In Situ Kinetic Observations on Crystal Nucleation and Growth

Understanding the nanoscale phenomena of nucleation and crystal growth in electrodeposition

Electrodeposition is used at the industrial scale to make coatings, membranes, and composites. With better understanding of the nanoscale phenomena associated with the early stage of the process, electrodeposition has potential to be adopted by manufacturers of energy storage devices, advanced electrode materials, fuel cells, carbon dioxide capturing technologies, and advanced sensing electronics. The ability to conduct precise electrochemical measurements using cyclic voltammetry, chronoamperometry, and chronopotentiometry in addition to control of precursor composition and concentration makes electrocrystallization an attractive method to investigate nucleation and early-stage crystal growth. In this article, we review recent findings of nucleation and crystal growth behaviors at the nanoscale, paying close attention to those that deviate from the classical theories in various electrodeposition systems. The review affirms electrodeposition as a valuable method both for gaining new insights into nucleation and crystallization on surfaces and as a low-cost scalable technology for the manufacturing of advanced materials and devices.

Preparation of Near-Spherical α-Al2O3 Particles by Enhanced Precipitation of Gibbsite from Sodium Aluminate Solution Using Highly Dispersed Al2O3 as Seeds

The near-spherical α-Al2O3 particles (∼200 nm) were prepared for the first time through the precipitation of gibbsite from a supersaturated sodium aluminate solution, with the addition of an acidic solution containing highly dispersed nanosized Al2O3 seeds. The near-spherical α-Al2O3 were achieved by employing seeds at 1100 °C, with the initial nucleation temperature being only 900 °C, due to the highly homogeneous dispersion of the seeds into gibbsite formation by in situ growth that can effectively enhance the role of the seeds in the phase transition. Moreover, the precipitation rate of sodium aluminate solution was significantly accelerated by 17-fold. This acceleration was due to the slightly acidic solution breaking the stability of sodium aluminate solution through a neutralization reaction on the seed surface, leading to the rapid formation of gibbsite nuclei on the seed surface. Our findings provide a feasible approach for the fabrication of well-dispersed α-Al2O3 particles and make the industrial production of well-dispersed α-Al2O3 from sodium aluminate solution a commercial reality.

Pb6Ba3Si2S8I10: a new thiohalide with a quasi-two-dimensional structure and wide band gap

Pb-based chalcogenides display abundant structural diversity and distinguished properties. Based on a mixed anion and dimensional reduction combined strategy, a wide band gap Pb-based thiohalide, Pb6Ba3Si2S8I10, has been rationally designed and synthesized experimentally by the flux method. The compound crystallizes in the R3̄c space group with cell parameters a = 9.7925(2) Å, b = 9.7925(2) Å, and c = 70.628(3) Å and is composed of [SiS4] tetrahedra and unprecedented [PbI5S2] polyhedral units, resulting in a unique quasi-two-dimensional structure, which enriches the chemical and structural diversity of Pb-based thiohalides. The experimental band gap of Pb6Ba3Si2S8I10 was determined to be 2.80 eV. Based on statistical analyses and to the best of our knowledge, it is the largest experimental optical band gap among the known Pb-based thiohalides. The results demonstrate the feasibility of using highly electropositive Ba atoms to regulate the dimensions of the structural framework of thiohalides and give new insights into the structure and property modifications of thiohalides by the mixed anion and dimensional reduction combined strategy.

Unveiling the Dynamic Pathways of Metal-Organic Framework Crystallization and Nanoparticle Incorporation for Li-S Batteries

Metal-organic frameworks (MOFs) present diverse building blocks for high-performance materials across industries, yet their crystallization mechanisms remain incompletely understood due to gaps in nucleation and growth knowledge. In this study, MOF structural evolution is probed using in situ liquid phase transmission electron microscopy (TEM) and cryo-TEM, unveiling a blend of classical and nonclassical pathways involving liquid-liquid phase separation, particle attachment-coalescence, and surface layer deposition. Additionally, ultrafast high-temperature sintering (UHS) is employed to dope ultrasmall Cobalt nanoparticles (Co NPs) uniformly within nitrogen-doped hard carbon nanocages confirmed by 3D electron tomography. Lithium-sulfur battery tests demonstrate the nanocage-Co NP structure's exceptional capacity and cycling stability, attributed to Co NP catalytic effects due to its small size, uniform dispersion, and nanocage confinement. The findings propose a holistic framework for MOF crystallization understanding and Co NP tunability through ultrafast sintering, promising advancements in materials science and informing future MOF synthesis strategies and applications.

Epitaxial Growth of Two-Dimensional Organic Crystals with In-Plane Heterostructured Domain Regulation

Complex organic lateral heterostructures (OLHs) with spatial distribution of two or more chemical components are crucial for designing and realizing unique structure-dependent optoelectronic applications. However, the precise design of well-defined OLHs with flexible domain regulation remains a considerable challenge. Herein, we present a stepwise solution self-assembly method to synthesize two-dimensional (2D) OLHs with a central rhombus domain and a lateral region featuring tunable blue and green emission based on the sequential nucleation and growth of 2D crystals. By controlling the initial crystallization time of 2,6-diphenylanthracene, the rhombic length ratio (α) of the multicolor-emissive part of the 2D OLHs is precisely modified. Furthermore, a third lateral layer is constructed on the resulting OLHs, demonstrating scalable lateral regulation. Significantly, these prepared 2D OLHs exhibit great excitation position-dependent waveguide characteristics and enable a 0.06 dB/μm low-loss waveguiding, which are conducive to photon transport and conversion for photonic integrated circuits. This work provides a stepwise strategy for the accurate fabrication of 2D OLHs, fabricating the developments of next-generation optoelectronics devices.

Solvent Dependence of Ionic Liquid-Based Pt Nanoparticle Synthesis: Machine Learning-Aided In-Line Monitoring in a Flow Reactor

Colloidal platinum nanoparticles (Pt NPs) possess a myriad of technologically relevant applications. A potentially sustainable route to synthesize Pt NPs is via polyol reduction in ionic liquid (IL) solvents; however, the development of this synthetic method is limited by the fact that reaction kinetics have not been investigated. In-line analysis in a flow reactor is an appealing approach to obtain such kinetic data; unfortunately, the optical featurelessness of Pt NPs in the visible spectrum complicates the direct analysis of flow chemistry products via ultraviolet-visible (UV-vis) spectrophotometry. Here, we report a machine learning (ML)-based approach to analyze in-line UV-vis spectrophotometric data to determine Pt NP product concentrations. Using a benchtop flow reactor with ML-interpreted in-line analysis, we were able to investigate NP yield as a function of residence time for two IL solvents: 1-butyl-1-methylpyrrolidinium triflate (BMPYRR-OTf) and 1-butyl-2-methylpyridinium triflate (BMPY-OTf). While these solvents are structurally similar, the polyol reduction shows radically different yields of Pt NPs depending on which solvent is used. The approach presented here will help develop an understanding of how the subtle differences in the molecular structures of these solvents lead to distinct reaction behavior. The accuracy of the ML prediction was validated by particle size analysis and the error was found to be as low as 4%. This approach is generalizable and has the potential to provide information on various reaction outcomes stemming from solvent effects, for example, differential yields, orders of reaction, rate coefficients, NP sizes, etc.

