Preparation,characterization, and mechanical-optical properties of telluro-borate glasses containing tungsten

The current work is interested in the preparation, characterization, and mechanical-optical properties of the glasses in the (75-x)B₂O₃–10SrO–8TeO₂–7ZnO−xWO₃ system, with (x = 0 (BSTZW0), 1 (BSTZW1), 5 (BSTZW2), 10 (BSTZW3), 22 (BSTZW4), 27 (BSTZW5), 34 (BSTZW6), and 40 mol% (BSTZW7). The preparation of the glasses has involved the melt-quenching route. The new glasses are characterized by different characterization techniques using densimeter, microhardness, Raman spectroscopy, UV–visible absorption and emission, and X-ray diffraction. Photoluminescence can determine the impact of substituting B₂O₃ with WO₃ on the mechanical-optical parameters and the structure of the present glasses. The prepared samples’ X-ray patterns showed amorphous states. The density value rises from 2.88 to 4.50 g/cm3, with the amount of WO₃ rising from 0 to 40 mol% as a result of the difference in molecular weight between WO₃ and B₂O₃. The Vickers microhardness (Hv) rises as the amount of WO₃ increases as a result of a decrease in free volume and the formation of covalent bonds. The elastic moduli were found to increase when the WO₃ concentrations increased from 0 to 40 mol%. This increase depends on the formation of bridging oxygen atoms. The Raman bands are designed to correspond to the bonds that form the structure of the current glass and detect the insertion of WO₃ content by the attribution of the new W–O–W and W–O bonds. The UV–Visible spectroscopy analysis showed no band characteristic for the reduced species of W⁵⁺ ions identified by dark blue. However, the photoluminescence spectra showed emission bands (under excitation at 300 nm) that are associated with the active centers of W⁴⁺, W⁵⁺, and W⁶⁺ ions.     

Environmental influence of high Na2O additions on microstructure and ligand field parameters of Cr3+ inside borosilicate glass

A glass system based on the Na₂O/B₂O₃-doped CrO₃ borosilicate has been prepared by the melt quenching technique. The structure, color, optical absorbance and ligand field parameters were investigated for a wide range of Na₂O additives (20–60 mol%). All X-ray photoelectron spectroscopy (XPS) profiles were used to study the chemical shift states of the glass-constituting elements. Fourier transform infrared (FTIR) analyses explored the internal structure and subnetwork units. Furthermore, from the FTIR results, we concluded the transformation of trigonal borate units (BO₃) to tetrahedral borate units (BO₄) and the possibility of transformation from B₃-O-Si linkages to B₄-O-Si linkages. Despite the fixed CrO₃ content, the doped glasses showed a color transition from green to yellow with additional Na₂O content. The increased intensity of the band at 451–427 nm and the decreased intensity of the band at 619–627 nm are the main reasons for this color transformation. The optical absorption spectra confirmed the existence of Cr³⁺ and Cr⁶⁺ states. A decreasing behavior for the crystal field splitting (10Dq) and an increasing behavior for Racah parameter (B) were obtained with further Na₂O additives. The decreasing behavior of 10Dq was attributed to reduced oxygen concentrations with more Na₂O/B₂O₃ substitutions. The increasing behavior of B reflects the tendency of the bond between the Cr cations and their oxygen ligands towards an ionic nature. Moreover, the Dq/B values indicated that Cr³⁺ cations are in high-field positions for the glass sample containing 20 mol% Na₂O, and Cr³⁺ cations are in intermediate field positions for the glass sample containing 30 mol% Na₂O. However, for the glass samples doped with 40, 50 and 60 mol% Na₂O glass samples, Cr³⁺-cations are in weak field positions. These results of (Dq/B) recommend the glass sample doped with 20 mol% Na₂O for tunable laser applications.     

