Impacts of substituting magnesium with zinc on crystallization behaviors in an aluminosilicate glass.

A series of zinc-magnesium mixed aluminosilicate glasses with the molar composition (1-r)MgO·rZnO·Al2O3·2.5SiO2, where r = 0.00, 0.25, 0.50, 0.65, 0.75, and 1.00, were fabricated to probe the effects of substitution of magnesium with zinc on crystallization behaviors. Based on the evolution of phase compositions as revealed by calorimetric behaviors and X-ray diffraction patterns, a series of transparent surface crystallized glasses ranging from high transparency for the pure Zn-end member to heavy translucency for the pure Mg-end member were fabricated through heat treatment at the first crystallization peak temperature for 20 min. With the substitution of Mg with Zn, the evolution of morphology unveiled by optical microscopy is ascribed to the alteration of crystal phases formed from the sole metastable Zn-ß quartz solid solution to the coexistence of polycrystal phases containing Zn-ß quartz solid solution, µ-cordierite, or α-cordierite. These findings are very helpful for optimizing the performance of crystallized aluminosilicate glasses.

Preparation of Ge-Sb-Se glass fibers with excellent bending properties by the pulsated orifice ejection method.

We have innovatively introduced the pulsated orifice ejection method into the preparation of glass fibers, successfully preparing high-purity Ge28Sb12Se60 glass fibers. These fibers have a smooth surface, uniform elemental distribution, and excellent bending properties, with a minimal bending radius of 2 mm. In the infrared spectrum from 2.5 to 13.5 µm, the fibers achieve 65% transmission. Additionally, the fibers possess a density of 4.586 g/cm3, a diameter of 35 µm, a glass transition temperature (Tg) of 369°C, and an onset crystallization temperature (Tx) of 557°C. We have also measured the surface tension of the glass fibers, finding values from 0.288 N/m to 0.124 N/m as temperatures rose from 450°C to 500°C. The POEM holds the potential to achieve fiber cores of lengths up to hundreds of meters in theory. Our work provides a distinctive perspective for the preparation of glass fibers.

Tuning the hardness and crack resistance through liquid-liquid phase separation in an aluminosilicate glass.

Here, spinodal decomposition is used as a strategy to enhance the mechanical properties of the 30Al2O3·70SiO2 glass. The melt-quenched 30Al2O3·70SiO2 glass exhibited a liquid-liquid phase separation with an interconnected snake-like nano-structure. Through further heat treatment at 850 °C for different durations of up to 40 hours, we observed a continuous increase of up to about 0.90 GPa in hardness (Hv) together with a drop in the slope for Hv rise at 4 hours. However, the crack resistance (CR) achieved a maximum value of 13.6 N when the heat treatment time was 2 hours. Detailed calorimetric, morphological and compositional analyses were conducted to elucidate the effect of tuning the thermal treatment time on hardness and crack resistance. These findings pave the way to utilize the spinodal phase-separated phenomena to enhance the mechanical properties of glasses.

Superhydrophobic Poly(l-lactic acid) Membranes with Fish-Scale Hierarchical Microstructures and Their Potential Application in Oil-Water Separation.

In this work, superhydrophobic poly(l-lactic acid) (PLLA) hierarchical membranes exhibiting excellent oil-removal performance, which is of great importance in curbing the oil-pollution environment, were fabricated by a simple solvent-evaporation-induced precipitation method. PLLA membranes with hierarchical micro/nanostructures (fish scales, fibrous sheets, and petal-like morphology) can be conveniently prepared by adjusting the preparation parameters including PLLA concentration, precipitation temperature, type of solvent and nonsolvent, and the addition of nano-SiO2. The results show that the water contact angle of the fish-scale-structured PLLA membrane was 138.6°, revealing that water repellency was significantly improved compared to that of the solvent-casting PLLA membrane (∼72.8°). Moreover, the PLLA/SiO2 nanocomposite membrane with a dense hierarchical micro/nanostructure had a water contact angle greater than 167.1°, which has great potential in oil-water separation.

Deformation mechanism of a metal-organic framework glass under indentation.