Regioselective epitaxial growth of metallic heterostructures

Constructing regioselective architectures in heterostructures is important for many applications; however, the targeted design of regioselective architectures is challenging due to the sophisticated processes, impurity pollution and an unclear growth mechanism. Here we successfully realized a one-pot kinetically controlled synthetic framework for constructing regioselective architectures in metallic heterostructures. The key objective was to simultaneously consider the reduction rates of metal precursors and the lattice matching relationship at heterogeneous interfaces. More importantly, this synthetic method also provided phase- and morphology-independent behaviours as foundations for choosing substrate materials, including phase regulation from Pd20Sb7 hexagonal nanoplates (HPs) to Pd8Sb3 HPs, and morphology regulation from Pd20Sb7 HPs to Pd20Sb7 rhombohedra and Pd20Sb7 nanoparticles. Consequently, the activity of regioselective epitaxially grown Pt on Pd20Sb7 HPs was greatly enhanced towards the ethanol oxidation reaction; its activity was 57 times greater than that of commercial Pt/C, and the catalyst showed increased stability (decreasing by 16.3% after 2,000 cycles) and selectivity (72.4%) compared with those of commercial Pt/C (56.0%, 18.2%). This work paves the way for the design of unconventional well-defined heterostructures for use in various applications.

Tailored Design of Mesoporous Nanospheres with High Entropic Alloy Sites for Efficient Redox Electrocatalysis

High Entropy Alloys (HEAs) are a versatile material with unique properties, tailored for various applications. They enable pH-sensitive electrocatalytic transformations like hydrogen evolution reaction (HER) and hydrogen oxidation reactions (HOR) in alkaline media. Mesoporous nanostructures with high surface area are preferred for these electrochemical reactions, but designing mesoporous HEA sis challenging. To overcome this challenge, a low-temperature triblock copolymer-assisted wet-chemical approach is developed to produce mesoporous HEA nanospheres composed of PtPdRuMoNi systems with sufficient entropic mixing. Owing to active sites with inherent entropic effect, mesoporous features, and increased accessibility, optimized HEA nanospheres promote strong HER/HOR performance in alkaline medium. At 30 mV nominal overpotential, it exhibits a mass activity of ≈167 (HER) and 151 A gPt -1 (HOR), far exceeding commercial Pt-C electrocatalysts (34 and 48 A gPt -1) and many recently reported various alloys. The Mott-Schottky analysis reveals HEA nanospheres inherit high charge carrier density, positive flat band potential, and smaller charge transfer barrier, resulting in better activity and faster kinetics. This micelle-assisted synthetic enable the exploration of the compositional and configurational spaces of HEAs at relatively low temperature, while simultaneously facilitating the introduction of mesoporous nanostructures for a wide range of catalytic applications.

Unveiling the Factors Influencing Different Nucleation Pathways and Liquid-Liquid Phase Separation

Exploring nucleation pathways has been a research hot spot in the fields of crystal engineering. In this work, vanillin as a model compound was utilized to explore the factors influencing different nucleation pathways with or without liquid-liquid phase separation (LLPS). A thermodynamic phase diagram of vanillin in the mixed solvent system of water and acetone from 10 to 55 °C was determined. It was found that the occurrence of LLPS might be related to different nucleation pathways. Under the guidance of a thermodynamic phase diagram, Raman spectroscopy and molecular simulation were applied to investigate the influencing factors of different nucleation paths. It was found that the degree of solvation is a key factor determining the nucleation path, and strong solvation could lead to LLPS. Additionally, the molecular self-assembly evolution during the crystallization process was further investigated by using small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS). The findings indicate that larger clusters with a diffuse transition layer may lead to LLPS during the nucleation process.

Intramolecular CH⋯π attraction mediated conformational polymorphism of constrained helical peptides

In nature, biochemical processes depend on polymorphism, a phenomenon by which discrete biomolecules can adopt specific conformations based on their environment. However, it is often difficult to explore the generation mechanism and achieve polymorphic control in artificial supramolecular assembly systems. In this work, we propose a feasible thought for exploring the transformation mechanism of polymorphism in peptide assembly from the perspective of thermodynamic regulation, which enables polymorphic composition to be limited by switchable intramolecular CH⋯π attraction within a certain temperature range. Combined with the density functional theory calculations, we obtained thermodynamic theoretical data supporting the conformation transition and the underlying polymorphism formation principle. Afterward, we properly designed the peptide to alter the probability of CH⋯π attraction occurring. Then, we selectively obtained a homogeneous morphological form with corresponding molecular conformation, which further demonstrated the important role of molecular conformational manipulation in polymorphism selection. This unique template-based strategy developed in this study may provide scientists with an additional line of thought to guide assembly paths in other polymorphic systems.

Regioselective super-assembly of Prussian blue analogue

The construction of high-asymmetrical structures demonstrates significant potential in improving the functionality and distinctness of nanomaterials, but remains a considerable challenge. Herein, we develop a one-pot method to fabricate regioselective super-assembly of Prussian blue analogue (PBA) -- a PBA anisotropic structure (PBA-AS) decorated with epitaxial modules--using a step-by-step epitaxial growth on a rapidly self-assembled cubic substrate guided by thiocyanuric acid (TCA) molecules. The epitaxial growth units manifest as diverse geometric shapes, which are predominantly concentrated on the {100}, {111}, or {100}+{111} crystal plane of the cubic substrate. The crystal plane and morphology of epitaxial module can be regulated by changing the TCA concentration and reaction temperature, enabling a high level of controllability over specific assembly sites and structures. To illustrate the advantage of the asymmetrical structure, phosphated PBA-AS demonstrates improved performance in the oxygen evolution reaction compared to simple phosphated PBA nanocube. This method offers valuable insights for designing asymmetrical nanomaterials with intricate architectures and versatile functionalities.

Direct Synthesis of CuPd Icosahedra Supercrystals Studied by In Situ X-Ray Scattering

Nanocrystal self-assembly into supercrystals provides a versatile platform for creating novel materials and devices with tailored properties. While common self-assembly strategies imply the use of purified nanoparticles after synthesis, conversion of chemical precursors directly into nanocrystals and then supercrystals in simple procedures has been rarely reported. Here, the nucleation and growth of CuPd icosahedra and their consecutive assembly into large closed-packed face-centered cubic (fcc) supercrystals are studied. To this end, the study simultaneously and in situ measures X-ray total scattering with pair distribution function analysis (TS-PDF) and small-angle X-ray scattering (SAXS). It is found that the supercrystals' formation is preceded by an intermediate dense phase of nanocrystals displaying short-range order (SRO). It is further shown that the organization of oleic acid/oleylamine surfactants into lamellar structures likely drives the emergence of the SRO phase and later of the supercrystals by reducing the volume accessible to particle diffusion. The supercrystals' formation as well as their disassembly are triggered by temperature. The study demonstrates that ordering of solvent molecules can be crucial in the direct synthesis of supercrystals. The study also provides a general approach to investigate novel preparation routes of supercrystals in situ and across several length scales via X-ray scattering.

