_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ (with x=0-1) by an arc melting/suction casting method. The density of these alloys increases by nearly 67% with increasing Hf content from 6.65 g/cm³ (x=0) to 11.09 g/cm³ (x=1). Over the same composition range the glass-forming ability decreases, as demonstrated by the size of the largest amorphous ingots that can be cast without crystallization. Although both the glass transition temperature and the melting temperature increase linearly with increasing Hf content, the reduced glass transition temperature (T_g/T_m) decreases, from 0.64 (x=0) to 0.62 (x=1), which suggests that the `confusion principle' correlating increased glass-forming ability with increased number of components, does not apply in this case due to the chemical similarity between Zr and Hf. A different crystallization behavior is observed for Zr-based and Hf-based glasses. The final crystalline phases are CuZr₂ and Zr₂Ni for Zr-based alloys, and Al₁₆Hf₆Ni₇ and CuHf₂ for Hf-based alloys.     

Dielectric relaxation study of hydrogen exposure as a source of two-level systems in Al2O3

An important question in the manufacture of superconducting electronics is how to control the two-level systems found in amorphous insulators. The present article shows that hydrogen has a marked impact on the two-level systems in thin films of reactively sputtered Al₂O₃, a standard tunnel oxide for Josephson junctions. The magnitude of dielectric relaxation current in Al₂O₃ films, believed to be caused by two-level systems, is shown to increase monotonically with the flow rate of H₂ into the chamber during deposition. This points toward a potential need for controlling hydrogen during the manufacture of superconducting electronics utilizing Al₂O₃.