Precipitation Of Nanocrystals Research Articles

Increased tensile strength induced by the precipitation of nanocrystals for welding joints of Zr-based amorphous alloys

Zr-based amorphous alloys have attracted intensive attention for applications because of their excellent mechanical property. However, the welding process is inevitable for some special cases, such as the obtain of large size structure parts. It is significant to clarify the influence of introduced welding joints on mechanical properties in Zr-based amorphous alloys. Herein, the increased tensile strength of welding joints in Zr-based amorphous alloys is demonstrated by choosing a suitable initial temperature of Cu cooling fixtures for pulsed laser welding. It is found that an optimized tensile strength is observed when the initial temperature is −20 °C. With the decrease of the initial temperature from 10 to −30 °C, the tensile strength shows a trend of first increasing and then decreasing. Combined with the characterization of microstructures, it can be concluded that the increased tensile strength results from the precipitation of nanocrystals in the heat affected zone. Thus, our results provide a method to improve the mechanical property by controlling the microstructures of the heat affected zone in welding joints of Zr-based amorphous alloys.

Dual-phase coexistence enables to alleviate resistance drift in phase-change films

The amorphous phase-change materials with spontaneous structural relaxation leads to the resistance drift with the time for phase-change neuron synaptic devices. Here, we modify the phase change properties of the conventional Ge2Sb2Te5 (GST) material by introducing an SnS phase. It is found that the resistance drift coefficient of SnS-doped GST was decreased from 0.06 to 0.01. It can be proposed that the origin originates from the precipitation of GST nanocrystals accompanied by the precipitation of SnS crystals compared to single-phase GST compound systems. We also found that the decrease in resistance drift can be attributed to the narrowed bandgap from 0.65 to 0.43 eV after SnS-doping. Thus, this study reveals the quantitative relationship between the resistance drift and the band gap and proposes a new idea for alleviating the resistance drift by composition optimization, which is of great significance for finding a promising phase change material.

Z-scan of ITO nanocrystals grown inside glass.

Indium tin oxide (ITO) nanocrystals 1-10 nm in size were grown via thermal treatment of a boroaluminosilicate parent glass. The nonlinear behavior of the obtained glass-ceramic was investigated with the Z-scan technique using 550 ps pulses of a 532 nm source at a 500 Hz repetition rate. The nonlinear response was rich, with the sample exhibiting third- and fifth-order nonlinearities as well as saturable absorption and two-photon absorption (TPA), depending on the locale probed. Photoinduced changes were also observed, with high intensity exposures yielding an increased magnitude of the response when lower power trials were subsequently repeated at the same sample position. The work demonstrates that ITO nanocrystal precipitation in bulk glass yields effective nonlinear response and suggests that with further development may enable more compact devices exploiting ITO and the need for particle deposition routes.

Accurate identification of glass crystallization helps in selecting high electronic conductivity materials

Though the current research on vanadium-based glass electrodes has made great progress, the conductivity theory of V-based glasses has not been obviously improved and crystals cannot be positioned precisely. The changes in the valence state of V3+, V4+ and V5+ are regulated by the strong reducing agent Fe2P to realize valence bond transformation of the amorphous electrode, explore the redox process of multi-electron reactions and further optimize the conductivity of electrode materials. VPFe2 and VPFe3 precipitate VO2 crystals and VPFe4 precipitates VO2 and V6O11 crystals. Electron back-scattered diffraction was used to accurately identify the distribution and specific positions of both types of crystals. V6O11 crystals exhibit a strong texture according to pole figure and inverse pole figure. XPS reveals that Fe2P and V2O5, undergo a redox reaction during the high-temperature melting process, where V5+ is reduced to V4+ and V3+ and V4+ renders a positive influence on conductivity. The addition of Fe2P increases the content of V4+ in the glass and VPFe3 glass contains the highest content of V4+, leading to the highest electronic conductivity. V2O5 transforms into VO2 crystals and VO2 transforms into V6O11 with the increase of Fe2P content. The type of nanocrystal precipitation in glass affects electronic conductivity.

