Chemically Strengthened Low Crystallinity Black Glass-Ceramics with High Liquidus Viscosities

Strong, black materials are needed for electronic device backs and appliance facings. While glass-ceramics have good strength and toughness, their liquidus viscosity is too low to enable economical forming of these devices by the fusion or slot draw methods. Thus, we invented a new class of low crystallinity glass-ceramics with 10–20 nm crystallites in the Fe₂O₃-TiO₂-MgO system. These materials were formed into transparent glasses and then heat treated to make black opaque glass-ceramics containing magnetite, pseudobrookite, and/or ε-Fe₂O₃. The ε-Fe₂O₃ phase exhibited extensive solid solution (ss) between Fe₂O₃ and MgTiO₃. The blackness and opacity of the ε-Fe₂O₃ glass-ceramics peaked at a ceram temperature of 750°C where the Fe²⁺ in the crystallites was maximized, resulting in peak Fe²⁺-Ti⁴⁺ charge transfer absorption. The liquidus viscosity was increased to more than 100 kPa*s by optimizing the base glass composition and minimizing the amount of crystallinity, thereby enabling fusion formability. These fusion formable glass-ceramics had strengths exceeding the best commercially available glasses after ion exchange. This work provides a new class of low crystallinity fusion formable glass-ceramics with high strength.     

Effect of substitution of ZrO2 by SnO2 on crystallization and properties of environment-friendly Li2O–Al2O3–SiO2 system (LAS) glass-ceramics

In this study, a transparent and environmentally friendly Li₂O–Al₂O₃–SiO₂ (LAS) glass-ceramic was prepared by melt-quenching and two-step heat treatment. The influence of the substitution amount of ZrO₂ by SnO₂ on the crystallization, microstructure, transparency, and mechanical properties of LAS glass and glass-ceramics was investigated by means of differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible Spectrophotometer, three-point bending strength test, and microhardness test. The results indicate that the main crystalline phase of LAS glass ceramics was a β-quartz solid solution when heat treated at 780 °C for 2 h and 870 °C for 1.5 h. When the substitution amount of ZrO₂–SnO₂ increased from 0.4 mol% to 2.5 mol%, the grain size and thermal expansion coefficient of LAS glass-ceramics first decreased and then increased, and the crystallinity first increased and then decreased. When the substitution amount of ZrO₂–SnO₂ was 0.8 mol%, the transparency of the LAS glass-ceramics was maximum, the bending strength was 96 MPa, and the Vickers hardness was 10.9 GPa.     

First ZnGa2O4 transparent ceramics

Transparent polycrystalline ZnGa₂O₄ ceramics are synthesized, for the first time, by combining high-energy ball milling, solid-state reaction and spark plasma sintering. They appear transparent in both the visible and near infrared (up to 9 μm) ranges after a post-SPS annealing in air converting the raw semiconductor into an electrical insulator. The maximum of transmittance is reached in the near infrared region, at around 2.5 μm, with a value of 78 % (1 mm thick sample) close to the maximum value of transmittance previously measured for single crystals. These transparent ceramics present a classic cubic spinel ZnGa₂O₄ structure and a dense microstructure (> 99 %) attained without sintering aids, with an average grain size of 600 nm and a random orientation of the crystallites. TEM observations performed on thin foils have revealed limited nanometer scale intergranular porosity which does not affect much the transparency. As a proof of interest, red long-lasting luminescence arising from the entire sample volume is observed in these Cr³⁺ doped transparent ceramics. This innovative work is anticipated to further drive the development of transparent ZnGa₂O₄ ceramics towards a wider range of performing optical applications such as laser emission.     

Effects of Al2O3 addition on microstructure and luminescence of transparent germanosilicate glass-ceramics with incorporated spinel Ga-oxide nanocrystals

Ga-oxide spinel nanocrystals are wide band gap systems, which can be incorporated in a glass matrix by phase separation mechanisms. In suitable conditions, this kind of processes can give rise to transparent nanostructured glass-ceramics with UV excitation and luminescence properties potentially interesting in several technological areas. Nanophase size dispersion and volume fraction have been demonstrated to be controllable, at some extent, by suitable thermal treatments for nucleation and nano-crystallization in low-alkali gallium germanosilicate system. Here we report the results on the role of Al₂O₃ additions on the microstructure and optical response of the glass-ceramics fabricated in this system. Data of differential scanning calorimetry, X-ray diffraction, transmission electron microscopy, absorption and fluorescence spectroscopy show that Al₂O₃ addition, up to 4.5 mol%, turns out to have a considerable impact on the size and number density of precipitated nanocrystals, which are solid solutions of γ-Ga_2-xAl_xO₃ resulting from the partial incorporation of Al³⁺ ions into the crystalline phase. We show that the use of Al₂O₃ as an additive in the composition of gallium germanosilicates facilitates glass melting and leads to glass-ceramics with significantly modified photoluminescence characteristics such as decay lifetime and integrated intensity of light emission. The possible reasons are discussed.     