β-CsHg2I5, a compound with rare [Hg2I5] dimers and large optical anisotropy

Hg-based compounds show abundant structural diversity and distinguished properties. Herein, a new phase transition compound CsHg2I5 was reported. The high-temperature phase β-CsHg2I5 with rare [Hg2I5] dimers was synthesized by the flux method at 573 K, and it shows a reversible phase transition at a low temperature of ∼100 K to form the low-temperature phase α-CsHg2I5. The two phases crystallize in the same P21/c space group, with different crystal structures. β-CsHg2I5 is composed of rare [Hg2I5] dimers and [CsI11] polyhedral units, while α-CsHg2I5 is composed of [Hg4I11] and [CsI10] units. The experimental band gap of β-CsHg2I5 was found to be 2.58 eV. Owing to the presence of [Hg2I5]∞ pseudo-layers, β-CsHg2I5 exhibits large optical anisotropy with a calculated birefringence of 0.132@1064 nm. Meanwhile, β-CsHg2I5 is a congruent compound and the congruent point is ∼481 K. Theoretical calculations indicate that the rare [Hg2I5] dimer is a nonlinear active unit, which can be used as a new fundamental building block for the design of advanced nonlinear optical materials. Moreover, a CsI-HgI2 pseudo-binary diagram was drawn. The results enrich the structural diversity of Hg-based halides and give some insights into the development of new functional materials based on rare [Hg2I5] dimers.

Prussian Blue Analogue Glasses for Photoinduced CO2 Conversion

Crystal-to-glass transformation is a powerful approach to modulating the chemical and physical properties of crystals. Here we demonstrate that the glass transformation of cobalt hexacyanoferrate crystals, one of the Prussian blue analogues, increased the concentration of open metal sites and altered the electronic state while maintaining coordination geometries and short-range ordering in the structure. The compositional and structural changes were characterized by X-ray absorption fine structure, energy dispersive X-ray spectroscopy, and X-ray total scattering. The changes contribute to the flat band potential of the glass becoming closer to the redox potential of CO2 reduction. The valence band energy of the glass also shifts, resulting in lower band gap energy. Both the increased open metal sites and the optimal electronic structure upon vitrification enhance photocatalytic activity toward CO2-to-CO conversions (9.9 μmol h-1 CO production) and selectivity (72.4%) in comparison with the crystalline counterpart (3.9 μmol h-1 and 42.8%).

Shearing-induced formation of Au nanowires

Shearing-induced nucleation is known in our daily lives, yet rarely discussed in nano-synthesis. Here, we demonstrate an unambiguous shearing-induced growth of Au nanowires. While in static solution Au would predominately deposit on pre-synthesized triangular nanoplates to form nano-bowls, the introduction of stirring or shaking gives rise to nanowires, where an initial nucleation could be inferred. Under specific growth conditions, CTAB is responsible for stabilizing the growth materials and the resulting oversaturation promotes shearing-induced nucleation. At the same time, all Au surfaces are passivated by ligands, so that the growth materials are diverted to relatively fresher sites. We propose that the different degrees of "focused growth" in active surface growth could be represented by watersheds of different slopes, so that the subtle differences between neighbouring sites would set course to opposite pathways, with some sites becoming ever more active and others ever more inhibited. The shearing-induced nuclei, with their initially ligand-deficient surface and higher accessibility to growth materials, win the dynamic inter-particle competition against other sites, explaining the dramatic diversion of growth materials from the seeds to the nanowires.

Tunable Optical Anisotropy in Rare-Earth Borates with Flexible [BO3] Clusters

Borates have garnered a lot of attention in the realm of solid-state chemistry due to their remarkable characteristics, in which the synthesis of borates with isolated [BO3] by adding rare-earth elements is one of the main areas of structural design study. Five new mixed-metal Y-based rare-earth borates, Ba2ZnY2(BO3)4, KNa2Y(BO3)2, Li2CsY4(BO3)5, LiRb2Y(BO3)2, and RbCaY(BO3)2, have been discovered using the high-temperature solution approach. Isolated [BO3] clusters arranged in various configurations comprise their entire anionic framework, allowing for optical anisotropy tuning between 0.024 and 0.081 under 1064 nm. In this study, we characterize the relative placements of their [BO3] groups and examine how their structure affects their characteristics. The origin of their considerable optical anisotropy has been proven theoretically. This study unequivocally demonstrates that even a slight alteration to borates' anionic structure can result in a significant improvement in performance.

Seeding Atomic Silver into Internal Lattice Sites of Transition Metal Oxide for Advanced Electrocatalysis

Transition metal oxides (TMOs) are widely studied for loading of various catalysts due to their low cost and high structure flexibility. However, the prevailing close-packed nature of most TMOs crystals has restricted the available loading sites to surface only, while their internal bulk lattice remains unactuated due to the inaccessible narrow space that blocks out most key reactants and/or particulate catalysts. Herein, using tunnel-structured MnO2, this study demonstrates how TMO's internal lattice space can be activated as extra loading sites for atomic Ag in addition to the conventional surface-only loading, via which a dual-form Ag catalyst within MnO2 skeleton is established. In this design, not only faceted Ag nanoparticles are confined onto MnO2 surface by coherent lattice-sharing, Ag atomic strings are also seeded deep into the sub-nanoscale MnO2 tunnel lattice, enriching the catalytically active sites. Tested for electrochemical CO2 reduction reaction (eCO2RR), such dual-form catalyst exhibits a high Faradaic efficiency (94%), yield (67.3 mol g-1 h-1) and durability (≈48 h) for CO production, exceeding commercial Ag nanoparticles and most Ag-based electrocatalysts. Theoretical calculations further reveal the concurrent effect of such dual-form catalyst featuring facet-dependent eCO2RR for Ag nanoparticles and lattice-confined eCO2RR for Ag atomic strings, inspiring the future design of catalyst-substrate configuration.

Interrogation of 3d Transition Bimetallic Nanocrystal Nucleation and Growth Using In Situ Electron Microscope and Synchrotron X-ray Techniques

Understanding the nucleation and growth mechanism of 3d transition bimetallic nanocrystals (NCs) is crucial to developing NCs with tailored nanostructures and properties. However, it remains a significant challenge due to the complexity of 3d bimetallic NCs formation and their sensitivity to oxygen. Here, by combining in situ electron microscopy and synchrotron X-ray techniques, we elucidate the nucleation and growth pathways of Fe-Ni NCs. Interestingly, the formation of Fe-Ni NCs emerges from the assimilation of Fe into Ni clusters together with the reduction of Fe-Ni oxides. Subsequently, these NCs undergo solid-state phase transitions, resulting in two distinct solid solutions, ultimately dominated by γ-Fe3Ni2. Furthermore, we deconvolve the interplays between local coordination and electronic state concerning the growth temperature. We directly visualize the oxidation-state distributions of Fe and Ni at the nanoscale and investigate their changes. This work may reshape and enhance the understanding of nucleation and growth in atomic crystallization.