Effect of CsCl nanocrystallization on the acousto-optic properties of GeS2-Sb2S3-CsCl chalcogenide glass-ceramics

Crystallization of chalcogenide glasses provides a new possibility to decoupling the trade-off between acousto-optic figure of merit (M2) and acoustic attenuation (α) properties of acousto-optic materials. In this work, 62.5GeS2-12.5Sb2S3-25CsCl chalcogenide glasses ceramics were prepared, and CsCl nanocrystals were precipitated and evidenced by using scanning electron microscopy and X-ray diffractometer. The precipitation of CsCl nanocrystals led to a 10 % decrease in M2 from 113.85 to 102.08 × 10−18 s3/g, but also to a substantial improvement in α, which decreased by 38 % from 3.28 to 2.03 dB/cm. The glass crystallization that together with a rearrangement of the glass network structure would result in the enhancement of network rigidity of the residual glass matrix, thus contributing to the reduction of acoustic attenuation.

Tailoring fluoride networks to precipitate hexagonal Ln1-yMyF3-y nanocrystals in glass: Towards short-wavelength upconversion PL of lanthanides

The AlF3-MF2-LnF3 (M = Ca; Sr; Ba; Ln = Yb/Tm) based pure fluoride GCs are essentially ideal candidates for the realization of PL in UV and VIS spectral region. However, the pure fluoride glasses are prone to precipitation of undesired nano-crystals while quenching and post annealing due to their poor chemical stability. Therefore, the development of such glass systems requires strict adherence to composition control right from the outset. This research employed extensive molecular dynamics (MD) simulations and incorporated the results into the experimental design to develop an efficient multicomponent fluoride glass system. Vivid simulation of M-F-Ln and M-F-Al nano-cluster formation via MD are observed in the glass matrix. These nano-clusters serve as the structural origins of the precipitated nano-crystals in GCs post heat treatment. Through meticulous manipulation of the Al/M ratio, it became feasible to theoretically forecast the transformation of the glass matrix from a cubic M1-xLnxF2+x to a hexagonal Ln1-yMyF3-y nano-crystal precipitated GCs, which could conceivably be manufactured experimentally. This transformation offers superior luminescent performance for Ln1-yMyF3-y containing GCs enabling short-wavelength PL realisation in near UV (∼361 nm with 8-fold enhancement) and VIS (∼478 nm with 1.7-fold enhancement) from Yb3+/Tm3+ transitions, in comparison to its cubic M1-xLnxF2+x counterpart. Hence, we propose an effective fluoride glass system for short-wavelength upconversion luminescent applications through the integration of MD simulations and experimental research.

Redox process and lithiation mechanism of amorphous vanadium-silicon materials as lithium-ion battery anode

V2O5-TeO2 (VT) is a vanadium-based amorphous lithium-ion battery (LIB) anode material that exhibits a high specific energy, but its low-capacity retention rate and low conductivity limit its widespread application. Different amounts of Si were introduced into VT anode materials to increase their initial discharge capacity and conductivity, which regulated the vanadium redox reaction. 67 V2O5-30TeO2-3Si (VTS3) exhibited the highest conductivity and V4+ content (49.8%). When the Si content was increased, the V4+ content decreased, indicating that Si successfully regulated the redox reaction. The results showed that VTS3 had a high initial discharge capacity of 1187.3 mAh g−1, while that of VT was only 906.5 mAh g−1. After 50 charge-discharge cycles, the retention rates of VT and VTS3 were 15.6% and 25.0%, respectively. After cycling, the precipitation of nanocrystals, especially LiV2O5, from the glass matrix improved the capacity retention of VTS3 by enhancing reversible lithium insertion. The synergy of this disordered-ordered transition improved the discharge capacity and reversibility. Density functional theory (DFT) calculations showed that due to the substitution of Si, the gap between Highest Occupied Molecular Orbital (HOMO) and HOMO-1 was shortened, Li-O electron aggregation was enhanced, the structure was improved, and electronic conductivity was enhanced. At the same time, sufficient Si content increased the initial specific capacity but reduced the retention rate, which was because the volume expansion during the charge-discharge cycle reduced the number of active sites. This work offers a new strategy for preparing LIB electrode materials by introducing Si to regulate redox reactions and precipitate nanocrystals.

