In situ crystallization and elastic properties of transparent MgO–Al2O3–SiO2 glass‐ceramic

Glass‐ceramics (GC) generally possess enhanced mechanical properties compared to their parent glasses. The knowledge of how crystallization evolves and affects the mechanical properties with increasing temperature is essential to optimize the design of the crystallization cycle. In this study, we crystallized a glass of the MgO–Al₂O₃–SiO₂ system with nucleating agents TiO₂ and ZrO₂. The crystallization cycle comprised a 48 hour nucleation treatment at the glass‐transition temperature followed by a 10 hour growth step at a higher temperature. During this cycle, the evolution of crystalline phases was followed by high‐temperature X‐ray diffraction (HTXRD), which revealed the presence of karooite (MgO·2TiO₂), spinel (MgO·Al₂O₃), rutile (TiO₂), sillimanite (Al₂O₃·SiO₂), and sapphirine (4MgO·5Al₂O₃·2SiO₂). The same heat treatment was applied for in situ measurement of elastic properties: elastic modulus, E, shear modulus, G, and Poisson's ratio, ν. The evolution of these parameters during the heating path from room temperature to the final crystallization temperature and during the nucleation and the crystallization plateaus is discussed. E and G evolve significantly in the first two hours of the growth step. At the end of the crystallization process, the elastic and shear moduli of the GC were approximately 20% larger than those of the parent glass.     

P2O5‐Fe2O3‐CaO‐SiO2 ferromagnetic glass‐ceramics for hyperthermia

Ferromagnetic glass‐ceramics are an important kind of thermoseed material for hyperthermia treatments. In order to investigate the applications of glass‐ceramics in magnetic hyperthermia, P₂O₅‐Fe₂O₃‐CaO‐SiO₂ (PFCS) glass‐ceramics with different compositions were prepared by the sol‐gel method. The crystal phase, magnetic properties, induction heating ability, and cytotoxicity of the as‐prepared glass‐ceramics were investigated. The results show that all the samples exhibit low cytotoxicity and good induction heating ability. Moreover, it was found that the phosphorus content affected the crystal phase component of the sample, and thus influenced the induction heating ability. Results of the magnetic hyperthermia experiments showed that the PFCS glass‐ceramic samples induced significant cell death of the LoVo cancer cells. The highest cell death rate for sample B2P7 was more than 95%, which suggests good application prospects in the field of hyperthermia therapy.     

Fine Ti‐dispersed Al2O3 composites and their mechanical and electrical properties

Al₂O₃/Ti composites containing 0‐30 vol% dispersed fine Ti particles were fabricated using a hot‐press sintering method at 1500°C from mixtures of Al₂O₃ and TiH₂ powders. During sintering, TiH₂ decomposed to form metallic Ti. The effects of the Ti content on the mechanical and electrical properties of the composites were then investigated. No Ti‐Al intermetallic compounds were detected by X‐ray diffraction, and energy‐dispersive X‐ray spectroscopy indicated the presence of Al‐Ti‐O solid solution and Ti‐O phases. The composites showed enhanced densification; the measured densities were higher than the calculated theoretical values. Microstructural observation revealed homogeneously distributed fine Ti particles dispersed in the Al₂O₃ matrix. The Ti particle size ranged from submicrometer to a few micrometers depending on the Ti content. The fracture mode of the composites was primarily transgranular, in contrast to the intergranular fracture mode of monolithic Al₂O₃. Although the flexural strength was decreased with increase in Ti content, the composite containing 20 vol% Ti displayed the maximum fracture toughness of 4.3 MPa·cm^1/2, which was 37% greater than that of monolithic Al₂O₃. The composites containing more than 15 vol% Ti exhibited drastic decreases in resistivity (~10^?1 Ωcm), which were attributed to the formation of interconnected Ti networks at these Ti contents. The percolation threshold volume for electrical conduction in the present system was calculated to be 13.8 vol%. The results indicate that dispersing fine Ti particles into Al₂O₃ increased the fracture toughness and improved the conductivity of Al₂O₃.     