Revealing the deformation mechanism of brittle materials under sharp contact loading (indentation) is important for their applications since this knowledge is crucial for identifying the origin of flaw and scratch formation on their surfaces. As a newly emerged glass family, metal-organic framework (MOF) glasses have not been studied concerning the mechanism of their indentation-induced deformation. Here, we explore this mechanism for ZIF-62 glass (a typical MOF glass system). The fractions of densification and shear flow during indentation were determined by atomic force microscopy, while the elastic deformation was measured via nanoindentation. The results show that ZIF-62 glass deforms primarily through densification and elastic deformation under the sharp contact loading. Significant pile-ups around indents were not observed, indicating that no or limited shear flow occurs in the glass during indentation. This behavior could be attributed to three structural factors, namely, high free volume, easily densified glass structure, and limited translational mobility of structural units.

Mid-infrared supercontinuum generation in chalcogenide fibers with high laser damage threshold.

Laser damage thresholds (Ith) at 1.03 µm, as well as third-order nonlinear refractive indices (n2) and two photon absorption coefficients (ß) at 1.55 µm of a number of Ge-As-S glasses were measured and systematically studied. The glass with the composition Ge0.12As0.24S0.64 showed a high Ith and the maximum figure of merit (fm= n2/(ß·λ)), and therefore was selected as the core material for the fabrication of a step-index fiber. A compatible glass with the composition Ge0.18As0.1S0.72 was chosen as the cladding material. Based on the dispersion calculations, the fiber with a core diameter of ∼7-10 µm was designed. The designed fiber was fabricated by a multiple step rod-in-tube method. When the fiber with a core diameter of ∼9 µm and a length of ∼13.5 cm was pumped by ∼170 fs pulses (1 MHz) at 4.5 µm, the mid-infrared supercontinuum (SC) covering 1.3-8.1 µm was generated. These results demonstrate the good potential of Ge-As-S chalcogenide fibers for producing high-brightness broadband mid-infrared SC light sources.

Optical properties of a melt-quenched metal-organic framework glass.

Metal-organic framework (MOF) glasses are characterized by the possession of both inorganic and organic components, linked in a continuous network structure by coordination bonds. To the best of our knowledge, the optical properties of MOF glasses have not been reported until now. In this work, we prepared a transparent bubble-free bulk MOF glass, namely, the ZIF-62 glass (ZnIm2-xbImx), using our newly developed hot-pressing technique, and measured its optical properties. The ZIF-62 glass has a high transmittance (up to 90%) in the visible and near-infrared wavelength ranges, which is comparable to that of many oxide glasses. Using the Becke line nD method, we found that the ZIF-62 glass exhibits a refractive index (1.56) similar to most inorganic glasses, though a lower Abbe number (∼31).

Melt-Quenched Glasses of Metal-Organic Frameworks.

Crystalline solids dominate the field of metal-organic frameworks (MOFs), with access to the liquid and glass states of matter usually prohibited by relatively low temperatures of thermal decomposition. In this work, we give due consideration to framework chemistry and topology to expand the phenomenon of the melting of 3D MOFs, linking crystal chemistry to framework melting temperature and kinetic fragility of the glass-forming liquids. Here we show that melting temperatures can be lowered by altering the chemistry of the crystalline MOF state, which provides a route to facilitate the melting of other MOFs. The glasses formed upon vitrification are chemically and structurally distinct from the three other existing categories of melt-quenched glasses (inorganic nonmetallic, organic, and metallic), and retain the basic metal-ligand connectivity of crystalline MOFs, which connects their mechanical properties to their starting chemical composition. The transfer of functionality from crystal to glass points toward new routes to tunable, functional hybrid glasses.

A medium range order structural connection to the configurational heat capacity of borate-silicate mixed glasses.