Investigation on gallium doping Ge-As-S chalcogenide glass and glass ceramics

In this work, bulk chalcogenide glasses (Ge35As10S55)100-xGax (x = 0,1,3,5,7,9) were prepared using the traditional melt quenching method, and glass ceramics were prepared to improve the mechanical properties through heat treatment. Optical, thermal and mechanical properties of the glass and glass ceramic samples were measured by FTIR, DSC and Vickers hardness analysis. Results indicate that glass samples exhibited about 70% IR-transmission around 3–12 µm. The hardness of these pure glasses increased from 231 to 282 kgf/mm2 through gallium doping and improvement of melt-quenching conditions. The type of nanocrystals precipitated in the glass ceramics were characterized by XRD. Existence of a γ-Ga2S3 crystal phase enhanced the hardness of the glass. Also, the size and distribution of nanocrystals in the microstructure of the glass ceramics were investigated by SEM. The hardness of (Ge35As10S55)93Ga7 glass reached to 302.6 kgf/mm2 by precipitation of nanocrystals with diameter smaller than 500 nm.

Influence of Mo/V coupled multi-electron reactions and the crystalline phase transition of VO2 on high specific capacity of lithium-ion batteries

To further improve the specific capacity and stability of amorphous vanadium-based lithium-ion battery cathode materials, MoS2 was introduced for the first time into the 70V2O5–30Li3PO4 (VP) glass cathode system. Both Mo and S participated in the redox reaction, achieving for the first time an increase in the V4+ content from 21.8% to 50.4%. This improved the electrical conductivity. Moreover, the realization of a Mo/V multi-electron coupling reaction promoted the capacity. The precipitation of LiV2O5 and MoP2O8 nanocrystals during electrocycling enhanced the cycling stability and reaction kinetics. Compared to VP, the capacity of 67V2O5–30Li3PO4–3MoS2 (VPMo3) was enhanced by more than 50% at a current density of 100 mA g-1, and the capacity retention after 50 cycles was improved by about 20%. Notably, the VO2 nanocrystals precipitated during the melt preparation underwent a metal-insulator phase transition (MIT), and their structural transformation affected conductivity.

Nd-doped CsPbBr3 borosilicate glass ceramics: Crystallization behavior and photoluminescence kinetics

Rare-earth (RE) doping is one of the valid approaches to optimize the optical performance of the CsPbBr3 perovskite quantum dot glass. Thus, the research on the crystallization behavior of RE ions doped CsPbBr3 borosilicate glass and the energy transformation mechanism between the RE ions and CsPbBr3 is significant for the development of advanced Ln-doped perovskite glass materials. In this work, CsPbBr3 borosilicate glass ceramics doped with different concentrations of Nd2O3 were successfully synthesized. It was found that Nd2O3 makes the glass network structure more compact and then inhibits the precipitation of CsPbBr3 nanocrystals. Additionally, there is energy transfer between Nd3+ and CsPbBr3, which quenches the photoluminescence of CsPbBr3 borosilicate glass. This work deepens the understanding of the structural and photophysical properties of Ln-doped CsPbBr3 borosilicate glass ceramics and provides a reference value for the related work of RE ions doped perovskite borosilicate glass.

Bright Transparent Scintillators with High Fraction BaCl2 : Eu2+ Nanocrystals Precipitation: An Ionic-Covalent Hybrid Network Strategy toward Superior X-Ray Imaging Glass-Ceramics.