Dielectric polarizability of SiO2 in niobiosilicate glasses

Understanding the mechanisms contributing to dielectric properties of glasses is critical for designing new compositions for microwave frequency applications. In this work, dielectric permittivity was measured using a cavity perturbation technique at 10 GHz for a series of niobiosilicate glasses with the compositions (100-2x)SiO₂- xNb₂O₅- xLi₂O where x = 32.5, 30, 25, and 15 mol%. Permittivity measurements and glass compositions were used to calculate the polarizability of each cation-anion unit in the glass network using the Clausius-Mossotti equation. The SiO₂ polarizability in niobiosilicates was calculated to be 6.16 ų, which is much higher than the SiO₂ polarizability in fused silica glass (5.25 ų), alkali modified silicates (5.37 ų), and aluminosilicates (5.89 ų). The increasing trend in SiO₂ polarizability is attributed to the disruption in the connectivity of the SiO₄ tetrahedral network as it accommodates different network formers. The high SiO₂ polarizability of 6.16 ų accurately predicts measured dielectric permittivity when Nb₂O₅ = 25, 30, and 32.5 mol%, but overpredicts measured permittivity when Nb₂O₅ ≤ 15 mol%, which is attributed to a decrease in SiO₂ polarizability as the percentage of corner sharing SiO₄ tetrahedra with NbO₆ octahedra goes down. This work demonstrates that SiO₂ polarizability depends on chemistry and connectivity of the glass, which has important implications in designing glass compositions for microwave frequency applications.     

Influence of Al2O3/SiO2 ratio in multicomponent LNAS glasses and glass-ceramics on the crystallization behavior,microstructure and mechanical performance

Transparent glass-ceramics containing eucryptite and nepheline crystalline phases were prepared from alkali (Li, Na) aluminosilicate glasses with various mole substitutions of Al₂O₃ for SiO₂. The relationships between glass network structure and crystallization behavior of Li₂O–Na₂O–Al₂O₃–SiO₂ (LNAS) glasses were investigated. It was found that the crystallization of the eucryptite and nepheline in LNAS glasses significantly depended on the concentration of Al₂O₃. LNAS glasses with the addition of Al₂O₃ from 16 to 18 mol% exhibited increasing Q⁴ (mAl) structural units confirmed by NMR and Raman spectroscopy, which promoted the formation of eucryptite and nepheline crystalline phases. With the Al₂O₃ content increasing to 19–20 mol%, the formation of highly disordered (Li, Na)₃PO₄ phase which can serve as nucleation sites was inhibited and the crystallization mechanism of glass became surface crystallization. Glass-ceramics containing 18 mol% Al₂O₃ showed high transparency ～84% at 550 nm. Moreover, the microhardness, elastic modulus and fracture toughness are 8.56 GPa, 95.7 GPa and 0.78 MPa m^1/2 respectively. The transparent glass-ceramics with good mechanical properties show high potential in the applications of protective cover of displays.     

Improvement on the phase stability,mechanical properties and thermal insulation of Y2O3-stabilized ZrO2 by Gd2O3 and Yb2O3 co-doping

Gd₂O₃ and Yb₂O₃ co-doped 3.5 mol% Y₂O₃–ZrO₂ and conventional 3.5 mol% Y₂O₃–ZrO₂ (YSZ) powders were synthesized by solid state reaction. The objective of this study was to improve the phase stability, mechanical properties and thermal insulation of YSZ. After heat treatment at 1500 °C for 10 h, 1 mol% Gd₂O₃–1 mol% Yb₂O₃ co-doped YSZ (1Gd1Yb-YSZ) had higher resistance to destabilization of metastable tetragonal phase than YSZ. The hardness of 5 mol% Gd₂O₃–1 mol% Yb₂O₃ co-doped YSZ (5Gd1Yb-YSZ) was higher than that of YSZ. Compared with YSZ, 1Gd1Yb-YSZ and 5Gd1Yb-YSZ exhibited lower thermal conductivity and shorter phonon mean free path. At 1300 °C, the thermal conductivity of 5Gd1Yb-YSZ was 1.23 W/m K, nearly 25% lower than that of YSZ (1.62 W/m K). Gd₂O₃ and Yb₂O₃ co-doped YSZ can be explored as a candidate material for thermal barrier coating applications.     

