Spectroscopic characterisation of local structure in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses doped with gadolinium

Gadolinium doped bismuth borate glasses containing up to 30 mol% Y₂O₃ were prepared by fast melt quenching method. The effect of yttrium on the local order in 3B₂O₃ · Bi₂O₃ and B₂O₃ · Bi₂O₃ glass matrices, particularly on the bismuth sites, was investigated by infrared (IR) spectroscopy and electron paramagnetic resonance (EPR) of Gd³⁺ ions. The IR results show that the local structure is more ordered in the glass system with higher bismuth content and the progressive addition of yttrium increases the local disorder in both bismuth–borate glass matrices. The EPR results indicate that Gd³⁺ ions occupy both bismuth and yttrium sites and reflect the same structural disorder like that suggested by IR results.     

Variable—Range hopping in Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

The dc conductivity of the glasses in the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system was studied at temperatures between 223 and 393 K. At temperatures from 300 to 223 K, T^–1/4 (T is temperature) dependence of the conductivity was found, however, both Mott variable-range hopping and Greaves intermediate range hopping models are found to be applicable. Mott and Greaves parameters analysis gave the density of states at Fermi level N (E_F) = 3.13 × 10²⁰–21.01 × 10²⁰ and 1.93 × 10²¹–16.39 × 10²¹ cm^–3eV^–1 at 240 K, respectively. The variable-range hopping conduction occurred in the temperature range T = 300–223 K, since W_D was found to be large (W_D = 0.08–0.14 eV for these glasses) and dominated the conduction at T < 300 K.     

Mechanical and acid-etching properties of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZnO–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-containing ceramic fillers

The properties of the composite, having a complicated microstructure, are decided by many factors such as those of glass matrix, crystal phases, fillers, and holes. We investigated how the addition of ceramic fillers to the glass matrix affects the mechanical and etching properties of the glass composite by forming new crystal phases. Different amounts of two fillers, ZnO and Al₂O₃, were added to a glass frit consisting of Bi₂O₃–ZnO–B₂O₃. It was sintered at 550 °C for 30 min. Based on the results of this study, the porosity and degree of crystallization of the composites could be controlled by adjusting the content of the ZnO and Al₂O₃ fillers. Therefore, porosity and degree of crystallization formed by the reaction between a glass matrix and fillers influence the mechanical and etching properties of the composite.     

Structure and properties of CaF<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

FTIR spectroscopy has been employed to investigate the structure of CaF₂–B₂O₃ glasses. It is proposed that CaF₂ partially modifies the borate network forming \textCa _{1 / 2} ²⁺ [\textBO _{3 / 2} \textF] ^- {\text{Ca}}_{ 1 / 2}^{ 2+ } [{\text{BO}}_{ 3 / 2} {\text{F]}}^{ - } units. The rest of CaF₂ is assumed to build an amorphous network formed of CaF₄ tetrahedra. Analysis of density and molar volume revealed that the volume of CaF₄ tetrahedron in the studied glasses is slightly greater than that in the crystalline form. Data of density, molar volume, and electric conductivity have been correlated with the glass structure. As far as the authors know, CaF₂–B₂O₃ glasses are investigated for the first time.     

Optical properties and crystallization of glasses in the system Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi₂O₃–MoO₃–B₂O₃. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (E _opt) and changes in cut-off (λ_c) depending on composition are reported. It was established that the increase in the MoO₃ content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.     

FT-IR,Raman and UV–VIS spectroscopic studies of copper doped 3Bi<Subscript>2</Subscript>O<Subscript>3 </Subscript>·B<Subscript>2</Subscript>O<Subscript>3</Subscript> glass matix

FT-IR, Raman and UV–VIS experimental results were presented for xCuO·(100-x)[3Bi₂O₃·B₂O₃] glass system, where 0 ≤ x ≤ 50 mol%. The FT-IR measurements indicate the presence in xCuO·(100-x)[3Bi₂O₃·B₂O₃] glasses of BO₃, BO₄ units, BiO₃ pyramidal and distorted BiO₆ octahedral units and their dependence of CuO content. The Raman scattering data indicate that for 0 ≤ x ≤ 10 mol% the structure of studied glasses consist from BiO₃ pyramidal and distorted BiO₆ octahedral units, ring and chain type of metaborate groups, ortoborate and pyroborate groups. For higher concentration the Raman spectra suggest that the structure become more disordered. The FT-IR and Raman bands characteristic for CuO were not directly evidenced, but the absorption bands specific for the glass matrix are influenced by the presence of copper ions in the glass network structure. The optical absorption confirms the presence of Cu²⁺ in the CuO doped 3Bi₂O₃·B₂O₃ glass matrix.     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Effect of sintering temperatures on properties of BaO–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> glass/silica composites for CBGA package