Metal halide crystals are bright but hygroscopic scintillator materials that are widely used in X-ray imaging and detectors. Precipitating them in situ in glass to form glass ceramics (GCs) scintillator offers an efficient avenue for large-scale preparation, high spatial resolution, and excellent stability. However, precipitating a high fraction of metal halide nanocrystals in glass to maintain high light yield remains a challenge. Herein, an ionic-covalent hybrid network strategy for constructing GCs scintillator with high crystallinity (up to ≈37%) of BaCl2 : Eu2+ nanocrystals is presented. Experimental data and simulations of glass structure reveal that the Ba2+ -Cl- clustering promotes the high crystallization of BaCl2 nanocrystals. The ultralow phonon energy (≈200 cm-1 ) of BaCl2 nanocrystals and good Eu reduction effect enable high photoluminescence inter quantum efficiency (≈80.41%) in GC. GCs with varied crystallinity of BaCl2 : Eu2+ nanocrystals demonstrate efficient radioluminescence and tunable scintillator performance. They either outperform Bi4 Ge3 O14 single crystal by over 132% steady-state light yield or provide impressive X-ray imaging resolutions of 20 lp mm-1 . These findings provide a new design strategy for developing bright transparent GCs scintillators with a high fraction of metal halide nanocrystals for X-ray high-resolution imaging applications.

Monovalent Charge Compensation Enables Efficient Lanthanide‐Based Near‐Infrared Perovskite LEDs

AbstractLanthanide ions (Yb3+ or Er3+) alloying of CsPb(Cl1‐xBrx)3 quantum dots (QDs) to emit approaching 1000 nm show promise in near‐infrared light‐emitting diodes (NIR‐LEDs). High Yb3+ alloying ratio increases the electroluminance efficiency of emission at 990 nm and enables high external quantum efficiency (EQE) of NIR‐LEDs, however, the high alloying ratio also results in inferior material stability and PLQY drop because of Yb3+‐induced nanocrystal precipitation. This study finds that the heavy alloying of Yb3+ ions causes lattice distortion and coherent energy reduction of Yb3+: CsPb(Cl1‐xBrx)3 QDs, induced by two Yb3+ ions replacing three Pb2+, which leads to the collapse of the octahedral structure in ambient conditions. It posits that spontaneous monovalent ion (Na+) alloying can address the trade‐off between material stability and emission intensity. The Na+ occupies the vacancy of Pb2+ ions, relaxing the distortion in the lattice and improving the phase stability of octahedral structure, and this optimized structure in turn allows a higher Yb3+ alloying ratio. Stability measurements show that the Na+/Yb3+ co‐alloyed films show ten‐fold higher material stability and 2.0‐fold emission efficiency related to controls. It reports that as a result Na+/Yb3+ co‐alloyed NIR‐LEDs have an EQE of 6.4% at 990 nm, which is among the highest perovskite NIR‐LEDs beyond 950 nm.

Uranium photo-precipitation coupled with fulvic acid oxidation under anoxic and oxic conditions

Uranium (U) is of vital importance for the nuclear power industry. Its mining, processing and disposal impose significant risks to the environment. Precipitation and fate of uranium in water bodies are of interest for environmental protection. In this work, we propose that fulvic acid (FA), a natural organic matter, can photo-precipitate ∼ 93.2% U under anoxic conditions within 3 h and ∼ 88.3% under oxic conditions within 48 h, respectively. Based on HRTEM, SAED and XPS analyses of the anoxic precipitate, U2O5 and UO2(OH)2 nanocrystals precipitate with FA and its decomposition intermediates. XPS analysis of C1s of the anoxic precipitate further reveals that FA is partly oxidized and has lost its conjugated benzoic ring and aldehyde groups, forming more carboxylic groups. On the other hand, XRD and XPS analyses on the oxic precipitate indicates the formation of UIV(C2O4)2·2H2O and UVIO3·0.75CO2·0.68H2O, demonstrating much deeper oxidation of FA under oxic conditions. In contrast to numerous previous studies focusing on heterogeneous photocatalytic reduction of U using solid catalyst, the uranium removal technique here spared the cost of catalyst synthesis, the necessity of sacrificer for uranium photo-reduction and U retrieval from the catalyst’s surface. The results also shine a light on new pathways for uranium fates in uranium-bearing water bodies such as rivers and lakes.