Eu3+‐Activated Borogermanate Scintillating Glass with a High Gd2O3 Content

Eu³⁺‐activated borogermanate scintillating glasses with compositions of 25B₂O₃–40GeO₂–25Gd₂O₃–(10?x)La₂O₃–xEu₂O₃ were prepared by melt‐quenching method. Their optical properties were studied by transmittance, photoluminescence, Fourier transform infrared (FTIR), Raman and X‐ray excited luminescence (XEL) spectra in detail. The results suggest that the role of Gd₂O₃ is of significance for designing dense glass. Furthermore, energy‐transfer efficiency from Gd³⁺ to Eu³⁺ ions can be near 100% when the content of Eu₂O₃ exceeds x = 4, the corresponding critical distance for Gd³⁺–Eu³⁺ ion pairs is estimated to be 4.57 Å. The strongest emission intensities of Eu³⁺ ions under both 276 and 394 nm excitation are simultaneously at the content of 8 mol% Eu₂O₃. The degree of Eu–O covalency and the local environment of Eu³⁺ ions are evaluated by the value of Ω_t parameters from Judd–Ofelt analysis. The calculated results imply that the covalency of Eu–O bond increases with the increasing concentration of Eu³⁺ ions in the investigated borogermanate glass. As a potential scintillating application, the strongest XEL intensity under X‐ray excitation is found to be in the case of 6 mol% Eu₂O₃, which is slightly different from the photoluminescence results. The possible reason may be attributed to the discrepancy of the excitation mechanism between the ultraviolet and X‐ray energy.     

Mullite interaction with bismuth oxide from minerals and sol–gel processes

Mullite compounds with bismuth oxide in the SiO₂–Al₂O₃–Bi₂O₃ ternary system were synthesized from TEOS (C₂H₅O)₄Si, aluminum nitrate Al(NO₃)₃·9H₂O and bismuth nitrate Bi(NO₃)₃. Thermal and structural transformations were studied at temperatures ranging from 1000 to 1400 °C. The coexistence of Al₄Bi₂O₉ and Bi₄Si₃O₁₂ phases at temperatures up to 1000 °C was observed in compositions containing 5–31 mol% Bi₂O₃. Mullite is observed at temperature higher than 1000 °C in composition not exceeding 5 mol% of Bi₂O₃. Corundum coexist with a liquid above 1000 °C in all compositions containing more than 5 mol% Bi₂O₃. The liquid temperature is slightly above 1000 °C for all compositions. A tentative pseudo-binary diagram mullite-Bi₂O₃ is proposed. A similar system was studied with silico-aluminate compositions containing kaolinite and muscovite minerals. The occurrence of a liquid when Bi₂O₃ is added highly favors the mullite growth at temperature below 1200 °C. It is favored by local concentrations at interfaces of a transient liquid phase, which enhance the mobility of species.     

Synthesis and microstructure of Gd2O3-doped HfO2 ceramics

The effect of Gd₂O₃-doping on the crystal structure, surface morphology and chemical composition of the Gd₂O₃–HfO₂ system is reported. Gd₂O₃–HfO₂ ceramics with variable composition were prepared by varying the Gd₂O₃ composition in the range of 0–38 mol% balanced HfO₂. X-ray diffraction (XRD) analysis indicates that the Gd₂O₃ concentration influences the crystal structure of the Gd₂O₃–HfO₂ ceramics. Pure HfO₂ and Gd₂O₃ crystallize in monoclinic and body centered cubic structure, respectively. The Gd₂O₃–HfO₂ ceramics exhibit mixed monoclinic and fluorite structure when the Gd₂O₃ concentration is varied from 4 to 12 mol%. At 20 mol% of Gd₂O₃, existence of only the fluorite phase was found. Increasing the Gd₂O₃ concentration to 38 mol% results in the formation of single-phase pyrochlore Gd₂Hf₂O₇ (a = 5.258 Å).     