BaO–B₂O₃–SiO₂–Al₂O₃ (BBSA) glass/silica composites synthesized by solid-state reaction method were developed for CBGA packages, and the effects of sintering temperature (900–950 °C) on the phase transformation, microstructure, thermal, mechanical and electrical properties were investigated. XRD results show that the major phases quartz and cristobalite, and the minor phase BaSi₂O₅ are detected in BBSA composites. Furthermore, it was found that the quartz phase transforms to cristobalite phase at 930–940 °C. The formation of cristobalite phase with higher coefficient of thermal expansion (CTE) led to the increase of CTE value of BBSA composites. However, excessive cristobalite phase content would degrade the mechanical properties and the linearity of thermal expansion of the ceramics. BBSA composites sintered at 920 °C exhibited excellent properties: low dielectric constant and loss (ε_r = 6.2, tanδ = 10^?4 at 1 MHz), high bending strength (179 MPa), high CTE (12.19 ppm/°C) as well as superior linearity of the thermal expansion.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Characterization and analysis of CaO–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript> ternary system ceramics

The dielectric, thermal and mechanical properties of CaO–SiO₂–B₂O₃ ternary system ceramics by solid-phase method have been carried out and quantitive analysis been examined by X-ray diffraction (XRD) patterns. The results showed that the major crystalline phase of CaO–SiO₂–B₂O₃ ternary system ceramics was wollastonite (about 90 wt%) which existed at the temperature ranging from 950 to 1,100 °C. It is also observed that wollastonite could be transformed to pseudowollastonite at 1,200 °C. In addition, with increase in calcination temperature, the amount of wollastonite increases. When the sintering temperature is at 1,100 °C, the amount of wollastonite has a maximum value of 92.7 wt%. Accordingly, CaO–SiO₂–B₂O₃ ternary system ceramics achieved excellent properties at 1,100 °C, such as dielectric constant of 8.38, dielectric loss of 1.51 × 10⁻³ at 1 MHz, linear thermal-expansion coefficient (300 K) of 6.68 × 10⁻⁶/K, bending strength of 121.75 Mpa. Analysis of the mechanical and dielectric properties showed that the measured bending strength, dielectric constant and loss of CaO–SiO₂–B₂O₃ ternary system ceramics can be substantially modified and improved by controlling the sintering temperature, in particular due to the amount of wollastonite crystalline phase and size of grains.     

Phase formation and magnetic property evolution processes of the hexaferrite with composition BaO⋅0.9Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>⋅5.1Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>

The phase formation and magnetic property evolution processes of the hexaferrite with composition BaO?0.9Sc₂O₃?5.1Fe₂O₃ have been investigated. Results show that when the calcination temperature is lower than 1000 °C, the spinel phase BaFe₂O₄ and M-type hexaferrite phase BaFe₁₂O₁₉ dominate. The M-type hexaferrite BaFe_12?xSc_xO₁₉ (0?<?x?≤?1.8) appears above 1050 °C and becomes a single phase BaFe_10.2Sc_1.8O₁₉ above 1200 °C. A two-step decrease of both the coercivity and remanence ratio is observed above 1050 °C, which agrees well with the appearance of soft magnetic phase BaFe_12?xSc_xO₁₉ (0?<?x?≤?1.8). The saturation magnetization of the sample increases with calcination temperature until 1100 °C and then decreases. Raman spectra results show that the above magnetic property evolutions can be explained by a temperature dependent incorporation of Sc³⁺ into the lattice sites nearby the magnetic blocks’ interfaces. This weakens the local magnetic exchange interactions between Fe³⁺ and thus leads to a change in the magnetic structure.     