Acceleration of radiative recombination for efficient perovskite LEDs

The increasing demands for more efficient and brighter thin-film light-emitting diodes (LEDs) in flat-panel display and solid-state lighting applications have promoted research into three-dimensional (3D) perovskites. These materials exhibit high charge mobilities and low quantum efficiency droop1-6, making them promising candidates for achieving efficient LEDs with enhanced brightness. To improve the efficiency of LEDs, it is crucial to minimize nonradiative recombination while promoting radiative recombination. Various passivation strategies have been used to reduce defect densities in 3D perovskite films, approaching levels close to those of single crystals3. However, the slow radiative (bimolecular) recombination has limited the photoluminescence quantum efficiencies (PLQEs) of 3D perovskites to less than 80% (refs. 1,3), resulting in external quantum efficiencies (EQEs) of LED devices of less than 25%. Here we present a dual-additive crystallization method that enables the formation of highly efficient 3D perovskites, achieving an exceptional PLQE of 96%. This approach promotes the formation of tetragonal FAPbI3 perovskite, known for its high exciton binding energy, which effectively accelerates the radiative recombination. As a result, we achieve perovskite LEDs with a record peak EQE of 32.0%, with the efficiency remaining greater than 30.0% even at a high current density of 100 mA cm-2. These findings provide valuable insights for advancing the development of high-efficiency and high-brightness perovskite LEDs.

Agglomeration inhibition engineering of nickel-cobalt alloys by a sacrificial template for efficient urea electrolysis

Designing efficient non-precious metal-based catalysts for urea oxidation reaction (UOR) is essential for achieving energy-saving hydrogen production and the treatment of wastewater containing ammonia. In this study, sodium dodecyl sulfate (SDS) is employed as a sacrificial template to synthesize NiCo alloy nanowires (NiCo(SDS)/CC), and the instinct formation mechanism is investigated. It is found that SDS can inhibit the Ostwald ripening during hydrothermal and calcination processes, which could release abundant active cobalt, thereby modulating the electronic structure to promote the catalytic reaction. Moreover, SDS as a sacrificial template can induce the deposition of metal atoms and increase the specific surface area of the catalyst, providing abundant active sites to accelerate the reaction kinetics. As expected, the NiCo(SDS)/CC exhibits good activity for both UOR and hydrogen evolution reactions (HER) and it requires only 1.31 V and -86 mV to obtain a current density of ±10 mA cm-2, respectively. This work provides a new strategy for reducing the agglomeration of transition metals to design high-performance composite catalysts for urea oxidation.

Platinum-Ruthenium Dual-Atomic Sites Dispersed in Nanoporous Ni0.85Se Enabling Ampere-Level Current Density Hydrogen Production

Alkaline anion-exchange-membrane water electrolyzers (AEMWEs) using earth-abundant catalysts is a promising approach for the generation of green H2. However, the AEMWEs with alkaline electrolytes suffer from poor performance at high current density compared to proton exchange membrane electrolyzers. Here, atomically dispersed Pt-Ru dual sites co-embedded in nanoporous nickel selenides (np/Pt1Ru1-Ni0.85Se) are developed by a rapid melt-quenching approach to achieve highly-efficient alkaline hydrogen evolution reaction. The np/Pt1Ru1-Ni0.85Se catalyst shows ampere-level current density with a low overpotential (46 mV at 10 mA cm-2 and 225 mV at 1000 mA cm-2), low Tafel slope (32.4 mV dec-1), and excellent long-term durability, significantly outperforming the benchmark Pt/C catalyst and other advanced large-current catalysts. The remarkable HER performance of nanoporous Pt1Ru1-Ni0.85Se is attributed to the strong intracrystal electronic metal-support interaction (IEMSI) between Pt-Se-Ru sites and Ni0.85Se support which can greatly enlarge the charge redistribution density, reduce the energy barrier of water dissociation, and optimize the potential determining step. Furthermore, the assembled alkaline AEMWE with an ultralow Pt and Ru loading realizes an industrial-level current density of 1 A cm-2 at 1.84 volts with high durability.

Polysulfide Anions [Sx]2- (x = 2, 3, 4, 5): Promising Functional Building Units for Infrared Nonlinear Optical Materials

Infrared nonlinear optical (IR NLO) materials play significant roles in laser technology. The novel functional building units (FBUs) are of great importance in constructing NLO materials with strong second harmonic generation (SHG). Herein, polysulfide anion [Sx]2- (x = 2, 3, 4, 5) units are investigated on NLO-related properties and structure-performance relationships. Theoretical calculations uncover that the [Sx]2- (x = 2, 3, 4, 5) units are potential IR NLO FBUs with large polarizability anisotropy (δ), hyperpolarizability (β) and wide HOMO-LUMO gap. Fourteen crystals including [Sx]2- (x = 2, 3, 4, 5) units are calculated and analyzed. The results show that these units can result in a wide IR transmittance range, significant SHG effects, wide band gap Eg (Na2S4: Eg = 3.09 eV), and large birefringence Δn [BaS3 (P21212): Δn = 0.70]. More importantly, it is highlighted that the crystal materials including with [Sx]2- (x = 2, 3, 4, 5) groups are good candidates for the exploration of the outstanding IR NLO materials.

Discovery of a new bimetallic borate with strong optical anisotropy activated by π-conjugated [B2O5] units

Birefringent materials with high optical anisotropy have been identified as a research hotspot owing to their significant scientific and technological significance in modern optoelectronics for manipulating light polarization. Researchers studying borate systems have discovered that adding π-conjugated units placed in parallel can significantly increase the birefringence of crystalline solids; some examples include [BO3] units, [B2O5] units, and [B3O6] units. However, there are not many borates with strictly parallel configurations of π-conjugated [B2O5] units. In this study, a new bimetallic borate Sr2Cd4(B2O5)3 with near-parallel arrangement of π-conjugated [B2O5] units was discovered. Sr2Cd4(B2O5)3 possesses the maximum number density of [B2O5] units, shortest dihedral angle of [B2O5] units (between the two [BO3]), and largest degree of [CdO6] octahedral distortion among all the currently known Sr-Cd-B-O tetragonal system borates, making it demonstrate a large birefringence of 0.102 at 532 nm. Theoretical analysis proves that π-conjugated [B2O5] anions are the primary source of the large birefringence of Sr2Cd4(B2O5)3.

Wide band gap selenide infrared nonlinear optical materials AIIMg6Ga6Se16 with strong SHG responses and high laser-induced damage thresholds

Infrared (IR) nonlinear optical (NLO) materials with strong NLO response, wide band gap and high laser-induced damage threshold (LIDT) are highly expected in current laser technologies. Herein, by introducing double alkaline-earth metal (AEM) atoms, three wide band gap selenide IR NLO materials AIIMg6Ga6Se16 (AII = Ca, Sr, Ba) with excellent linear and NLO optical properties have been rationally designed and fabricated. AIIMg6Ga6Se16 (AII = Ca, Sr, Ba) are composed of unique [AIISe6] triangular prisms, [MgSe6] octahedra and [GaSe4] tetrahedra. The introduction of double AEMs effectively broadens the band gaps of selenide-based IR NLO materials. Among them, CaMg6Ga6Se16, achieving the best balance between the second-harmonic generation response (∼1.5 × AgGaS2), wide band gap (2.71 eV), high LIDT (∼9 × AgGaS2), and moderate birefringence of 0.052 @ 1064 nm, is a promising NLO candidate for high power IR laser. Theoretical calculations indicate that the NLO responses and band gaps among the three compounds are mainly determined by the NLO-active [GaSe4] units. The results enrich the chemical diversity of chalcogenides, and give some insight into the design of new functional materials based on the rare [AIISe6] prismatic units.