Highly Luminescent Rb-Doped Cs4PbBr6 Nanocrystals in Borogermanate Glass

For the first time, the synthesis, luminescent and structural properties of stable perovskite-type (Cs1−xRbx)4PbBr6 (R = Cs, Rb) nanocrystals are shown. In the absence of rubidium, Cs4PbBr6 and CsPbBr3 perovskite crystals precipitate in the ZnO–Na2O–B2O3–GeO2 glass matrix. With ascending rubidium content, the precipitation of (Cs,Rb)4PbBr6 nanocrystals is replaced by the Rb4PbBr6 nanocrystals nucleation. Nucleated nanocrystals exhibit an intense green luminescence. With an increase of the rubidium content, the luminescence maximum shifts to the blue region, the luminescence quantum yield increases from 28 to 51%, and the average decay time increases from 2 to 8 ns. Several assumptions have been made about the nature of the green luminescence of perovskite-like Cs4PbBr6 and (Cs,Rb)4PbBr6 crystals in glasses. It is concluded that the most probable cause is the impurity inclusions of CsPbBr3 and (Cs,Rb)PbBr3 crystals.

Crystallization Mechanism of Gel-Derived SiO2–TiO2 Amorphous Nanobeads Elucidated by High-Temperature In Situ Experiments

SiO2–TiO2 amorphous nanobeads with a TiO2 content up to 50 mol % were synthesized by sol–gel spray drying. Their crystallization during heat treatments was then characterized by in situ high-temperature techniques including X-ray diffraction, Raman spectroscopy, and particularly high-resolution transmission electron microscopy. Intrinsic nanoscale chemical modulations could be identified already in the as-prepared nanobeads and were shown to play a major role for the nonisochemical precipitation of TiO2 nanocrystals during heating experiments: the size and compositional contrast of such fluctuations progressively evolved and increased until the emergence of long-range ordering. The formation of TiO2 polymorphs occurred according to Ostwald’s rule of stages, with the metastable TiO2(B) phase acting as a precursor to stabilize anatase and rutile. The temporary appearance of TiO2(B) nanocrystals at early annealing stages was interpreted as the first direct experimental observation of subcritical crystalline nuclei.

Photophysical and temperature dependent analysis of Sm activated LiAlSi3O8 nanophosphor

Herein, we report the synthesis of nanosized LiAlSi3O8 phosphors; and investigate the structural and spectroscopic properties of Sm3+ ions doped in LiAlSi3O8 matrix. The development of nanosized phosphor is established by e-beam images and x-ray diffraction analysis which reveals precipitation of LiAlSi3O8 nanocrystals having crystalline size 35 ± 1 nm. Photoexcitation and luminescence analysis reveals the bright emission in the orange-red region under UV-blue excitations. The optimum luminescence intensity was observed at 602 nm (4G5/2 → 6H7/2) for 0.75 mol% concentration. The effect of concentration and laser excitation power on the emission characteristics of the Sm ion is also reported. The temperature-dependent optical analysis was carried out in the range 273–498 K temperatures. The variation in emission profile and the peak ratio reveals the good temperature sensitivity of the phosphor. The CIE coordinate analysis reveals the variation of colour perception with laser power, concentration, and temperature.

One-Step Crystallization of Gahnite Glass-Ceramics in a Wide Thermal Gradient

The glass crystallization regime plays a crucial role in the fabrication of glass ceramics: it affects both phase composition and microstructure, and thus the properties of the final product. In the search for new glass-ceramic materials, the development of a proper heat-treatment schedule involves the utilization of numerous glass samples that need to be thermally treated and then investigated to determine the values of the target characteristics. In this study, we evaluated the effect of crystallization temperature on the glass structure, phase composition, and hardness of glass ceramics in the ZnO-MgO-Al2O3-SiO2 system containing TiO2 and ZrO2 as nucleators. To maximize the number of heat treatments, we performed polythermal crystallization of the glass in a wide temperature range with the help of a gradient furnace. Using X-ray diffraction, Raman spectroscopy, and transmission electron microscopy, we showed the precipitation of gahnite nanocrystals as the main phase in the bulk of a single glass sample and observed a gradual change in its microstructure, transparency, and hardness. The dependence of Vickers hardness values on heat treatment temperature was found to follow a non-linear trend, revealing the optimal thermal range for glass crystallization.