Effect of Microwave Processing on the Crystallization and Energy Density of BaO‐Na2O‐Nb2O5‐SiO2‐B2O3 Glass‐Ceramics

Barium sodium niobate (BNN) glass‐ceramics were successfully synthesized through a controlled crystallization method, using both a conventional and a microwave hybrid heating process. The dielectric properties of glass‐ceramics devitrified at different temperatures and conditions were measured. It was found that the dielectric constant increased with higher crystallization temperature, from 750°C to 1000°C, and that growth of the crystalline phase above 900°C was essential to enhancing the relative permittivity and overall energy storage properties of the material. The highest energy storage was found for materials crystallized conventionally at 1000°C with a discharge energy density of 0.13 J/cm³ at a maximum field of 100 kV/cm. Rapid microwave heating was found to not give significant enhancement in dielectric properties, and coarsening of the ferroelectric crystals was found to be critical for higher energy storage.     

Phase equilibria study and thermodynamic description of the BaO‐CaO‐Al2O3 system

A combined experimental investigation and thermodynamic assessment was performed for the BaO‐CaO‐Al₂O₃ system. By using a high‐temperature equilibration/quenching technique and scanning electron microscopy, electron probe microanalysis, and X‐ray powder diffraction analysis, the phase equilibria at 1500°C and phase stability of BaCa₂Al₈O₁₅ phase were determined. An extensive literature survey was conducted for the experimental and thermodynamic modeling data of the BaO‐CaO‐Al₂O₃ system. According to the literature data and the present measurements, a thermodynamic assessment was made in order to obtain a set of self‐consistent thermodynamic parameters to describe the BaO‐CaO‐Al₂O₃ system. Based on the thermodynamic parameters acquired in this work, isothermal sections at 1100°C, 1250°C, 1400°C, 1475°C, and 1500°C and the BaO·Al₂O₃‐CaO·Al₂O₃ and BaO·6Al₂O₃‐CaO·6Al₂O₃ joints were calculated and compared with the available experimental data.     

A new low‐firing and high‐Q microwave dielectric ceramic Li9Zr3NbO13

The microwave dielectric ceramic Li₉Zr₃NbO₁₃ was found and investigated. Prepared via the solid‐state reaction method, the Li₉Zr₃NbO₁₃ formed as a Li₂ZrO₃‐type solid solution at 880‐900°C, with monoclinic structure in C2/c space group and Z = 4. Typically, the Li₉Zr₃NbO₁₃ sintered at 900°C exhibited the excellent microwave dielectric properties of ε_r = 21.3, Q×f = 43 600 GHz (at 7.4 GHz), τ_f = 7.3 ppm/°C.     

Ultralow-permittivity glass /Al2O3 composite for LTCC applications

In the field of low temperature co-fired ceramic (LTCC), it remains a challenge to design the performance of LTCC with low permittivity less than 5. Here, a novel glass mixture of K-Al-B-Si-O (KABS) and Zn-B-Si-O (ZBS) is introduced as a sintering aid of alumina to obtain ultralow-permittivity glass/Al₂O₃ composite. Meanwhile, the factors of glass mixture component on microstructure, phase structure and dielectric properties of the composites are considered systematically. The crystal structure measured by X-ray diffraction (XRD) shows that pure crystalline phase of ZnAl₂O₄ spinel can be attained by tailoring the component of the glass mixture. In case of mass ratio of KABS: ZBS equal to 6:4, it favors to efficiently increase the sintering densification of composite, and significantly benefit the low dielectric loss, good mechanical and thermal performances. In detail, the optimal glass/ceramic composites sintered at 850 °C for 2 h exhibit the bulk density of 2.89 g/cm3, ε_r of 4.92 at 14 GHz and Q × f of 6873 GHZ, flexural strength of 202 MPa, thermal expansion coefficient of 5.5 ppm/°C. The above study provides an effective approach for preparing the novel composites as a promising candidate for LTCC applications.     