Understanding the bio-crystallization: An insight to therapeutic relevance

In the realm of biomedical engineering and materials science, the synthesis of biomaterials plays a pivotal role in advancing therapeutic strategies for regeneration of tissues. The deliberate control of crystallization processes in biomaterial synthesis has emerged as a key avenue for tailoring the properties of these materials, enabling the design of innovative solutions for a wide array of medical applications. This review delves into the interplay between controlled crystallization and biomaterial synthesis, exploring its multifaceted applications in the therapeutic domains. The investigation encompasses a wide spectrum of matrices, ranging from small molecules to large biomolecules, highlighting their unique contributions in modulating crystallization processes. Furthermore, the review critically assesses the analytical techniques and methodologies employed to probe and characterize the depths of crystallization dynamics. Advanced imaging, spectroscopic, and computational tools are discussed in the context of unraveling the intricate mechanisms governing nucleation and crystallization processes within the organic matrix. Finally we delve in the applications of such advance material in therapeutics of hard and soft tissues.

Catalytic Activity and Electrochemical Stability of Ru1-xMxO2 (M = Zr, Nb, Ta): Computational and Experimental Study of the Oxygen Evolution Reaction

We use computations and experiments to determine the effect of substituting zirconium, niobium, and tantalum within rutile RuO2 on the structure, oxygen evolution reaction (OER) mechanism and activity, and electrochemical stability. Calculated electronic structures altered by Zr, Nb, and Ta show surface regions of electron density depletion and accumulation, along with anisotropic lattice parameter shifts dependent on the substitution site, substituent, and concentration. Consistent with theory, X-ray photoelectron spectroscopy experiments show shifts in binding energies of O-2s, O-2p, and Ru-4d peaks due to the substituents. Experimentally, the substituted materials showed the presence of two phases with a majority phase that contains the metal substituent within the rutile phase and a second, smaller-percentage RuO2 phase. Our experimental analysis of OER activity shows Zr, Nb, and Ta substituents at 12.5 atom % induce lower activity relative to RuO2, which agrees with computing the average of all sites; however, Zr and Ta substitution at specific sites yields higher theoretical OER activity than RuO2, with Zr substitution suggesting an alternative OER mechanism. Metal dissolution predictions show the involvement of cooperative interactions among multiple surface sites and the electrolyte. Zr substitution at specific sites increases activation barriers for Ru dissolution, however, with Zr surface dissolution rates comparable to those of Ru. Experimental OER stability analysis shows lower Ru dissolution from synthesized RuO2 and Zr-substituted RuO2 compared to commercial RuO2 and comparable amounts of Zr and Ru dissolved from Zr-substituted RuO2, aligned with our calculations.

AIB3 IIC2 IIIQ6 VIXVII: A Thioborate Halide Family for Developing Wide Bandgap Infrared Nonlinear Materials by Coupling Planar [BS3] and Polycations

Developing high-performance infrared (IR) nonlinear optical (NLO) materials is urgent but challenging due to the competition between NLO coefficient and bandgap in one compound. Herein, by coupling NLO-active [BS3] planar units and halide-centered polycations, six new metal thioborate halides ABa3B2S6X (A = Rb, Cs; X = Cl, Br, I) composed of zero-dimensional [XBamRbn/Csn] polycations and [BS3] units, belonging to a newA I B 3 II C 2 III Q 6 VI X VII ${\mathrm{A}}^{\mathrm{I}}{\mathrm{B}}_{3}^{\mathrm{II}}{\mathrm{C}}_{2}^{\mathrm{III}}{\mathrm{Q}}_{6}^{\mathrm{VI}}{\mathrm{X}}^{\mathrm{VII}}$ family, are rationally designed and fabricated. The compounds show an interesting structural transition from Pbcn (ABa3B2S6Cl) to Cmc21 (ABa3B2S6Br and ABa3B2S6I) driven by the clamping effect of polycationic frameworks. ABa3B2S6Br and ABa3B2S6I are the first series metal thioborate halide IR NLO materials, and the introduction of [BS3] unit effectively widens the bandgap of planar unit-constructed chalcogenides. ABa3B2S6Br and ABa3B2S6I, exhibiting wide bandgaps (3.55-3.60 eV), high laser-induced damage thresholds (≈ 6 × AgGaS2), and strong SHG effects (0.5-0.6 × AgGaS2) with phase-matching behaviors, are the promising IR NLO candidates for high-power laser applications. The results enrich the chemical and structural diversity of boron chemistry and give some insights into the design of new IR NLO materials with planar units.

Transient intermediate in the formation of an amorphous metal-organic framework

Amorphous metal-organic frameworks are rarely formed via direct synthesis. Our limited understanding of their atomic assembly in solution prevents full exploitation of their unique structural complexity. Here, we use in situ synchrotron X-ray absorption spectroscopy with sub-second time resolution to probe the formation of the amorphous Fe-BTC framework. Using a combination of spectral fingerprinting, linear combination analysis, and principal component analysis coupled with kinetic analyses, we reveal a multi-stage formation mechanism that, crucially, proceeds via the generation of a transient intermediate species.

Comparing brute force to transition path sampling for gas hydrate nucleation with a flat interface: comments on time reversal symmetry

Fluid to solid nucleation is often investigated with the rare event method transition path sampling (TPS). I claim that the inherent irreversibility of solid nucleation, even at stationary conditions, calls into question TPS's applicability for determining solid nucleation mechanisms, especially for pre-critical behavior. Even when applied to a phenomenon which displays time reversal asymmetry like solid nucleation, TPS is a good means of exploring phase space and giving trends in post-critical structure, and its ability to facilitate nucleation rate and free energy calculations remains outstanding. Forward-only splitting and ratcheting methods such as forward flux sampling are more attractive for understanding nucleation mechanisms as they do not require time reversal symmetry, but at low driving forces may suffer from the same limitations as brute force: they may never make it to the first ratchet. Here I briefly summarize the TPS method and gas hydrate nucleation simulation literature, focusing on topics within both to facilitate a comparison of brute force hydrate nucleation to transition path sampling of hydrate nucleation. Perhaps anecdotally, the brute force technique results in more crystalline trajectories despite having higher driving forces than TPS. I maintain this difference is because of the inherent irreversibility of hydrate nucleation, meaning its pre-critical behavior cannot accurately be determined by the melting trajectories that comprise approximately half of the configurations in TPS's path ensemble.