Microwave dielectric properties of CaWO4–Li2TiO3 ceramics added with LBSCA glass for LTCC applications

In this work, 0.86CaWO₄–0.14Li₂TiO₃ ceramics were prepared via a traditional solid-state process. The effects of Li₂O–B₂O₃–SiO₂–CaO–Al₂O₃ (LBSCA) addition on the phase formation, sintering character, microstructure and microwave dielectric properties of the ceramics were investigated. A small amount of LBSCA addition could effectively lower the sintering temperature of the ceramics. X-ray diffraction analysis revealed that CaWO₄ and Li₂TiO₃ phases coexisted without producing any other crystal phases in the sintered ceramics. The dielectric constant and Qf values were related to the amount of LBSCA addition and sintering temperatures. All specimens could obtain near-zero temperature coefficient (τ_f) values through the compensation of the positive τ_f of Li₂TiO₃ and the negative τ_f of CaWO₄. The 0.86CaWO₄–0.14Li₂TiO₃ ceramic with 0.5 wt% LBSCA addition and sintered at 900 °C for 3 h exhibited excellent microwave dielectric properties of ε_r=12.43, Qf=76,000 GHz and τ_f=−2.9 ppm/°C.     

Fabrication of double-cladding Ho3+/Tm3+ co-doped Bi2O3–GeO2–Ga2O3–BaF2 glass fiber and its performance in a 2.0-μm laser

A novel double-cladding Ho³⁺/Tm³⁺ co-doped Bi₂O₃–GeO₂–Ga₂O₃–BaF₂ glass fiber, which can be applied to a 2.0-μm infrared laser, was fabricated by a rod-tube drawing method. The thermal properties of the glass were studied by differential scanning calorimetry. It showed good thermal stability and matching thermal expansion coefficient for fiber drawing when T_x−T_g > 193°C and the maximum difference of the thermal expansion coefficient is 3.55 × 10⁻⁶/°C or less. The 2.0-μm luminescence characteristics were studied using the central wavelength of 808 nm pump light excitation. The results show that when the concentration ratio of Ho³⁺/Tm³⁺ reaches 0.5 mol%:1.0 mol%, the maximum fluorescence intensity was obtained in the core glass, the emission cross section reached 10.09 × 10⁻²¹ cm², and the maximum phonon energy was 751 cm⁻¹. In this paper, a continuous laser output with a maximum power of 0.986 W and a wavelength of 2030 nm was obtained using an erbium-doped fiber laser as a pump source in a 0.5 m long Ho³⁺/Tm³⁺ co-doped glass fiber. In short, the results show that Ho³⁺/Tm³⁺ co-doped 36Bi₂O₃–30GeO₂–15Ga₂O₃–10BaF₂–9Na₂O glass fiber has excellent laser properties, and it is an ideal mid-infrared fiber material for a 2.0-μm fiber laser with excellent characteristics     

Phosphoric acid-modified magnesium oxychloride: Study of water stability,kinetics, and pair distribution function

Magnesium oxychloride (MOC) excels in performance applications due to inherent structural strength, fire retardant properties, and numerous other attributes. To avoid the slow degradation of MOC when exposed to water, phosphoric acid is usually added, effectively increasing retention of structural properties (water stability). While this is an effective method, it is poorly understood. Additions of 2.5 wt.% and above had positive impacts on the water stability, preserving ~50 wt.% crystalline MOC after water stability tests. Phosphoric acid addition also impacted the reaction kinetics, increasing the activation energy of curing from 72.2 to 87.6-95.2 kJ/mol. Using synchrotron X-ray scattering and pair distribution function analysis, we identified an unreported amorphous phase formed when phosphoric acid is added; this phase contains structural motifs related to MgHPO₄·3H₂O (newberyte), Mg₂P₂O₇·3.5H₂O (magnesium pyrophosphate), and amorphous MOC phase. The short-range order of the samples show a prominent peak at ~3.2 Å that grows with increasing acid addition, believed to be a combination of newberyte (~3.4 Å Mg–P), pyrophosphate (~3.25 Å Mg–P), and MOC (~3.15 Å Mg–Mg). We propose that the increased water stability observed is due to this combined amorphous phase, which retains the low water solubility properties of MgHPO₄·3H₂O and Mg₂P₂O₇·3.5H₂O, effectively protecting the MOC crystalline phase.     