Microwave dielectric properties of SnO‐SnF2‐P2O5 glass and its composite with alumina for ULTCC applications

Ultralow‐temperature sinterable alumina‐45SnF₂:25SnO:30P₂O₅ glass (Al₂O₃‐SSP glass) composite has been developed for microelectronic applications. The 45SnF₂:25SnO:30P₂O₅ glass prepared by melt quenching from 450°C has a low T_g of about 93°C. The SSP glass has ε_r and tanδ of 20 and 0.007, respectively, at 1 MHz. In the microwave frequency range, it has ε_r=16 and Q_u × f=990 GHz with τ_f=?290 ppm/°C at 6.2 GHz with coefficient of thermal expansion (CTE) value of 17.8 ppm/°C. A 30 wt.% Al₂O₃ ‐ 70 wt.% SSP composite was prepared by sintering at different temperatures from 150°C to 400°C. The crystalline phases and dielectric properties vary with sintering temperature. The alumina‐SSP composite sintered at 200°C has ε_r=5.41 with a tanδ of 0.01 (1 MHz) and at microwave frequencies it has ε_r=5.20 at 11 GHz with Q_u × f=5500 GHz with temperature coefficient of resonant frequency (τ_f)=?18 ppm/°C. The CTE and room‐temperature thermal conductivity of the composite sintered at 200°C are 8.7 ppm/°C and 0.47 W/m/K, respectively. The new composite has a low sintering temperature and is a possible candidate for ultralow‐temperature cofired ceramics applications.     

A low sintering temperature glass based on SiO2–P2O5–ZnO–B2O3–R2O system for white LEDs with high color rendering index

A low sintering temperature glass based on the SiO₂–P₂O₅–ZnO–B₂O₃–R₂O (R=K and Na) system was studied as a matrix for embedding phosphors to fabricate color tunable white LEDs. The proposed system, which uses no heavy‐metal elements and can be sintered at 500°C, incorporates thermally weak commercial phosphors such as CaAlSiN₃:Eu²⁺ to produce phosphor‐in‐glasses (PiGs). Changing the mixing ratio of glass to phosphors affected the photo‐luminescence spectra and color coordinates of the PiGs when mounted on a blue LED. The color rendering index (CRI) and color correlated temperature (CCT) of the LEDs were also varied with the mixing ratio, providing color tunable white LEDs. A high CRI, up to 93, as well as highly improved thermal stability were obtained, along with a low sintering temperature compared to other glass systems, suggesting the practical feasibility of the proposed system.     

CaO- ZnO-B2O3-SiO2玻璃/Al2O3低温共烧复合陶瓷基板研究

用CaO-ZnO-B2O3-SiO2玻璃和氧化铝陶瓷复合材料制备了低温共烧陶瓷基板.在CaO-B2O3-SiO2微晶玻璃中引入ZnO,玻璃微晶化后的主晶相仍为硅灰石,但它的软化温度有不同程度的降低,同时析晶温度也有了显著的改变.特别是以ZnO部分取代CaO时,析晶温度明显提高.该玻璃与氧化铝复合可以在较宽的温度范围内烧结.在850℃/30 min烧结,得到了气孔率为1%、介电常数εr = 7.10的陶瓷基板材料.     

Mid‐IR transparent TeO2‐TiO2‐La2O3 glass and its crystallization behavior for photonic applications