Design of Deep-Ultraviolet Zero-Order Waveplate Materials by Rational Assembly of [AlO2F4] and [SO4] Groups

Zero-order waveplates are widely used in the manufacture of laser polarizer waves, which are important in polarimetry and the laser industry. However, there are still challenges in designing deep-ultraviolet (DUV) waveplate materials that satisfy large band gaps and small optical anisotropy simultaneously. Herein, three cases of aluminum sulfate fluorides: Na2AlSO4F3, Li4NH4Al(SO4)2F4, and Li6K3Al(SO4)4F4, with novel [AlSO4F3] layers or isolated [AlS2O8F4] trimers were designed and synthesized by the rational assembly of [AlO2F4] and [SO4] groups through a hydrothermal method. Experiments and theoretical calculations imply that these three possess short cutoff edges (λ < 200 nm) and small birefringence (0.0014-0.0076 @ 1064 nm), which fulfils the prerequisite for potential DUV zero-order waveplate materials. This work extends the exploration of DUV zero-order waveplate materials to the aluminum sulfate fluoride systems.

Fluorination Strategy Towards Symmetry Breaking of Boron-centered Tetrahedron for Poly-fluorinated Optical Crystals

Borate crystals can be chemically and functionally modified by the fluorination strategy, which encourages the identification of emerging fluorooxoborates with a structure and set of characteristics not seen in any other oxide parents. However, the bulk of fluorooxoborates have been found accidentally, rational methods of synthesis are required, particularly for the infrequently occurring poly-fluorinated components. Herein, we reported the use of bifluoride salts as a potent source of fluorine to prepare fluorooxoborates that contain rarely tri-fluorinated [BF3 X] (X=O and CH3 ) tetrahedra and eleven compounds were found. We identified the optical properties of the organofluorinated group [CH3 BF3 ] and their potential for nonlinear optics for the first time. Among these, two non-centrosymmetric components hold potential for the production of 266 nm harmonic coherent light for nonlinear optics, and more crucially, have the benefit of growing large size single crystals. Our study establishes experimental conditions for the coexistence of the diverse functional groups, enabling the production of poly-fluorinated optical crystals.

Theoretical prediction on the stability, elastic, electronic and optical properties of MAB-phase M4AlB4 compounds (M = Cr, Mo, W)

This research employs first-principles calculations to address the challenges presented by processing complexity and low damage tolerance in transition metal borides. The study focuses on designing and investigating MAB phase compounds of M4AlB4 (M = Cr, Mo, W). We conduct a comprehensive assessment of the stability, phononic, electronic, elastic, and optical properties of Cr4AlB4, Mo4AlB4, and W4AlB4. The calculated results reveal formation enthalpies of -0.516, -0.490, and -0.336 eV per atom for Cr4AlB4, Mo4AlB4, and W4AlB4, respectively. Notably, W4AlB4 emerges as a promising precursor material for MABene synthesis, demonstrating exceptional thermal shock resistance. The dielectric constants ε1(0) were determined as 126.466, 80.277, and 136.267 for Cr4AlB4, Mo4AlB4, and W4AlB4, respectively. Significantly, W4AlB4 exhibits remarkably high reflectivity (>80%) within the wavelength range of 19.84-23.6 nm, making it an ideal candidate for extreme ultraviolet (EUV) reflective coatings. The insights gleaned from this study provide a strong research framework and theoretical guidance for advancing the synthesis of innovative MAB-phase compounds.

The Strain Effects and Interfacial Defects of Large ZnSe/ZnS Core/Shell Nanocrystals

The shell growth of large ZnSe/ZnS nanocrystals( is of great importance in the pursuit of pure-blue emitters for display applications, however, suffers from the challenges of spectral blue-shifts and reduced photoluminescence quantum yields. In this work, the ZnS shell growth on different-sized ZnSe cores is investigated. By controlling the reactivity of Zn and S precursors, the ZnS shell growth can be tuned from defect-related strain-released to defect-free strained mode, corresponding to the blue- and red-shifts of resultant nanocrystals respectively. The shape of strain-released ZnSe/ZnS nanocrystals can be kept nearly spherical during the shell growth, while the shape of strained nanocrystals evolutes from spherical into island-like after the critical thickness. Furthermore, the strain between ZnSe core and ZnS shell can convert the band alignment from type-I into type-II core/shell structure, resulting in red-shifts and improved quantum yield. By correlating the strain effects with interfacial defects, a strain-released shell growth model is proposed to obtain large ZnSe/ZnS nanocrystals with isotropic shell morphology.

Mineral scaling induced membrane wetting in membrane distillation for water treatment: Fundamental mechanism and mitigation strategies

The scaling-induced wetting phenomenon seriously affects the application of membrane distillation (MD) technology in hypersaline wastewater treatment. Unlike the large amount of researches on membrane scaling and membrane wetting, scaling-induced wetting is not sufficiently studied. In this work, the current research evolvement of scaling-induced wetting in MD was systematically summarized. Firstly, the theories involving scaling-induced wetting were discussed, including evaluation of scaling potential of specific solutions, classical and non-classical crystal nucleation and growth theories, observation and evolution of scaling-induced processes. Secondly, the primary pretreatment methods for alleviating scaling-induced wetting were discussed in detail, focusing on adding agents composed of coagulation, precipitation, oxidation, adsorption and scale inhibitors, filtration including granular filtration, membrane filtration and mesh filtration and application of external fields including sound, light, heat, electromagnetism, magnetism and aeration. Then, the roles of operation conditions and cleaning conditions in alleviating scaling-induced wetting were evaluated. The main operation parameters included temperature, flow rate, pressure, ultrasound, vibration and aeration, while different types of cleaning reagents, cleaning frequency and a series of assisted cleaning measures were summarized. Finally, the challenges and future needs in the application of nucleation theory to scaling-induced wetting, the speculation, monitoring and mitigation of scaling-induced wetting were proposed.

Observing the Evolution of Metal Oxides in Liquids

Metal oxides with diverse compositions and structures have garnered considerable interest from researchers in various reactions, which benefits from transmission electron microscopy (TEM) in determining their morphologies, phase, structural and chemical information. Recent breakthroughs have made liquid-phase TEM a promising imaging platform for tracking the dynamic structure, morphology, and composition evolution of metal oxides in solution under work conditions. Herein, this review introduces the recent advances in liquid cells, especially closed liquid cell chips. Subsequently, the recent progress including particle growth, phase transformation, self-assembly, core-shell nanostructure growth, and chemical etching are introduced. With the late technical advances in TEM and liquid cells, liquid-phase TEM is used to characterize many fundamental processes of metal oxides for CO2 reduction and water-splitting reactions. Finally, the outlook and challenges in this research field are discussed. It is believed this compilation inspires and stimulates more efforts in developing and utilizing in situ liquid-phase TEM for metal oxides at the atomic scale for different applications.

In situ observation of a stepwise [2 + 2] photocycloaddition process using fluorescence spectroscopy

Using highly sensitive and selective in situ techniques to investigate the dynamics of intermediates formation is key to better understand reaction mechanisms. However, investigating the early stages of solid-state reactions/transformations is still challenging. Here we introduce in situ fluorescence spectroscopy to observe the evolution of intermediates during a two-step [2 + 2] photocycloaddition process in a coordination polymer platform. The structural changes and kinetics of each step under ultraviolet light irradiation versus time are accompanied by the gradual increase-decrease of intensity and blue-shift of the fluorescence spectra from the crystals. Monitoring the fluorescence behavior using a laser scanning confocal microscope can directly visualize the inhomogeneity of the photocycloaddition reaction in a single crystal. Theoretical calculations allow us to rationalize the fluorescence behavior of these compounds. We provide a convenient strategy for visualizing the solid-state photocycloaddition dynamics using fluorescence spectroscopy and open an avenue for kinetic studies of a variety of fast reactions.