It has been reported that the configurational heat capacity (C(p,conf)) first increases and then becomes saturated with increasing B2O3/SiO2 ratio in borate-silicate mixed glasses. Through Raman spectroscopy measurements, we have, in this work, found an implication for the intermediate range order (IRO) structural connection to the composition dependence of the C(p,conf) of borate-silicate mixed glasses. In the silica-rich compositions, the C(p,conf) rapidly increases with increasing B2O3 content. This is attributed to the increase of the content of the B-O-Si network units ([B2Si2O8](2-)) and 6-membered borate rings with 1 or 2 B(4). In the boron-rich compositions, the C(p,conf) is almost constant, independent of the increase in the B2O3/SiO2 ratio. This is likely attributed to the counteraction between the decrease of the fraction of two types of metaborate groups and the increase of the fraction of other borate superstructural units (particularly 6-membered borate rings). The overall results suggest that the glasses containing more types of superstructural units have a larger C(p,conf).

Extreme Flexibility in a Zeolitic Imidazolate Framework: Porous to Dense Phase Transition in Desolvated ZIF-4.

Desolvated zeolitic imidazolate framework ZIF-4(Zn) undergoes a discontinuous porous to dense phase transition on cooling through 140 K, with a 23 % contraction in unit cell volume. The structure of the non-porous, low temperature phase was determined from synchrotron X-ray powder diffraction data and its density was found to be slightly less than that of the densest ZIF phase, ZIF-zni. The mechanism of the phase transition involves a cooperative rotation of imidazolate linkers resulting in isotropic framework contraction and pore space minimization. DFT calculations established the energy of the new structure relative to those of the room temperature phase and ZIF-zni, while DSC measurements indicate the entropic stabilization of the porous room temperature phase at temperatures above 140 K.

High Refractive Index GRIN Lens for IR Optics.

Infrared gradient refractive index (GRIN) material lenses have attracted much attention due to their continuously varying refractive index as a function of spatial coordinates in the medium. Herein, a glass accumulation thermal diffusion method was used to fabricate a high refractive index GRIN lens. Six Ge17.2As17.2SexTe(65-x) (x = 10.5-16) glasses with good thermal stability and high refractive index (n@10 µm > 3.1) were selected for thermal diffusion. The refractive index span (∆n) of 0.12 was achieved in this GRIN lens. After thermal diffusion, the lens still had good transmittance (45%) in the range of 8-12 µm. Thermal imaging confirmed that this lens can be molded into the designed shape. The refractive index profile was indirectly characterized by the structure and composition changes. The structure and composition variation became linear with the increase in temperature from 260 °C to 270 °C for 12 h, indicating that the refractive index changed linearly along the axis. The GRIN lens with a high refractive index could find applications in infrared optical systems and infrared lenses for thermal imaging.

Pore-forming mechanisms and sodium-ion-storage performances in a porous Na3V2(PO4)3/C composite cathode.

Na3V2(PO4)3 (NVP) is regarded as one of the most promising cathode materials for sodium-ion batteries (SIBs). However, it suffers from a dense bulk structure and low intrinsic electronic conductivity, which lead to limited electrochemical performances. Herein, we propose a surfactant-assisted molding strategy to regulate the pore-forming process in NVP/C composite cathode materials. More precisely, the forming process of the pores in NVP could be easily controlled by utilizing the huge difference in critical micelle concentration of a surfactant (cetyltrimethylammonium bromide, CTAB) in water and ethanol. By reasonably modulating the ratio of water and ethanol in the solution, the as-synthesized NVP/C sample exhibited a three-dimensional interconnected structure with hierarchical micro/meso/macro-pores. Benefiting from these hierarchical porous structures in NVP/C, the structural stability, contact surface with the electrolyte, and electronic/ionic conductivity were improved simultaneously; whereby the optimized porous NVP/C sample exhibited an excellent high-rate performance (61.3 mA h g-1 at 10 C) and superior cycling stability (90.2% capacity retention after 500 cycles at 10 C).

The glass transition in the high-density amorphous Zn/Co-ZIF-4.

The high-density amorphous phases (HDAs) of bimetallic zeolitic imidazolate frameworks (Zn/Co-ZIF-4) were prepared. The temperature dependence of the isobaric heat capacity (Cp) of ZIF-4 HDAs was measured to determine the glass transition temperature (Tg) of HDAs. The Tg non-linearly decreases with the molar ratio R, where R is Co/(Co + Zn), indicating the presence of a mixed-metal node effect. This effect arises from the non-linear increase of the degree of configurational freedom in the HDA as R increases. The degree of configurational freedom is inversely correlated with the network connectivity, which is, in turn, affected by variations in the MN4 (M: Zn or Co; N: nitrogen) tetrahedral symmetry in the ZIF-4 HDA. Overall, this work offers valuable insights into the glass transition of metal-organic frameworks.