Borate melt structure: Temperature‐dependent B–O bond lengths and coordination numbers from high‐energy X‐ray diffraction

Borate melts containing <20 mol% Na₂O have been studied using high‐energy synchrotron X‐ray diffraction. Temperature dependencies of the mean B–O bond lengths are shown to vary strongly with soda content, by comparison to previous measurements on liquid B₂O₃ and Na₂B₄O₇. Whereas in liquid B₂O₃ linear thermal expansion of the BØ₃ units is observed, with coefficient α_BO = 3.7(2) × 10^?6 K^?1, this expansion is apparently slightly suppressed in melts containing <20 mol% Na₂O, and is dramatically reversed at the diborate composition. These effects are interpreted in terms of changes in the mean B–O coordination number, where the reaction BØ₄^? + BØ₃ ? BØ₃ + BØ₂O^? shifts to the right with increasing temperature. The empirical bond‐valence relationship is used to convert measured bond lengths, r_BO, to coordination numbers, n_BO, including a correction for the expected thermal expansion. This method is more accurate and precise than direct determination of n_BO from peak areas in the radial distribution functions. Gradients of Δn_BO/ΔT = ?3.4(3) × 10^?4 K^?1 close to the diborate composition, and Δn_BO/ΔT = ?0.3(1) × 10^?4 K^?1 for a 13(3) mol% Na₂O melt are observed, in reasonable agreement with Raman spectroscopic observations and thermodynamic modeling, with some quantitative differences. These observations go toward explaining isothermal viscosity maxima and changes in fragility across the sodium borate system.     

Role of MgO in lowering glass transition temperature and increasing hardness of lithium silicate glass and glass-ceramics

The effect of variation of MgO (1.5, 4.5 and 7.5 mol%) content on glass structure, crystallization behavior, microstructure and mechanical properties in a Li₂O–K₂O–Na₂O–CaO–MgO–ZrO₂–Al₂O₃–P₂O₅–SiO₂ glass system has been reported here. Increased amount of MgO enhanced the participation of Al₂O₃ as a glass network former along with [SiO₄] tetrahedra, reducing the amount of non-bridging oxygen (NBO) and increasing bridging oxygen (BO) amount in glass. The increased BO in glass resulted in a polymerized glass structure which suppressed the crystallization and subsequently increased the crystallization temperature, bulk density, nano hardness, elastic modulus in the glasses as well as the corresponding glass-ceramics. MgO addition caused phase separation in higher MgO (7.5 mol%) containing glass system which resulted in larger crystals. The nano hardness (～10 GPa) and elastic modulus (～127 GPa) values were found to be on a much higher side in 7.5 mol% MgO containing glass-ceramics as compared to lower MgO containing glass-ceramics.     

Dy3+ doped LiCl–CaO–Bi2O3–B2O3 glasses for WLED applications

Dy³⁺ doped calcium bismuth borate glasses were synthesized in the composition range of xLiCl-(30 − x)CaO-20Bi₂O₃-50B₂O₃ + 1 mol% Dy₂O₃ (x = 0, 2, 5, 7, 10 and 15 mol%, LC0, LC2, LC5, LC7, LC10 and LC15 respectively) using conventional melt-quench technique. Broad XRD profiles confirmed non-crystalline nature of synthesized compositions. The compositional dependencies of structural changes (using FTIR spectra), thermal behavior (using DSC thermographs) and optical band gap (using UV–Vis–NIR spectra) were discussed. Photoluminescence (PL) excitation spectra recorded at 577 nm yielded six different excitation peaks belonging to Dy³⁺ ions. The PL emission spectra recorded at 451 nm were analyzed to extract different light emission parameters viz. Y/B ratio, color coordinates, correlated color temperature (CCT) following CIE 1931 chromaticity diagram. The emission colors were found to lie in white light region and lies very close to standard white light emission. The CCT of sample LC10 (5335 K) is closest to CCT of standard white light (5615 K) which depicted the optimized concentration of LiCl for application of these glasses in WLED application.     