Parallel Nanosheet Arrays for Industrial Oxygen Production

According to the traditional nucleation theory, crystals in solution nucleate under thermal fluctuations with random crystal orientation. Thus, nanosheet arrays grown on a substrate always exhibit disordered arrangements, which impede mass transfer during catalysis. To overcome this limitation, here, we demonstrate stress-induced, oriented nucleation and growth of nanosheet arrays. A regularly self-growing parallel nanosheet array is realized on a curved growth substrate. During electrochemical oxygen production, the ordered array maintains a steady flow of liquids in the microchannels, suppressing the detrimental production of flow-blocking oxygen bubbles typical of randomly oriented nanosheet arrays. Controllable parallel arrays, fully covered fluffy-like ultrathin nanosheets, and amorphous disordered structures altogether enable full-scale design of hierarchical interfaces from the micro- to the atomic scale, significantly improving the otherwise sluggish kinetics of oxygen evolution toward industrial ultrafast production. Record-high ultrafast oxygen production of 135 L·min-1·m-2 with high working current of 4000 mA·cm-2 is steadily achieved at a competitively low cell voltage of 2.862 V. These results and related insights lay the basis for further developments in oriented nucleation and growth of crystals beyond classical nucleation approaches, with benefits for large-scale, industrial electrochemical processes as shown here for ultrafast oxygen production.

Kinetically Controlled Nucleation Enabled by Tunable Microfluidic Mixing for the Synthesis of Dendritic Au@Pt Core/Shell Nanomaterials

The nucleation stage plays a decisive role in determining nanocrystal morphology and properties; hence, the ability to regulate nucleation is critical for achieving high-level control. Herein, glass microfluidic chips with S-shaped mixing units are designed for the synthesis of Au@Pt core/shell materials. The use of hydrodynamics to tune the nucleation kinetics is explored by varying the number of mixing units. Dendritic Au@Pt core/shell nanomaterials are controllably synthesized and a formation mechanism is proposed. As-synthesized Au@Pt exhibited excellent ethanol oxidation activity under alkaline conditions (8.4 times that of commercial Pt/C). This approach is also successfully applied to the synthesize of Au@Pd core/shell nanomaterials, thus demonstrating its generality.

Synthesis, structure and characterization of Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers

A new mixed anionic compound Cd2TeO3Cl2 with unprecedented [Cd2O6Cl4] octahedral dimers has been synthesized, and millimeter-scale single crystals of Cd2TeO3Cl2 have been grown by the vertical Bridgman method with CdCl2 as the flux. Cd2TeO3Cl2 crystallizes in the centrosymmetric P1̄ (no. 2) space group, and shows a mixed cationic layer structure constituted by distorted [TeO3] motifs, mixed anionic [Cd2O6Cl4] chains, and [Cd2O6Cl4] octahedral dimers. Experimental and theoretical results show that Cd2TeO3Cl2 is a direct band gap compound with an experimental band gap of ∼4.25 eV. Meanwhile, the compound has good optical transmittance in the 3-5 μm atmospheric window. The results indicate that Cd2TeO3Cl2 could be used as a promising mid-IR window material, and could enrich the chemical and structural diversity of oxides.

Ba3(BS3)(PS4): the first alkaline-earth metal thioborate-thiophosphate with strong optical anisotropy originating from planar [BS3] units

The first alkaline-earth metal thioborate-thiophosphate Ba3(BS3)(PS4) was designed from Ba3(BO3)(PO4) by S-O substitution and fabricated experimentally. The [BS3] pseudo-layers formed in the structure contribute to the strong optical anisotropy and a large birefringence of ∼0.11 at 1064 nm. The results enrich the structural and chemical diversity of chalcogenides.

Breaking the Inherent Interarrangement of [B3O6] Clusters for Nonlinear Optics with Orbital Hybridization Enhancement

The [B3O6] group as a prime functional unit provides borates with intrinsic properties that are modified by coordination to cations. Inherent [B3O6] cluster structures in borates exclusively made of them have a near-plane configuration, with more than 90% of them having a maximum dihedral angle of zero and the remaining ones being less than 13°. Although such an inherent configuration can produce considerable birefringence for good phase-matching ability, this is not conducive to obtaining high conversion efficiency and beam quality due to the walk-off effects in the nonlinear optical process. In this article, two new borate halides Ca2B3O6X (X = Cl and Br) were reported, in which the confinement effects of distorted halogen-centered secondary building blocks compress the existence space of [B3O6] primitives, resulting in the nonparallel arrangement between [B3O6] clusters in this series. Both compounds show large second harmonic generation effects, and more importantly, the broken inherent interarrangement of [B3O6] clusters makes them a moderate birefringence and small walk-off angle. Their moderate birefringence is due to the large angular alignment between [B3O6] clusters, resulting from the orbital hybridization between the Ca s and the O p orbitals of the terminal O atoms on [B3O6] clusters. Our model supports this viewpoint and offers guidelines for rearranging [B3O6] clusters' arrangements in borates.

Zn2 HgP2 S8 : A Wide Bandgap Hg-Based Infrared Nonlinear Optical Material with Large Second-Harmonic Generation Response

Hg-based chalcogenides, as good candidates for the exploration of high-performance infrared (IR) nonlinear optical (NLO) materials, usually exhibit strong NLO effects, but narrow bandgaps. Herein, an unprecedented wide bandgap Hg-based IR NLO material Zn2 HgP2 S8 (ZHPS) with diamond-like structure is rationally designed and fabricated by a tetrahedron re-organization strategy with the aid of structure and property predictions. ZHPS exhibits a wide bandgap of 3.37 eV, which is the largest one among the reported Hg-based chalcogenide IR NLO materials and first breaks the 3.0 eV bandgap "wall" in this system, resulting in a high laser-induced damage threshold (LIDT) of ≈2.2 × AgGaS2 (AGS). Meanwhile, it shows a large NLO response (1.1 × AGS), achieving a good balance between bandgap (≥3.0 eV) and NLO effect (≥1 × AGS) for an excellent IR NLO material. DFT calculations uncover that, compared to normal [HgS4 ]n , highly distorted [HgS4 ]d tetrahedral units are conducive to generating wide bandgap, and the wide bandgap in ZHPS can be attributed to the strong s-p hybridization between Hg─S bonding in distorted [HgS4 ]d , which gives some insights into the design of Hg-based chalcogenides with excellent properties based on distorted [HgS4 ]d tetrahedra.

KRb2(NO3)2Cl: a new birefringent crystal exhibiting a perovskite-related framework and a short cutoff edge

The combination of π-conjugated groups [NO3] and Cl-centered polyhedra generates a new birefringent crystal with a perovskite-related framework, KRb2(NO3)2Cl, which is the first alkali metal nitrate chloride synthesized by a mild hydrothermal method. It crystallizes in the orthorhombic space group pbam (no. 55). In addition, KRb2(NO3)2Cl crystals with dimensions up to 7 × 1.5 × 1 mm3 were grown. Notably, KRb2(NO3)2Cl has a short UV cut-off edge (below 228 nm) and a significantly enhanced birefringence (Δn = 0.084 at 1064 nm). Theoretical calculations indicate that the birefringence enhancement mainly derives from π-conjugated [NO3] plane triangles.

