Glass-ceramics of barium strontium titanate for high energy density capacitors

Barium strontium titanate glass-ceramics were successfully produced with one major crystalline phase when Al₂O₃ was added to the melt. A dielectric constant of 1000 and a breakdown strength of 800 kV/cm was achieved; however the energy density was only measured to be 0.3–0.9 J/cm³. These energy density values were lower than anticipated due to the presence of dendrites and pores in the microstructure. Using BaF₂ as a refining agent improved the microstructure and doubled the energy density for BST 80/20 samples. However, no refining agent reduced the increasing amount of hysteresis that developed with increasing applied electric field. This phenomenon is believed to be due to interfacial polarization.     

Microstructure,residual stresses,and mechanical performance of surface crystallized translucent glass-ceramics

Mechanical properties of glasses can be significantly increased by inducing surface crystallization of a low coefficient of thermal expansion phase. In this work, we produced surface crystallized lithia-alumina-silica glass-ceramics with different crystallized layer thicknesses and analysed the resulting residual stresses and their effect on mechanical properties. The residual stress magnitude was estimated by analytical and experimental methods, as well as numerical modeling. The surface compressive stress reached 390 MPa and 490 MPa, as given by the analytical and experimental determination, respectively. These stresses prevented radial cracking in microhardness and scratch tests. The best glass-ceramic achieved a Vickers hardness of 7.5 GPa and fracture strength of 680 ± 50 MPa in a ball-on-three-ball test. These glass-ceramics are translucent, providing 50–60% transmittance over the visible wavelength spectrum (1.3 mm-thick-sample). This study unveiled the causes of improved mechanical properties and validates the concept that surface crystallization is a valuable technique for developing high strength glass-ceramics.     

Effects of Sr substitution for Ba on dielectric and energy-storage properties of SrO-BaO-K2O-Nb2O5-SiO2 glass-ceramics

In this work, [xSrO, (1 − x)BaO]-K₂O -Nb₂O₅-SiO₂ (SBKNS, x = 0.2, 0.4, 0.6, 0.8) glass-ceramics were synthesized through the controlled crystallization method. The phase structure, dielectric and energy-storage properties were systematically studied through the Sr substitution for Ba. It was found that the dielectric properties were improved due to the formation of solid liquid phase Sr_0.5Ba_0.5Nb₂O₆. Breakdown strength firstly increases and then decreases, which strongly depends on the variation in interfacial polarization. The highest value of breakdown strength reaches 1828 ± 88 kV/cm for x = 0.4, which is attributed to more uniform and dense microstructure and lower interfacial polarization. Correspondingly, the optimized theoretical energy-storage density reaches up to 17.45 ± 0.74 J/cm³. The maximum of discharged energy-storage density of 1.45 J/cm³ from P-E loop was acquired under electric field of 500 kV/cm. Moreover, discharged power density of the capacitor was evaluated and reached a high value of 1.76 MV/cm³ in pulsed charged-discharged circuit.     

Strength behaviour of etched Zerodur®

Zerodur^® is a well-known glass-ceramic used for optical components because of its unequalled dimensional stability under changing temperature. For example, it is used for mirrors of space telescopes. Due to the large amount of material that has to be removed during fabrication of the mirrors a rather coarse grit is used for grinding. Strength limiting defects introduced by this procedure are eliminated by removing the damaged surface layer by etching to achieve a high strength.Through a large test campaign comprising a high number of strength specimens (>160) of various types and sizes, the validity of the Weibull strength statistics was investigated. The purpose was to accurately determine the parameters of the Weibull law for Zerodur^® when treated in the same conditions as mirrors.As a rule of thumb the average strength of Zerodur^® is assumed to be around 10 MPa. The measured strength is much higher. The strength distributions showed unexpected results, especially the absence of the expected size effect. Through a thorough fractographic analysis it was shown what kind of defects were responsible for failure of etched Zerodur^® and why the prerequisites for the validity of the Weibull theory were not fulfilled in the investigated specimens.     