Enhanced optical and electrical properties of narrow-bandgap cerium borate glasses and nanostructured glass-ceramics: influence of V2O5-incorporation

Improvement of optical and electrical properties of borate glasses is a great demand for upgrading optoelectronic devices. Additionally, the transformation of borate glasses to nanostructured glass-ceramics endows them with outstanding beneficial properties to widen their application range. Herein, novel borate glass compositions are synthesized by the facile melt quenching method. The influences of V2O5-incorporation and nanocrystallization on the structural, optical, and electrical properties of the investigated cerium borate glasses are studied. The heat-treatment process promotes the precipitation of CeO2 and VCeO4 nanocrystals in the glass network. Linear and high dependence of the band gap of the as-prepared glasses on the V2O5 concentration is observed. A narrow band gap (about 1.6), which lies in the range of ideal bandgaps for two-junction photovoltaic cell applications, is achieved. Strong absorption in the visible and/or UV regions is attained for the studied samples, which is beneficial to shield laser emissions (up to 794 nm) and/or protect against the hazard of UV radiation. High DC conductivity (about 3 × 10−6 S m−1) is approved for the glass sample containing V2O5 content of 10 mol%. The investigated glasses and nanostructured glass-ceramics are recommended as promising candidates for UV-protection Sunglasses, laser safety, visible light irradiation photocatalyst, and next-generation semiconductors.

Investigation of gallium and tin on IG5 commercial chalcogenide glass and glass ceramics

In this research, optical, mechanical, and thermal properties of chalcogenide glasses in a Se-Ge-Sb system were studied with 1, 3, 5, 7, and 9 % Gallium and tin. Glass samples melted at 850 °C for 20 h were quenched in the melted salt. XRD analyses were performed for them. The properties of this ternary system compared in presence of two different additive. The aim of this study was to improve the mechanical properties of the Se60Sb12Ge28 chalcogenide glass (IG5) with the thermal treatment and prepare glass ceramics with high strength and IR transmittance. The glasses exhibited about 70 % IR-transmission around 2–17 µm with the weakest peaks. The hardness of these pure glasses increased by adding the Gallium and improvement of the melting conditions and quenching so that it reached ∼ 230–345 Kg.mm2. This high hardness was firstly reported for chalcogenide glasses. Appropriate temperature and time were selected to precipitate sub-micron nanocrystals and prepare ceramic glasses, heat treatment was also performed. The size and distribution of nanocrystals in the glass ceramic microstructure was investigated by Fe-SEM and TEM. The hardness of this ceramic glass reached to ∼ 280–370 MPa by precipitation of nanocrystals with diameter of 100–400 nm.

Weak Electron–Phonon Coupling and Enhanced Thermoelectric Performance in n‐type PbTe–Cu2Se via Dynamic Phase Conversion

AbstractThis study investigates Ga‐doped n‐type PbTe thermoelectric materials and the dynamic phase conversion process of the second phases via Cu2Se alloying. Introducing Cu2Se enhances its electrical transport properties while reducing its lattice thermal conductivity (κlat) via weak electron–phonon coupling. Cu2Te and CuGa(Te/Se)2 (tetragonal phase) nanocrystals precipitate during the alloying process, resulting in Te vacancies and interstitial Cu in the PbTe matrix. At room temperature, Te vacancies and interstitial Cu atoms serve as n‐type dopants, increasing the carrier concentration and electrical conductivity from ≈1.18 × 1019 cm−3 and ≈1870 S cm−1 to ≈2.26 × 1019 cm−3 and ≈3029 S cm−1, respectively. With increasing temperature, the sample exhibits a dynamic change in Cu2Te content and the generation of a new phase of CuGa(Te/Se)2 (cubic phase), strengthening the phonon scattering and obtaining an ultralow κlat. Pb0.975Ga0.025Te‐3%CuSe exhibits a maximum figure of merit of ≈1.63 at 823 K, making it promising for intermediate‐temperature device applications.