In this report, effect of enhanced rare earth (La₂O₃) concentration on substitution of TeO₂ within ternary TeO₂‐TiO₂‐La₂O₃ (TTL) glass system has been studied with respect to its thermal, structural, mechanical, optical, and crystallization properties with an aim to achieve glass and glass‐ceramics having rare‐earth‐rich crystalline phase for nonlinear optical and infrared photonic applications. DSC analysis (10°C/min) demonstrates a progressive increase in glass‐transition temperature (T_g) from 359 to 452°C with the increase in La₂O₃ content. Continuous glass network modification with transformation of [TeO₄] to [TeO₃/TeO₃₊₁] units is evidenced from Raman spectra which is corroborated with XPS studies. While mechanical properties demonstrate enhancement of cross‐linking density in the network. These glasses exhibit optical transmission window extended from 0.4 to 6 μm with calculated zero dispersion wavelength (λ_ZDW) varying from 2.41 to 2.28 μm depending upon La₂O₃ content. Crystallization kinetics of TTL10 (80TeO₂‐10TiO₂‐10La₂O₃ in mol%) glass has been studied via established models. Activation energy (E_a) has been evaluated and dimensionality of crystal growth (m) suggests formation of surface crystals. Glass‐ceramic with crystalline phase of La₂Te₆O₁₅ has been realized in heat‐treated TTL10 glass samples (at 450°C). As predicted from DSC analysis, FESEM study unveils the formation of surface crystallized glass‐ceramics.     

Synthesis of Eu3+‐doped BaBi2Ta2O9 based glass‐ceramic nanocomposites: Optical and dielectric properties

In this paper we report for the first time synthesis of Eu³⁺‐doped transparent glass‐ceramics (TGC) with BaBi₂Ta₂O₉ (BBT) as the major crystal phase using the glass system SiO₂–K₂O–BaO–Bi₂O₃–Ta₂O₅ by melt quenching technique followed by controlled crystallization through ceramming heat treatment. DSC studies were conducted in order to determine a novel heat‐treatment protocol to attain transparent GCs by controlling crystal growth. The structural properties of the BBT GCs have been investigated using XRD, FE‐SEM, TEM and FTIR reflectance spectroscopy. Optical band gap energies of the glass‐ceramic samples were found to decrease with respect to the precursor glass. An increased intensity of emission along with increase in the average lifetime of Eu³⁺ was observed due to incorporation of Eu³⁺ ions into the low‐phonon energy BBT crystal site. The local field asymmetric ratios of all the samples were observed greater than unity. The dielectric constant (ε_r), dielectric loss, and dissipation factor values of both the base glass and ceramized samples were found to decrease with increase in frequency.     

Hierarchical growth of BiOCl on SrO‐Bi2O3‐B2O3 glass‐ceramics for self‐cleaning applications

We have grown hierarchical structure of bismuth oxycloride (BiOCl) on SrO‐Bi₂O₃‐B₂O₃ (SBBO) transparent glass‐ceramic. SBBO glass‐ceramics were fabricated via conventional melt‐quenching technique while BiOCl was grown by etching the glass via HCl. Enhanced visible light driven photocatalytic activity and increasing hydrophobic feature were observed on BiOCl grown SBBO than as‐quenched SBBO glass‐ceramics. Contact angle analysis showed maximum contact angle of 130.7° on the surface of most BiOCl grown SBBO glass‐ceramic. Furthermore, under visible light illumination water contact angle decreased from 130.7° to 30.8°. Such photo‐induced hydrophilicity and catalytic performance in translucent glass‐ceramics lead self‐cleaning applications.     

Multialloying effect on thermophysical properties of Cr7C3‐type carbides

The alloying element effect on the thermophysical properties of Cr₇C₃‐type ceramics is essential for the applications. The thermal expansion for these compounds is calculated using quasi‐harmonic approximation combined with density functional theory. The linear expansion coefficient along [100] direction is larger than that along [010] and [001] direction. The B‐ and Mo‐codoped Fe₄Cr₃C₃ has the smallest thermal expansion coefficient. We obtained the temperature dependence of bulk modulus, pressure derivative modulus, and the Grüneisen constants. Furthermore, we propose a new method to calculate the anisotropy of minimum thermal conductivity which is suitable to the large complex unit cells. The three‐dimensional (3D) expression of anisotropy of minimum thermal conductivity are presented companied with planar projections on (100), (010), (001), and (110) crystal planes. The minimum thermal conductivity of Fe₃Cr₃WC₂B is lower than other multicomponent compounds. The charge density differences and chemical bonding between Mo/W and B are found to be the key factor on the thermophysical properties of these compounds.     