Catalytic combustion of methane over Pt and PdO-supported CeO<Subscript>2</Subscript>–ZrO<Subscript>2</Subscript>–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

Catalytic combustion of methane was investigated on Pt and PdO-supported CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts prepared by a wet impregnation method in the presence of polyvinylpyrrolidone. The catalysts were characterized by X-ray fluorescence analysis, X-ray powder diffraction, X-ray photoelectron spectra, transmission electron microscopy, and BET specific surface area measurements. The Pt/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ and PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were selective for the total oxidation of methane into carbon dioxide and steam, and no by-products such as HCHO, CO, and H₂ were obtained. The catalytic activities of the PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalysts were relatively higher than those of the Pt-supported catalysts, due to the facile re-oxidation of metallic Pd into PdO based on lattice oxygen supplied from the CeO₂–ZrO₂–Bi₂O₃ bulk. A decrease in the calcination temperature during the preparation process was found to be effective in enhancing the specific surface area of the catalysts, whereby particle agglomeration was inhibited. Optimization of the PdO amount and calcination temperature enabled complete oxidation of methane at temperatures as low as 320 °C on the 11.6 wt% PdO/CeO₂–ZrO₂–Bi₂O₃/γ-Al₂O₃ catalyst prepared at 400 °C.     

Synthesis of thorn-like Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>·H<Subscript>2</Subscript>O by hydrothermal method

Thorn-like polycrystalline Ca₂B₂O₅·H₂O microspheres with nano-sized slices were synthesized using boric acid and calcium hydroxide as reactants by a facile catalyst-free hydrothermal method at low temperature. The products were characterized by means of X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern reveals that the Ca₂B₂O₅·H₂O is a monoclinic phase polycrystalline with cell parameters a = 0·6702, b = 0·5419 and c = 0·3558 nm. SEM also reveals that the monoclinic phase polycrystalline are thorn-like microspheres composed of many flakes with an average thickness of <100 nm. Possible reaction and growth mechanism were also discussed.     

Fabrication of Yb<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–SiO<Subscript>2</Subscript> Optical Fibers with a Perfect Step-Index Profile by the MCVD Process

An all-vapor phase MCVD process has been proposed for the fabrication of fiber preforms with a Yb₂O₃–Al₂O₃–P₂O₅–SiO₂ multicomponent glass core. We have investigated the tubular preform collapse into a rod and demonstrated approaches capable of preventing P₂O₅ losses in the central part of the core during the collapse process. Preforms with a flat, perfect step-index profile have been fabricated.     

Crystallization and microstructural evolution of MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript>–La<Subscript>2</Subscript>O<Subscript>3</Subscript> glass-ceramics

Crystallization and microstructure of glasses with the molar compositions 1MgO·1.2Al₂O₃·2.8SiO₂·1.2TiO₂·xLa₂O₃ (x = 0.1 and 0.4) were thermally treated at different temperatures in the range from 950 to 1250 °C and then analyzed by X-ray diffraction and scanning electron microscopy, in combination with energy-dispersive X-ray spectroscopy and electron backscatter diffraction. It was found that the microstructure is first homogeneous with the precipitation of randomly distributed crystals and then indialite domains with embedded perrierite and rutile crystals are formed. For higher temperatures or prolonged times, more domains appear and expand into the bulk of the sample. Finally, the entire sample consists of the indialite domains and the boundaries that are enriched in rutile, perrierite, and magnesium aluminotitanate. Nevertheless, very distinct differences are observed between the samples with different La₂O₃ concentrations. For the sample with x = 0.4, the domains were detected at lower temperatures, while the quantity and size of the domains increase faster due to the promoted precipitation of indialite. For the sample with x = 0.1, in addition to the domain boundaries, secondary boundaries between the “regions” (assemblages of the domains) are observed in a larger length scale. The average size of the crystalline phases found between the “regions” is larger than that typically observed at the domain boundaries. The sizes of the crystals at the boundaries decrease with higher concentrations of La₂O₃, and the crystals (especially perrierite) within the domains become larger, resulting in a more homogeneous microstructure. This results in better dielectric properties, i.e., much higher quality factor for the sample with x = 0.4 in comparison to that with x = 0.1 after heat-treatment at 1150 or 1250 °C.     