Solid Solution Effects on the Thermal Properties in the MgAl2O4–MgGa2O4 System

Solid solution effects on thermal conductivity within the MgO–Al₂O₃–Ga₂O₃ system were studied. Samples with systematically varied additions of MgGa₂O₄–MgAl₂O₄ were prepared and the laser flash technique was used to determine thermal diffusivity at temperatures between 200°C and 1300°C. Heat capacity as a function of temperature from room temperature to 800°C was also determined using differential scanning calorimetry (DSC). Solid solution in the MgAl₂O₄–MgGa₂O₄ system decreases the thermal conductivity up to 1000°C. At 200°C thermal conductivity decreased 24% with a 5 mol% addition of MgGa₂O₄ to the system. At 1000°C, the thermal conductivity decreased 13% with a 5 mol% addition. Steady‐state calculations showed a 12.5% decrease in heat flux with 5 mol% MgGa₂O₄ considered across a 12 inch thickness.     

Probing the Local Structure and Phase Transitions of Bi4V2O11‐Based Fast Ionic Conductors by Combined Raman and XRD Studies

In this article, we report the structural phase transitions in Bi₄V₂O₁₁ as observed from temperature‐dependent Raman scattering and X‐ray diffraction measurements. Four different types of highly disordered coordination polyhedra around the vanadium atoms with large dispersion of V–O bond lengths are observed in Bi₄V₂O₁₁ at ambient temperature. The observed V–O bond lengths could be grouped into two categories, viz. shorter <1.7 Å and longer >1.7 Å. The Raman modes of Bi₄V₂O₁₁ could be assigned to vibration of these bonds and V–O–V linkages. We could correlate the difference in degree of anharmonicity of the phonon modes with temperature to differences in V–O bond strength. The local structure of vanadium–oxygen network in Bi₄V_1.8Cu_0.2O_10.7 was also obtained by similar studies. The effect of highly disordered anion sublattice in the doped compound is reflected in the broadening of the Raman modes.     

Microstructure evolution of Si3N4 ceramics with high thermal conductivity by using Y2O3 and MgSiN2 as sintering additives

Silicon nitride (Si₃N₄) ceramics were prepared by gas-pressure sintering using Y₂O₃–MgSiN₂ as a sintering additive. The densification behavior, phase transition, and microstructure evolution were investigated in detail, and the relevance between the microstructure and the performance (including thermal conductivity and mechanical properties) was further discussed. A significant change from a bimodal to a homogeneous microstructure and a decreased grain size occurred with increasing Y₂O₃–MgSiN₂ content. When the small quantity of preformed β-Si₃N₄ nuclei grew preferentially and rapidly in a short time, an obvious bimodal microstructure was obtained in the sample with 4 mol% and 6 mol% Y₂O₃–MgSiN₂. When more β-Si₃N₄ nuclei grew at a relatively rapid rate, the sample with 8 mol% Y₂O₃–MgSiN₂ showed a microstructure consisting of numerous abnormally grown β-Si₃N₄ grains and small grains. When more β-Si₃N₄ nuclei grew simultaneously and slowly, there was a homogeneous microstructure and smaller grains in the sample containing 10 mol% Y₂O₃–MgSiN₂. Benefitting from the completely dense, significant bimodal microstructure, low grain boundary phase, and excellent Si₃N₄–Si₃N₄ contiguity, the sample containing 6 mol% Y₂O₃–MgSiN₂ exhibited great comprehensive performance, with a maximum thermal conductivity and fracture toughness of 84.1 W/(m⋅K) and 8.97 MPa m^1/2, as well as a flexural strength of 880.2 MPa.     