Absence of surface flaking in hierarchical glass-ceramic coating: High impact resistant ceramic tiles

The impact resistance method is a useful procedure to determine the tile resistance. While other works are focused on modifying the tile support to improve the impact resistance, in this work, a new glass-ceramic material was developed to used it as glaze coating in order to relax impact tensions. This material possesses a hierarchical nano-microstructure consisted of microcrystal surrounded by nanostructured regions having low glassy phase, which is considered responsible for tension relaxations. The resilience coefficient measured in conventional and glass-ceramic glazes presents little differences (0.85–0.88). However, impact damages on the surface is totally inhibited for glass-ceramic coating while the conventional one suffers great flaking. These damages were analyzed by Optical profilometry and FESEM to compare the impact resistance and to correlate it with its microstructure. The results confirm that the micro-nanostructured coating paves the way to improve impact resistance in ceramic materials where surface damage is a critical parameter.     

Bioactivity and antibacterial activity against E-coli of calcium-phosphate-based glasses: Effect of silver content and crystallinity

In this work we developed improved bioactive glasses and glass-ceramics for biomedical applications, investigating their in vitro bioactivity, biocompatibility and antibacterial properties against E-Coli. A melt-quenched bioactive glass of the SiO₂-CaO-P₂O₅-MgO system was modified with the addition of 1 and 2 mol% Ag₂O and the 1 mol% Ag₂O-containing glasses were then heat treated to produce glass-ceramics. Surface modifications after soaking in SBF and ionic concentration changes showed that addition of silver and crystallization did not affect bioactivity although crystalline phases promoted a decrease in the degradation rate.Biocompatibility of all Ag-containing glasses and glass-ceramics was confirmed for certain samples concentrations. The antibacterial activity of the glasses against E-Coli was generally improved with decreasing particle size or increasing Ag₂O. The Ag-containing glass-ceramics with higher content of crystalline phase appears as a promising biocompatible biocidal material with potential applications in bone-related diseases.     

CaO—Al2O3—SiO2系统微晶玻璃烧结过程研究

本文利用一系列等温烧结收缩曲线，通过计算得到各组分玻璃的表观烧结活化能，继而分析讨论了玻璃成分，烧结温度等因素对玻璃颗粒烧结过程的影响，提出最佳的烧结工艺制度。     

Crystal growth induced by Nd:YAG laser irradiation in patterning glass ceramic substrates with dots

In this work a glass ceramic substrate was processed by focusing a laser beam inside the said material. The crystal phase within the amorphous matrix provides mechanical properties to the glass ceramic substrate in such a way that dots can be patterned inside the fore-mentioned material without producing any cracks. These marks are made up of crystals, the growth of which has been induced by the laser beam. These inner structures can modify the optical, thermal and mechanical properties of the glass ceramic substrate.A Q-switched Nd:YAG laser at its fundamental wavelength of 1064 nm with pulsewidths in the nanosecond range has been used.Morphology, composition, microstructure, mechanical and thermal properties of the processed material are described.     

Ionic conduction through heterogeneous solids: Delineation of the blocking and space charge effects

The conductivities of an ionic polycrystalline solid lithium iodide (LiI) and covalent, polycrystalline lithium aluminum titanium phosphate (LATP) glass-ceramic material with Al₂O₃ and Ba_0.6Sr_0.4TiO₃ (0.6BST) additions were investigated. It was determined that blocking and space charge effects coexist in these heterogeneous solids. However, their magnitudes differ from one system to another. The most pronounced blocking effect was evident in the LATP–Al₂O₃ system, whereas a dominant space charge effect was observed in the LiI–Al₂O₃ system. The higher dielectric constant of 0.6BST enhanced space charge effect in the LATP–0.6BST system. The space charge effect was also found to be temperature dependent.