An Upper Bound Visualization of Design Trade-Offs in Adsorbent Materials for Gas Separations: CO2 , N2 , CH4 , H2 , O2 , Xe, Kr, and Ar Adsorbents.

The last 20 years have seen many publications investigating porous solids for gas adsorption and separation. The abundance of adsorbent materials (this work identifies 1608 materials for CO2 /N2 separation alone) provides a challenge to obtaining a comprehensive view of the field, identifying leading design strategies, and selecting materials for process modeling. In 2021, the empirical bound visualization technique was applied, analogous to the Robeson upper bound from membrane science, to alkane/alkene adsorbents. These bound visualizations reveal that adsorbent materials are limited by design trade-offs between capacity, selectivity, and heat of adsorption. The current work applies the bound visualization to adsorbents for a wider range of gas pairs, including CO2 , N2 , CH4 , H2 , Xe, O2 , and Kr. How this visual tool can identify leading materials and place new material discoveries in the context of the wider field is presented. The most promising current strategies for breaking design trade-offs are discussed, along with reproducibility of published adsorption literature, and the limitations of bound visualizations. It is hoped that this work inspires new materials that push the bounds of traditional trade-offs while also considering practical aspects critical to the use of materials on an industrial scale such as cost, stability, and sustainability.

Effect of Se on Structure and Electrical Properties of Ge-As-Te Glass.

The Ge-As-Te glass has a wide infrared transmission window range of 3-18 µm, but its crystallization tendency is severe due to the metallicity of the Te atom, which limits its development in the mid- and far-infrared fields. In this work, the Se element was introduced to stabilize the Ge-As-Te glass. Some glasses with ΔT ≥ 150 °C have excellent thermal stability, indicating these glasses can be prepared in large sizes for industrialization. The Ge-As-Se-Te (GAST) glasses still have a wide infrared transmission window (3-18 µm) and a high linear refractive index (3.2-3.6), indicating that the GAST glass is an ideal material for infrared optics. Raman spectra show that the main structural units for GAST glass are [GeTe4] tetrahedra, [AsTe3] pyramids, and [GeTe4Se4-x] tetrahedra, and with the decrease of Te content (≤50 mol%), As-As and Ge-Ge homopolar bonds appear in the glass due to the non-stoichiometric ratio. The conductivity σ of the studied GAST glasses decreases with the decrease of the Te content. The highest σ value of 1.55 × 10-5 S/cm is obtained in the glass with a high Te content. The activation energy Ea of the glass increases with the decrease of the Te content, indicating that the glass with a high Te content is more sensitive to temperature. This work provides a foundation for widening the application of GAST glass materials in the field of infrared optics.

Percolative Channels for Superionic Conduction in an Amorphous Conductor.

All-solid-state batteries greatly rely on high-performance solid electrolytes. However, the bottlenecks in solid electrolytes are their low ionic conductivity and stability. Here we report a new series of amorphous xAgI·(1-x)Ag3PS4 (x = 0∼0.8 with interval of 0.1) conductors, among which the sample with x = 0.8 exhibits the highest ionic conductivity (about 1.1 × 10-2 S cm-1) and ultrahigh chemical stability. We discovered the existence of mixed disordered Ag3PS4 and AgI clusters in the amorphous conductors using solid-state nuclear magnetic resonance spectroscopy. The high ionic conductivity was ascribed to the formation of the interconnecting AgI clusters, i.e., the percolative channels for superionic conduction. The composition dependence of the ionic conductivity for this series of amorphous conductors was clarified by a continuum percolation model. These findings provide fundamental guidance for designing and fabricating high-performance amorphous solid electrolytes for all-solid-state batteries.

High Verdet Constant Glass for Magnetic Field Sensors.