Hydroxyfluorooxoborate (NH4)[C(NH2)3][B3O3F4(OH)] for exploring the effects of cation substitution on structure and optical properties

Cation substitution is a straightforward but effective technique for improving the structure and properties; however, controlling directed substitution still poses significant difficulties. Herein, a metal-free hydroxyfluorooxoborate (NH4)[C(NH2)3][B3O3F4(OH)] has been synthesized using the strategy of heterologous substitution based on the template of A2[B3O3F4(OH)]. Tunable structure and optical properties have been achieved via varied A-site cation substitution. The intrinsic mechanism for this tunability was established by crystallography and theoretical research.

Heterologous Isomorphic Substitution Induces Optical Property Enhancement for Deep-UV Crystals: a Case in Rb[B3O3F2(OH)2]

Optical anisotropy is pivotal for optical crystals, and it can be characterized by the maximum algebraic difference in refractive indices. Improving the optical anisotropy, especially for deep-ultraviolet (UV) crystals, is still a challenge and of interest. Herein, a new hydroxyfluorooxoborate, Rb[B3O3F2(OH)2], was obtained by the heterologous isomorphic substitution strategy. Dual enhancement for the band gap and birefringence compared with the parent A[B3O3F2(OH)2] (A = [Ph4P]/[Ph3MeP]) compounds was achieved in Rb[B3O3F2(OH)2]. This considerable enhancement originates from the removal of organic components and the retention of a birefringence-active anionic framework. This enhancement pushes the application region from UV to deep-UV. This discovery not only expands the structural chemistry of borates but also demonstrates the viability of heterologous isomorphic substitution to design deep-UV crystals with enhanced optical property.

MB3P2S10 (M = Rb, Cs): two new alkali metal thioboratephosphates with [B6P4S20] T3-supertetrahedra

Two new alkaline metal thioboratephosphates, RbB3P2S10 and CsB3P2S10, have been designed and fabricated by the flux method. The two compounds are composed of alkali metal polyhedral and [B6P4S20] T3-supertetrahedral units, and crystallize in I41/a and R3̄c space groups, respectively. The results enrich the chemical diversity of chalcogenides, and give insights for the exploration of new functional materials in thioboratephosphates.

Crystallization inhibitory effects of konjac glucomannan, sodium alginate and xanthan gum on curcumin in supersaturated solution

Supersaturating drug delivery system (SDDS) is a promising approach to enhance the solubility of hydrophobic functional components. However, SDDS is thermodynamically unstable and crystallization tends to occur. In this work, curcumin was used as a model compound, and the crystallization inhibitory effect of konjac glucomannan (KGM), sodium alginate (SA) and xanthan gum (XTG) on curcumin in supersaturated solution was investigated. Amorphous solubility of curcumin was determined using ultraviolet extinction, fluorescence spectroscopy and dynamic light scattering methods. Nucleation induction time (NIT) and crystal growth rate of curcumin were evaluated using ultraviolet probe in the absence and presence of various natural polysaccharides (NPs). Results showed that amorphous solubility of curcumin was approximately 30 μg/mL in pH 6.8 phosphate buffer. NPs used in this work restrained nucleation or crystal growth of curcumin effectively. The NITs of curcumin in the absence of NPs and in the presence of XTG, KGM and SA (1 μg/mL) were 3.7, 60.7, 20.0 and 8.0 min, respectively. The crystal growth rate of curcumin in the absence of NPs and in the presence of XTG, SA and KGM (1 μg/mL) were 0.0103, 0.00752, 0.00286 and 0.000306 min^-1, respectively. The nucleation inhibitory effect of NPs on curcumin was ranked as XTG > KGM > SA. The order of crystal growth inhibition capacity of NPs was KGM > SA > XTG. In conclusion, NPs could be incorporated into SDDS to maintain supersaturation of hydrophobic components for enhanced bioavailability.

BaMo3O10 Polymorphs with Tunable Symmetries and Properties

Polymorphism is a well-known but important phenomenon in the field of solid-state chemistry. Crystalline materials can form various polymorphs and present drastically varied physical and chemical properties. Herein, systematic exploration of the BaO-MoO₃ binary system leads to the discovery of a new barium molybdate, α-BaMo₃O₁₀. The temperature-dependent phase transition from α-BaMo₃O₁₀ to β-BaMo₃O₁₀ is confirmed. The tunable linear and nonlinear optical properties induced by the phase transition are confirmed by both experimental and theoretical approaches. Also, β-BaMo₃O₁₀ is identified as a nonlinear-optical crystal for the first time. The origin of linear- and nonlinear-optical properties of BaMo₃O₁₀ polymorphs is confirmed by the additional theoretical means. This work indicates that a small change in the structure can induce tunable symmetries and thereby widely divergent optical properties.

Design Rules for Obtaining Narrow Luminescence from Semiconductors Made in Solution

Solution-processed semiconductors are in demand for present and next-generation optoelectronic technologies ranging from displays to quantum light sources because of their scalability and ease of integration into devices with diverse form factors. One of the central requirements for semiconductors used in these applications is a narrow photoluminescence (PL) line width. Narrow emission line widths are needed to ensure both color and single-photon purity, raising the question of what design rules are needed to obtain narrow emission from semiconductors made in solution. In this review, we first examine the requirements for colloidal emitters for a variety of applications including light-emitting diodes, photodetectors, lasers, and quantum information science. Next, we will delve into the sources of spectral broadening, including "homogeneous" broadening from dynamical broadening mechanisms in single-particle spectra, heterogeneous broadening from static structural differences in ensemble spectra, and spectral diffusion. Then, we compare the current state of the art in terms of emission line width for a variety of colloidal materials including II-VI quantum dots (QDs) and nanoplatelets, III-V QDs, alloyed QDs, metal-halide perovskites including nanocrystals and 2D structures, doped nanocrystals, and, finally, as a point of comparison, organic molecules. We end with some conclusions and connections, including an outline of promising paths forward.

In situ TEM investigation of nucleation and crystallization of hybrid bismuth nanodiamonds

Despite great progress in the non-classical homogeneous nucleation and crystallization theory, the heterogeneous processes of atomic nucleation and crystallization remain poorly understood. Abundant theories and experiments have demonstrated the detailed dynamics of homogeneous nucleation; however, intensive dynamic investigations on heterogeneous nucleation are still rare. In this work, in situ transmission electron microscopy (TEM) at the atomic scale was carried out with temporal resolution for heterogeneous nucleation and crystallization. The results show a reversible amorphous to crystal phase transformation that is manipulated by the size threshold effect. Moreover, the two growth pathways of Bi particles can be mainly assigned to the atomic adsorption expansion in the amorphous state and effective fusion in the crystal contact process. These interesting findings, based on a real dynamic imaging system, strongly enrich and improve our understanding of the dynamic mechanisms in the non-classical heterogeneous nucleation and crystallization theory, providing insights into designing innovative materials with controlled microstructures and desired physicochemical properties.