BaO-Al2O3-B2O3-SiO2玻璃/SiO2高膨胀低温共烧陶瓷研究

用BaO-Al2O3-B2O3-SiO2玻璃与二氧化硅复合的方法制备了高膨胀系数低温共烧陶瓷。实验首先制备一组玻璃材料,通过热膨胀测试、DTA等方法研究了玻璃的热学性能,然后用玻璃与石英、方石英和鳞石英晶体按一定比例复合制得高膨胀低温共烧陶瓷。通过烧结试验、XRD等分析方法研究了复相陶瓷材料的烧结收缩性能、晶相组成、热膨胀系数和介电常数。结果表明:50%BaO-7.5%Al2O3-30%B2O3-12.5%SiO2玻璃具有较低的转变温度(520℃)。该玻璃与鳞石英晶体以1:1的比例复合,850℃/10min烧结可以获得热膨胀系数为12.18×10-6K-1、介电常数为5.37的低温共烧陶瓷。     

Effect of Li2O on the defect polarization in CuO‐added (K0.9Na0.1)NbO3 piezoelectric ceramics

CuO‐added (Li_xK_0.9?xNa_0.1)NbO₃ [C(L_xK_0.9?xN_0.1)N] ceramics with 0.0≤x≤0.05 were well‐sintered at 960°C for 6 hours. The lattice parameters of the specimens decreased with the addition of Li₂O. Defect polarization (P_D) formed between Cu²⁺ions and oxygen vacancies. Double polarization vs electric field (P‐E) hysteresis and sprout‐shaped strain vs electric field (S‐E) curves were observed in these specimens with a large strain of 0.16% at 7.0 kV/mm, possibly owing to the presence of P_D. When the P‐E curve was measured at temperatures higher than 75°C, the C(K_0.9N_0.1)N ceramic exhibited a normal P‐E hysteresis curve, whereas the C(L_0.04K_0.86N_0.1)N ceramic maintained the double P‐E hysteresis curve up to 125°C, indicating that Li₂O increased the thermal stability of P_D. The latter specimen also showed the sprout shaped S‐E curve with a strain of 0.15% at 7.0 kV/mm after 10⁴ cycles of a high electric field of 7.0 kV/mm.     

YCrO3/Al2O3 Core‐Shell Design: The Effect of the Nanometric Al2O3‐Shell on Dielectric Properties

We report a novel strategy to improve the dielectric properties of the biferroic YCrO₃ ceramic compound through interface conduction control by means of an insulating Al₂O₃ using a core‐shell design. The YCrO₃ particles were covered with several layers of insulating Al₂O₃ using the atomic layer deposition technique to produce the core‐shell structure. TEM images reveal homogeneous and well‐defined Al₂O₃ coatings of ~8, ~60, and ~130 nm thickness. XRD shows the Al₂O₃‐shell to be amorphous. The dielectric characteristics of the sintered nano‐composite were investigated in the 100 Hz–1 MHz frequency range and temperature between 300 and 580 K. As the Al₂O₃‐shell thickness covering the YCrO₃ particles is increased, a decrease of the dielectric permittivity, loss tangent and AC conductivity values was found in the whole range of temperatures and frequencies. Furthermore, the rounded hysteresis loop, typical of conductive ceramic is restored as the insulating Al₂O₃ layer becomes thicker. This behavior is explained because the insulating Al₂O₃‐shell acts as internal barrier layer localizing the surface charges on the sintered grain boundaries. This fact was confirmed by Electron Beam Induced Current technique where a clear contrast at the grain boundaries confirms the charge localization at the YCrO₃/Al₂O₃ interface. These results also reveal that the Al₂O₃‐shell induces another conductive mechanism when the insulating Al₂O₃ layer becomes thicker. Nonetheless, this new strategy is an effective approach to suppress the parasitic conductivity in polycrystalline multiferroic ceramics and increasing thus the multifuncionality.     