Due to the high transparency, high Verdet constant, as well as easy processing properties, rare-earth ion-doped glasses have demonstrated great potential in magneto-optical (MO) applications. However, the variation in the valence state of rare-earth ions (Tb3+ to Tb4+) resulted in the decreased effective concentration of the paramagnetic ions and thus degraded MO performance. Here, a strategy was proposed to inhibit the oxidation of Tb3+ into Tb4+ as well as improve the thermal stability by tuning the optical basicity of glass networks. Moreover, the depolymerization of the glass network was modulated to accommodate more Tb ions. Thus, a record high effective concentration (14.19 × 1021/cm3) of Tb ions in glass was achieved, generating a high Verdet constant of 113 rad/(T·m) at 650 nm. Lastly, the first application of MO glass for magnetic field sensors was demonstrated, achieving a sensitivity of 0.139 rad/T. We hope our work provides guidance for the fabrication of MO glass with high performance and thermal stability and could push MO glass one step further for magnetic sensing applications.

Second-order optical nonlinearity and ionic conductivity of nanocrystalline GeS2-Ga2S3-LiI glass-ceramics with improved thermo-mechanical properties.

IR-transparent chalcogenide glass-ceramics were fabricated through a careful ceramization process of the as-prepared 65 GeS(2) x 25 Ga(2)S(3) x 10 LiI glasses at a temperature of 403 degrees C for various durations. Owing to the precipitation of Li(x)Ga(y)S(z) crystals with a Ga(2)S(3)-like structure, clear second-harmonic generation was observed in the sample crystallized at 403 degrees C for 60 h, which has a greatly improved resistance to environmental impairment. Additionally, it is found that the shorter crystallization process (< or = 60 h) contributed to the enhancement of Li(+) ionic conductivity, whereas a longer heat-treatment (80 h) would impair that of the glass-ceramics. The micro-structural origin of these varied properties was elucidated in detail. The corresponding results will be of benefit for the optimization of designed transparent chalcogenide glass-ceramics with improved thermo-mechanical properties, a permanent second-order optical nonlinearity, or a well-enhanced ionic conductivity for application in amorphous solid electrolytes.

From Molten Calcium Aluminates through Phase Transitions to Cement Phases.

Crystalline calcium aluminates are a critical setting agent in cement. To date, few have explored the microscopic and dynamic mechanism of the transitions from molten aluminate liquids, through the supercooled state to glassy and crystalline phases, during cement clinker production. Herein, the first in situ measurements of viscosity and density are reported across all the principal molten phases, relevant to their eventual crystalline structures. Bulk atomistic computer simulations confirm that thermophysical properties scale with the evolution of network substructures interpenetrating melts on the nanoscale. It is demonstrated that the glass transition temperature (T g) follows the eutectic profile of the liquidus temperature (T m), coinciding with the melting zone in cement production. The viscosity has been uniquely charted over 14 decades for each calcium-aluminate phase, projecting and justifying the different temperature zones used in cement manufacture. The fragile-strong phase transitions are revealed across all supercooled phases coinciding with heterogeneous nucleation close to 1.2T g, where sintering and quenching occur in industrial-scale cement processing.

Origin of photo-induced transmitting oscillations in chalcogenide glasses.

Light-induced oscillatory behaviors of transmission in chalcogenide glasses are investigated using a continuous wave tunable Ti-sapphire laser. It is shown that phase change, thermal fluctuation, nonlinear index change and periodic self focusing are not at the origin of light-induced oscillatory transmittance in chalcogenide glasses. Instead, results indicate that the interference of transmitting and reflecting light is at the origin of the oscillatory behaviors of transmitted light. Just like the principle of Fabry-Pérot interferometer, these interferences result in a periodic change in transmission as the related interferential beams get in and out of phase. However, this transmitting oscillatory behavior can be registered by the detector only when the change of optical path length difference initiated by photo-induced effects is slower enough compared with the corresponding response time of the detector. Several photo-structural effects contribute to that phenomenon including photo-expansion, photo-darkening, and permanent self focusing. It appears that fluctuations of the light source intensity induce a wide distribution of the oscillatory periods.