Optical and mechanical properties of amorphous bulk and eutectic ceramics in the HfO2–Al2O3–Y2O3 system

Bulk glasses containing HfO₂ nano-crystallites of 20–50 nm were prepared by hot-pressing of HfO₂–Al₂O₃–Y₂O₃ glass microspheres at 915 °C for 10 min. By annealing at temperatures below 1200 °C, the bulk glasses were converted into transparent glass-ceramics with HfO₂ nano-crystallites of 100–200 nm, which showed the maximum transmittance of ～70% in the infrared region. An increase of annealing temperature (>1300 °C) resulted in opaque YAG/HfO₂/Al₂O₃ eutectic ceramics. The eutectic ceramics contained fine Al₂O₃ crystallites and showed a high hardness of 19.8 GPa. The fracture toughness of the eutectic ceramics increased with increasing annealing temperature, and reached the maximum of 4.0 MPa m^1/2.     

Study on the effect and mechanism of zirconia on the sinterability of yttria transparent ceramic

Transparent Y₂O₃ ceramics were fabricated by solid-state reaction using high purity Y₂O₃ and ZrO₂ powder as starting material. The results indicated that ZrO₂ additive can improve the transparency of Y₂O₃ ceramic greatly. The best transmittance appears with 3 at.% ZrO₂ doped Y₂O₃ transparent ceramic with transmittance at 1100 nm of 83.1%, which is up to 98.6% of the theoretical value. The microstructure is uniform and no secondary phase is observed in the ceramic with the average grain size of 15 μm. The mechanism of ZrO₂ improving the transparency of Y₂O₃ ceramic is analyzed in detail. On this basis, Yb³⁺ doped Y₂O₃ transparent ceramic was also fabricated and spectroscopic properties were investigated.     

Fabrication and optical properties of transparent fine-grained Zn1.1Ga1.8Ge0.1O4 and Ni2+ (or Cr3+)-doped Zn1.1Ga1.8Ge0.1O4 spinel ceramics

For the first time, a Zn_1.1Ga_1.8Ge_0.1O₄ transparent spinel ceramic has been fully densified by spark plasma sintering. XRD measurements show that this ceramic is composed of a pure cubic spinel phase. SEM analysis revealed a homogeneous and dense microstructure with the average grain size being 200 ± 100 nm. The transmittance of these fine-grained ceramics reached 70 % in the visible range and is very close to 80 % at 2 µm, thus close to the T_max value deduced from the measurement of the refractive index. The ceramics exhibit excellent mechanical properties with a Young modulus of 222 GPa, a Vickers hardness of 14.25 GPa and a thermal conductivity of 7.3 W.m⁻¹. K⁻¹. By doping with Cr³⁺ ions, transparent Zn_1.1Ga_1.8Ge_0.1O₄ ceramics present both a red luminescence and a long-lasting afterglow during several minutes. Moreover, a near infrared broadband emission at 1.3 µm is also achieved with Ni²⁺ ions.     

Issue Information

Cover Photograph: TEM images highlighting the uniform microstructure of the transparent glass-ceramic A (a, b) compared to the non-uniform microstructure of the opaque glass-ceramic B (c, d). The darkest regions are residual glass. The brighter regions are spinel and tet ZrO₂ crystallites, where the brightest regions can be either the highest-Z (atomic number) crystallites (ZrO₂) or an integration of lower-Z crystallites through the depth of the material. https://doi.org/10.1111/jace.17129

     

Optical Active Nano-Glass-Ceramics

This paper reviews the synthesis and characterization of several transparent glass-ceramics with optical active nanocrystals. Glass-ceramics containing ferroelectric Sr_xBa_1-xNb₂O₆ nanocrystals with an ellipsoidal shape show optical phase modulations in the presence of alternative electric fields. In the glass-ceramics with Ba₂TiSi₂O₈ (BTS) nanocrystals, BTS crystalline layers with a thickness of approximately 120 nm are formed at the surface and ellipsoidal-shaped crystallites with a diameter of 100–200 nm are dispersed in the glass matrix. Some TeO₂-based and GeO₂-based glasses show a prominent nanocrystallization. RE-doped CaF₂ nanocrystals are patterned in a spatially selected region by laser irradiations. The size, morphology, and dispersion state of nanocrystals should be carefully checked in each glass system and composition. The basic concept for the design of glass system and composition is also discussed. Some data on optical active performances in transparent glass-ceramics with nanocrystals were introduced.     