High Na‐ion conducting Na1+x[SnxGe2−x(PO4)3] glass‐ceramic electrolytes: Structural and electrochemical impedance studies

Na‐ion conducting Na_1+x[Sn_xGe_2?x(PO₄)₃] (x = 0, 0.25, 0.5, and 0.75 mol%) glass samples with NASICON‐type phase were synthesized by the melt quenching method and glass‐ceramics were formed by heat treating the precursor glasses at their crystallization temperatures. XRD traces exhibit formation of most stable crystalline phase NaGe₂(PO₄)₃ (ICSD‐164019) with trigonal structure. Structural illustration of sodium germanium phosphate [NaGe₂(PO₄)₃] displays that each germanium is surrounded by 6 oxygen atom showing octahedral symmetry (GeO₆) and phosphorous with 4 oxygen atoms showing tetrahedral symmetry (PO₄). The highest bulk Na⁺ ion conductivities and lowest activation energy for conduction were achieved to be 8.39 × 10^?05 S/cm and 0.52 eV for the optimum substitution levels (x = 0.5 mol%, Na_1.5[Sn_0.5Ge_1.5(PO₄)₃]) of tetrahedral Ge⁴⁺ ions by Sn⁴⁺ on Na–Ge–P network. CV studies of the best conducting Na_1.5[Sn_0.5Ge_1.5(PO₄)₃] glass‐ceramic electrolyte possesses a wide electrochemical window of 6 V. The structural and EIS studies of these glass‐ceramic electrolyte samples were monitored in light of the substitution of Ge by its larger homologue Sn.     

Molecular simulation of the glass transition and proton conductivity of 2,2′‐benzidinedisulfonic acid and 4,4′‐diaminodiphenylether‐2,2′‐disulfonic acid‐based copolyimides as polyelectrolytes for fuel cell applications

The glass transition temperatures (T_gs) and proton conductivities of polyimides synthesized from naphthalene‐1,4,5,8‐tetracarboxylic dianhydride (NTDA), 2,2′‐benzidinedisulfonic acid (BDSA), 4,4′‐diaminodiphenylether‐2,2′‐disulfonic acid (ODADS), and non‐sulfonated diamine monomers have been predicted using molecular dynamics simulations. The specific volumes for two dry and four hydrated NTDA‐based polyimides were plotted versus temperatures above and below T_gs to obtain the glass transition temperatures. The simulation results suggest that the ODADS‐based polyimide membranes exhibit lower T_gs and thus better mechanical properties than the BDSA‐based polyimides, which may be attributed to the high mobility of backbones of ODADS as supported by the vectorial autocorrelation function (VACF) results of this study. In addition, comparison of the simulated T_gs for the dry and hydrated ODADS‐based polyimides has shown that water content in polyimides can affect their T_gs. The proton conductivities of a representative polyimide in both dry and hydrated conditions have been obtained from molecular dynamics simulations of the proton and hydronium ion diffusion. The simulated conductivity for the hydrated NTDA‐ODADS/BAPB cell is in reasonable agreement with the experimental value obtained from the AC impedance method. The relationship between the chemical composition, chain flexibility, and the glass transition and proton conduction of these NTDA‐based polyimides was explored on the basis of VACF and pair correlation function analysis. Copyright © 2006 Society of Chemical Industry     

Investigation of Sm2O3 additive on mechanical and electrical properties of Li2O‐ stabilized β″‐alumina electrolyte

Li₂O‐ stabilized β″‐alumina was synthesized by the double zeta process. The effect of Sm₂O₃ additive as the sintering aid, on microstructure, mechanical and electrical properties of Li₂O‐ stabilized β″‐alumina ceramics was studied by means of X‐ray diffraction, field emission scanning electron microscope, biaxial flexure test and ionic conductivity measurement. The results indicated that both the fracture strength and the ionic conductivity of the sample containing 0.2 wt% Sm₂O₃ improved approximately 52% and 54%, respectively, that can be attributed to its higher density, higher amount of β″‐Al₂O₃ phase and more uniform microstructure.