Crystallization of LiNbO3 and NaNbO3 in niobiosilicate glass–ceramics

Although glass–ceramics have been widely explored for their thermal stability and mechanical properties, they also offer unique symmetry-dependent properties such as piezoelectricity and pyroelectricity through controlled crystallization of a polar phase. This work examines crystallization of LiNbO₃ in a 35SiO₂–30Nb₂O₅–35Li₂O mol% composition and crystallization of LiNbO₃ and NaNbO₃ in a 35SiO₂–30Nb₂O₅–25Li₂O–10Na₂O mol% composition. Crystallization kinetics are examined using the Johnson–Mehl–Avrami–Kolmogorov (JMAK) theory where the Avrami exponent, n, is calculated to be 1.0–1.5. Microscopical analysis shows dendritic morphology, which when combined with the JMAK analysis, suggests diffusion-controlled one-dimensional growth. Adding Na₂O to the glass composition increases the inter-diffusivity of ions which causes LiNbO₃ to crystallize faster and lowers the activation energy of transformation from 1054 ± 217 kJ/mol in the ternary composition to 882 ± 212 kJ/mol. Time-temperature-transformation diagrams are presented which show that the temperature for maximum rate of transformation for LiNbO₃ is ∼650°C and for NaNbO₃ is ∼715°C.     

Effect of Al2O3 content on BaO–Al2O3–B2O3–SiO2 glass sealant for solid oxide fuel cell

The glass structure, wetting behavior and crystallization of BaO–Al₂O₃–B₂O₃–SiO₂ system glass containing 2–10 mol% Al₂O₃ were investigated. The introduction of Al₂O₃ caused the conversion of [BO₃] units and [BO₄] units to each other and it played as glass network former when the content was up to 10 mol%, accompanied by [BO₄] → [BO₃]. The stability of the glass improved first and then decreased as Al₂O₃ increased from 2 to 10 mol%, the glass with 5 mol% Al₂O₃ being the most stable one. The wetting behavior of the glasses indicates that excess Al₂O₃ leads to high sealing temperature. The glass containing 5 mol% Al₂O₃ characterized by a lower sealing temperature is suitable for SOFC sealing. Al₂O₃ improves the crystallization temperature of the glass. The crystal phases in the reheated glasses are mainly composed of Ba₂Si₃O₈, BaSiO₃, BaB₂O₄ and BaAl₂Si₂O₈. Al₂O₃ helps the crystallization of BaSiO₃ and BaAl₂Si₂O₈.     

Phase equilibrium in binary La2O3-Dy2O3 and ternary CeO2-La2O3-Dy2O3 systems

Cerium oxide doped with oxides of rare earth elements is a multifunctional material, a wide range of uses which is associated with its unique physicochemical properties. Phase diagrams of multicomponent systems are the physicochemical basis for the creation of new materials with improved characteristics.In this work, phase equilibria in ternary CeO₂–La₂O₃–Dy₂O₃ and binary La₂O₃–Dy₂O₃ systems in the whole concentration range were studied. No new phases have been identified in these systems. An isothermal section of the phase diagram of the CeO₂–La₂O₃–Dy₂O₃ system at a temperature of 1500 °С is constructed. No new phases have been detected in the system. It was found that in the studied ternary system solid solutions are formed on the basis of (F) modification of CeO₂ with structure of fluorite type, monoclinic (B), cubic (C) and hexagonal (A) modifications of Ln₂O₃.In the La₂O₃–Dy₂O₃ binary system (1500–1100 °С) three types of solid solutions are formed: based on hexagonal modification A-La₂O₃, monoclinic modification B-Dy₂O₃ and cubic modification C-Dy₂O₃ separated by two-phase fields (A+B) and (B+C), respectively. The boundaries of the regions of homogeneity of solid solutions based on A-La₂O₃ are determined by compositions containing 35–40, 20–25, 15–20 mol% Dy₂O₃ at 1500, 1250, 1100 °C, respectively. From the obtained data it follows that the solubility of Dy₂O₃ in the hexagonal modification of lanthanum oxide is 39 mol% at 1500 °C, 23 mol. % at 1250 °C and 16 mol% at 1100 °C. The limits of existence of solid solutions based on monoclinic B-modification are determined by compositions containing 30–35, 65–60 (1250 °С), 35–40, 55–60 (1100 °С) 40–45, 70–75 (1500 °C) mol% Dy₂O₃.In the studied system, with a decrease in temperature from 1500° to 1100°C, there is a decrease in the solubility of La₂O₃ in the crystal lattice of cubic solid solutions of C-type from 16 to 10 mol%.