Contribution of some transition metal oxides to crystallization and electro-thermal properties of glass-ceramics

Lithium di-silicate (LS₂) glass-ceramics modified with copper oxide using the formula: 34.83Li₂O–xCuO–(65.17-x)SiO₂ (where; x = 1, 2, 4 and 6 mol%) were prepared by melt-quenching followed by controlling heat-treatment. 6 mol% of MnO or Fe₂O₃ transition metal oxides was added instead of SiO₂ in the high CuO-content composition. The effect of the transition cations on phase formation, microstructure, density, thermal expansion, and electrical conductivity was investigated as a function of the controlled crystallization. Results show that up to 4 mol%, Cu⁺² was hosted in stable Li₂Si₂O₅ structure. This enhanced the crystal formation, including Li₂Si₂O₅ and its solid solution (ss), Li₂SiO₃, Li₂Cu₅(Si₂O₇)₂, CuMn₆SiO₁₂, LiFeSi₂O₆ (ss), and the orthosilicate Li₂FeSiO₄ (ss). The prepared materials had different density values ranged from 2.35 to 2.79 g/cm³ for glass and varied from 2.43 to 3.15 g/cm³ for glass–ceramics, whereas the α-values of glass-ceramics ranged in the 95–165 × 10⁻⁷/°C. The progress of electrical properties in glass-ceramics, as a function of composition, was studied. It was markedly improved by adding different transition cations especially, Fe⁺³. The study reveals that the incorporation of transition metal ions in LS₂ composition has a positive effect on the physical-chemical properties of the prepared glass-ceramics. Therefore, it constitutes to prepare future glass-ceramic applications as hermetic seals of metals as well solid electrolyte materials.     

Improvement in structural,dielectric and energy-storage properties of lead-free niobate glass-ceramic with Sm2O3

Phase evolution, microstructure, dielectric performance, polarization, breakdown strength as well as energy-storage behaviors for the lead-free niobates glass-ceramics with Sm₂O₃ were systematically investigated. Two crystallographic structures of tetragonal tungsten bronze and orthorhombic perovskite complex phases were obtained and Sm³⁺ entered into the crystalline phases. The optimal microstructure of the glass-ceramic was obtained with Sm₂O₃ of 2 mol%. Both dielectric constant and polarizability were enhanced with increasing Sm₂O₃. The breakdown strength and energy-storage behaviors of the glass-ceramics were also improved by increased Sm₂O₃. The highest breakdown field of 21.2 kV/mm, the highest charged (0.74 J/cm³) and discharged energy density (0.45 J/cm³) were obtained in the glass-ceramic with 2 mol% Sm₂O₃. It is due to the reduced interfacial polarization in this particular composition.     

High-strength,translucent glass-ceramics in the system MgO-ZnO-Al2O3-SiO2-ZrO2

In a MgO/Al₂O₃/SiO₂/ZrO₂ glass-ceramic MgO was substituted by equimolar ZnO concentrations. The effect of this substitution on the crystallization behavior, the microstructure and the mechanical properties of the glass-ceramics was studied. The crystal phases and the microstructure were analysed by X-ray diffraction and scanning electron microscopy. Tetragonal ZrO₂, a high-/low-quartz solid solution (high-/low-QSS) and spinel/gahnite were observed in the entire bulk of the glass-ceramics. Additionally, indialite or cristobalite are detected at the surface of some glass-ceramics. The substitution of small ZnO concentrations induces an increasing low-QSS concentration and hence higher microhardness and Young’s modulus. By contrast, higher ZnO concentrations lead to a liquid/liquid phase separation in the glass. Moreover, spinel/gahnite is the main crystal phase and the concentration of the low-QSS is smaller in theses glass-ceramics which also do not show as good mechanical properties. However, the biaxial flexural strength of the glass-ceramics is not notably affected by the ZnO concentration.     