The crystallographic orientation relationship between Al<Subscript>2</Subscript>O<Subscript>3</Subscript> and MgAl<Subscript>2</Subscript>O<Subscript>4</Subscript> in the composite material Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al–Mg–Si alloy

The formation mechanism of spinels on Al₂O₃ particles in the Al₂O₃/Al–1.0 mass% Mg₂Si alloy composite material has been investigated by transmission electron microscopy (TEM) in order to determine the crystallographic orientation relationship. A thin sample of the Al₂O₃/Al–Mg–Si alloy composite material was obtained by the FIB method, and the orientation relationship between Al₂O₃ and MgAl₂O₄, which was formed on the surface of Al₂O₃ particles, was discovered by the TEM technique as follows:

Phase equilibria in the La<Subscript>2</Subscript>O<Subscript>3</Subscript>-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>-CoO system at 1100°C

The phase equilibria in the La₂O₃-Ga₂O₃-CoO system have been studied at 1100°C in air, using samples prepared by a standard ceramic processing technique from oxides and by a glycine-nitrate combustion process. The composition ranges and structures of solid solutions in this system have been determined by x-ray powder diffraction: LaGa_1?x Co _x O₃ (0 < x ≤ 0.05), LaCo_1?x Ga _x O₃ (0 < x ≤ 0.10), La₄Ga_2?x Co _x O₉ (0 < x ≤ 0.20), Co_1?x Ga_2+x O₄ (?0.20 ≤ x ≤ 0.05). The unit-cell parameters of the solid solutions vary little with composition, in accordance with the small difference in ionic radius between gallium and cobalt. The 1100°C section through the phase diagram of the La₂O₃-Ga₂O₃-CoO system in air is presented.     

Microstructure,interfaces and creep behaviour of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) eutectic ceramic composites

New compositions in the melt-grown eutectic ceramics field are investigated for thermomechanical applications. This paper is focused on the Al₂O₃–Sm₂O₃–(ZrO₂) system. The studied compositions give rise to interconnected microstructures without anisotropy along the growth direction. At variance with the binary eutectic Al₂O₃–SmAlO₃, the homogeneity of the microstructure of the Al₂O₃–SmAlO₃–ZrO₂ ternary eutectic is less sensitive to the growth rate. Interfaces between the alumina and perovskite phases are investigated by high-resolution transmission electron microscopy (TEM). They are semi-coherent. In stepped interfaces, the facets are parallel to dense planes of each phase. The steps have a dislocation character and may accommodate both misfits. The ternary eutectic displays a very good creep behaviour with strain rates very close to those obtained on other previously studied eutectics in the Al₂O₃–RE₂O₃(RE = Y, Gd, Er)–ZrO₂ systems. The deformation micromechanisms are analysed by TEM in the three eutectic phases. After creep, dislocations are present in every phase. The activation of unusual slip systems (pyramidal slip in the alumina phase) shows that high local stresses can be reached. The presence of dislocation networks with low energy configurations is consistent with predominance of dislocation climb processes controlled by bulk diffusion.     

Influence of Bi substitution on microwave dielectric properties of BaO–La<Subscript>2</Subscript>O<Subscript>3</Subscript>–Sm<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript> ceramics

The influences of Bi substitution on microwave dielectric properties of Ba₄(La_0.5Sm_0.5)_9.33Ti₁₈O₅₄ solid solutions were investigated. Dielectric ceramics with general formula Ba₄(La_(0.5−z)Sm_0.5Bi _z )_9.33Ti₁₈O₅₄, z = 0.0–0.2 were prepared by conventional solid state route. The structural analysis of all the samples was carried out by X-ray diffraction and scanning electron microscopy. The dielectric properties were investigated as a function of Bi contents using open-ended coaxial probe method in the frequency range 0.3–3.0 GHz at room temperature. Dielectric constant varies from 83 to 88 and loss tangent from 2.1 × 10⁻³ to 5.5 × 10⁻³ at 3 GHz with temperature coefficient of resonant frequency changing from 106.7 to −8.4 ppm/oC as Bi contents increases from z = 0.00–0.20. It has been found that dielectric constant and temperature coefficient of resonant frequency improve whereas loss tangent is adversely affected with increase in Bi substitution.