Densification and microstructure evolution of reactively sintered transparent spinel ceramics

Reactive sintering is an effective and simple method to prepare transparent spinel ceramics. In this research, transparent MgO·nAl₂O₃ (0.98?≤ n?≤?2) spinel ceramics were prepared via reactive sintering in air followed by hot isostatic press (HIP), using MgO and γ-Al₂O₃ powders as raw materials. The influence of composition on densification and microstructure evolution was systemically investigated. More importantly, the relationship between microstructure of presintered samples and final properties of transparent ceramics was singled out. Thermodynamically stable large pores were easily generated in magnesia-rich and stoichiometric samples after presintering in air, causing severe abnormal grain growth during the HIP treatment and poor optical quality of the resulting samples. The presintering temperature of alumina-rich samples widely varied with composition. No large pores were observed in the presintered sample, which was beneficial for the elimination of residual pores in the following HIP process. Highly transparent spinel ceramics with n?=?1.1 and 1.3 were successfully fabricated with the transmittance above 84% even at the short wavelength of 400?nm, close to the theoretical value.     

Thermo-magnetic properties of Fe2O3-doped lithium zinc silicate glass-ceramics for magnetic applications

The crystallization behaviour and thermo-magnetic characteristics of glass-ceramic based on the 15Li₂O–20ZnO–10CaO–55SiO₂ system doped with varied Fe₂O₃ additions (0.0125, 0.025, and 0.05 mol) are described in this work. In some cases, Al₂O₃ was also added to the iron-containing sample. Glasses were successfully prepared by melt-quenching technique and converted into glass-ceramics by controlled heat-treatment, using DTA, SEM, XRD, and VSM techniques. The density, thermal expansion coefficients (TCE), and magnetic characteristics of the glass-ceramic were examined. XRD results confirmed characteristic peaks for various phases like quartz, Li₂ZnSiO₄, wollastonite, Li₂Si₂O₅, ZnFe₂O₄, and β-spodumene. By doping Fe₂O₃ and Al₂O₃ with lowering annealing temperature, the particle size was reduce, resulting in glass-ceramics with a more uniform and dense microstructure. The density of glass-ceramics rises from 2.74 g/cm³ to 3.45 g/cm³, whereas the TCE values in average 14–78 × 10⁻⁷/°C with temperature range of 25–500 °C. The doped glass-ceramics have superior magnetic properties with saturation magnetization (0.143–0.548 emu/g), the coercivity force (65.116–86.359 G), and remanence magnetization (0.074–0.436 emu/g). Under an alternating magnetic field, the presence of the Zn-ferrite phase in the glass-ceramics improves their magnetic properties and increases their heat-generating capability. Certain features of the doped glass-ceramics control the extensive variety of possibilities for their usage in various magnetic applications particularly for cancer hyperthermia treatment.     

Optical transmittance and energy storage properties of potassium sodium niobate glass-ceramics

In this work, 0.8(K₂O-Na₂O-2Nb₂O₅)?0.2((1-x)B₂O₃-xP₂O₅) (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5) glass-ceramics have been fabricated. The effects of P₂O₅ on the microstructure and properties of the glass-ceramics were comprehensively studied. The addition of P₂O₅ promotes the transition of the glass network structure from a negatively charged [B?₄]^- tetrahedron to an electrically neutral [BP?₄] tetrahedron. With the increase of P₂O₅ content, the formation of K₂B₄O₇ is inhibited, with major phase of Na_0.9K_0.1NbO₃ and minor phase of K₂B₄O₇. It is found that the band gap width of the glass-ceramics increases from 3.34 eV to 3.52 eV firstly and then decreases to 3.43 eV. The grain size of the glass-ceramics decreases from 150 nm to 50 nm. High optical transmittance (63%), large discharge energy density (4.58 J/cm³) and large energy storage efficiency (98%) have been simultaneously obtained for K₂O-Na₂O-Nb₂O₅-B₂O₃-P₂O₅ glass-ceramics, which are potential for the applications of the transparent pulse capacitors.     

Ion beam assisted electron beam vacuum deposition of antireflective SiO2 coating on MgAl2O4 spinel

In this paper, the electron beam vacuum coating method was used to coat a SiO₂ film on an MgAl₂O₄ spinel substrate. The thickness of the coating was aimed to be 925 nm based on the physics of the antireflection coatings. Atomic force microscope images revealed that the coated silica was 880 nm thick, which is close to the aimed theoretical thickness and had 2.11 nm roughness. It could enhance the transparency of the spinel substrate by being coated on it. The infrared transmittance of the sample coated with SiO₂ film in the range of 3700 nm-4800 nm was measured by a Fourier transform infrared spectrometer and reached 92.5% to 78.5%, which was about 2%–4% higher than that of MgAl₂O₄ spinel. In addition, it was discovered that the bonding force between the coating and the substrate is determined to be about 200 MPa. The results of this study can be used for further precise design and production of antireflection coatings on the transparent materials that need more transparency.     

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.     

Efficient energy transfer of Ce to Nd in SrF2 transparent ceramics for enhancing NIR emission

High optical quality Nd³⁺ and Ce³⁺ co-doped SrF₂ (Nd³⁺, Ce³⁺: SrF₂) transparent ceramics were fabricated successfully by a simple hot-pressing (HP) method. The phase composition, in-line transmittance, absorption and emission spectra, as well as the detailed energy transfer of Nd³⁺ and Ce³⁺ were investigated. In addition, the Judd- Ofelt (J-O) theory was adopted to evaluate the luminescence property. The SrF₂ transparent ceramic samples exhibited excellent optical properties, up to 82 % at 400 nm and 92.5 % at 1054 nm. The fracture surface of SrF₂ transparent ceramic proved nearly dense microstructure and EDS results demonstrated uniform doping. The addition of cerium ions changed the crystal field environment of neodymium ions and shifted the emission peak to higher wavelengths at 796 nm excitation. Moreover, through the energy transfer process of Ce³⁺ to Nd³⁺, the occurrence of concentration quenching phenomenon was avoided under 298 nm excitation, and the emission cross-section of ⁴F_3/2→⁴I_11/2 increased to 3.1 × 10⁻²⁰ cm².     

Highly transparent Mg0.27Al2.58O3.73N0.27 ceramic fabricated by aqueous gelcasting,pressureless sintering,and post-HIP

Magnesium aluminum oxynitride (Mg_0.27Al_2.58O_3.73N_0.27, termed as MgAlON) ceramics with high transparency and complicated shape was prepared by aqueous gelcasting, pressureless sintering, and followed by hot isostatic pressing. No obvious hydration was found by the characterizations of X-ray diffraction, pH value, Fourier transform infrared and thermal analysis for the interaction between MgAlON spinel powders and water, leading to the stable MgAlON slurry with high solid loading (52 vol%) and low viscosity. This result may be due to different composition of MgAlON from that of MgAl₂O₄ and AlON. Besides, transparent MgAlON ceramic (1.95 mm in thickness) with a high in-line transmittance ~86.3% at 3.7 μm was fabricated. The refractive index ~1.7499 at 589.3 nm and absorption coefficient ~1.2 cm⁻¹ at 5 μm of MgAlON are between those of AlON and MgAl₂O₄ transparent ceramics, and Abbé number ~73.66 of MgAlON is the highest.     

A novel Nd3+-doped MgO-Al2O3-SiO2-based transparent glass-ceramics: Toward excellent fluorescence properties

Generally, glass-ceramics have superior properties compared to their parent glasses. Here, we prepared a novel Nd³⁺-doped MgO-Al₂O₃-SiO₂-based transparent glass-ceramics with excellent fluorescence properties. The effects of Nd₂O₃ content on the structure and properties of glass-ceramics were studied, aiming to provide a key guidance for preparing this transparent glass-ceramics. The results revealed that the glass stability increased originally and then decreased with increasing Nd₂O₃ content, so did the variation of wavenumbers in infrared spectra. And these glass-ceramics are mainly composed of cordierite with residual glassy phase. The three phenomenological intensity parameters (Ω_2,4,6) and radiative properties were estimated by Judd-Ofelt theory, and the values of Ω₂ first decreased and then increased with increasing Nd₂O₃ content. Three main emission peaks ascribed to the transitions from ⁴F_3/2 to ⁴I_9/2, ⁴I_11/2, ⁴I_13/2 at 898, 1057, 1330  nm were observed, respectively. The branching ratios for ⁴F_3/2→⁴I_11/2 transition increased as the Nd₂O₃ content raised, and the fluorescence lifetimes of the ⁴F_3/2 level were found to increase first and then decrease with Nd₂O₃ content (from 181 to 726 μs). The excellent fluorescence properties indicate that this novel glass-ceramics can be used as a potential solid-state optical functional material for 1.06 μm laser emission.