Larger Atomic Radius Research Articles

Synergistic effect induces self crystallization of CsPbBr3 quantum dots in Borosilicate glass matrix By LiF

Cesium lead halide perovskite (CsPbX3) quantum dots (QDs) are recognized as viable substitutes for conventional fluorescent powder color converters, which can improve the color gamut and reproducibility of liquid crystal displays (LCDs). Encapsulating QDs in glass can effectively solve the water oxygen stability of QDs, but the glass matrix impedes the nucleation of QDs and the precipitation of QDs requires secondary heating. In our research, we successfully accomplished the self-crystallization of CsPbBr3 QDs facilitated by LiF within a B2O3-SiO2-ZnO borosilicate glass matrix.The results indicate that the self crystallization of CsPbBr3 QDs induced by LiF in borosilicate glass matrix has a synergistic effect. The Li+ ions can break the glass network structure and facilitate ionic migration and transport, while F- ions have good electronegativity due to ion aggregation, and can strongly attract Cs+ and Pb2+ ions with larger atomic radii, thereby promoting the rapid nucleation and growth of CsPbBr3 QDs, ultimately synthesizing QDs with uniform particle size, narrow half peak width, good optical properties, and thermal stability.

Surface Charge Regulation of Graphene by Fluorine and Chlorine Co-Doping for Constructing Ultra-Stable and Large Energy Density Micro-Supercapacitors.

Settling the structure stacking of graphene (G) nanosheets to maintain the high dispersity has been an intense issue to facilitate their practical application in the microelectronics-related devices. Herein, the co-doping of the highest electronegative fluorine (F) and large atomic radius chlorine (Cl) into G via a one-step electrochemical exfoliation protocol isengineered to actualize the ultralong cycling stability for flexible micro-supercapacitors (MSCs). Density functional theoretical calculations unveiled that the F into G can form the "ionic" C─F bond to increase the repulsive force between nanosheets, and the introduction of Cl can enlarge the layer spacing of G as well as increase active sites by accumulating the charge on pore defects. The co-doping of F and Cl generates the strong synergy to achieve high reversible capacitance and sturdy structure stability for G. The as-constructed aqueous gel-based MSC exhibited the superb cycling stability for 500,000 cycles with no capacitance loss and structure stacking. Furthermore, the ionic liquid gel-based MSC demonstrated a high energy density of 113.9mWhcm-3 under high voltage of up to 3.5V. The current work enlightens deep insights into the design and scalable preparation of high-performance co-doped G electrode candidate in the field of flexible microelectronics.

Effect of Alloying on the Hydrogen Sorption in Ti–Zr–Mn-Based Alloys. Pt. 1: C14-Type Laves-Phase-Based Alloys

The alloys of the Ti–Zr–Mn system based on the C14-type Laves phase are considered as ones of the most promising materials for safe storage and transportation of hydrogen. These alloys have appropriate parameters for activating the processes of absorption and release of hydrogen, a low cost, and a fairly high cyclic stability. In this work, the microstructure and phase composition of the starting alloys and the crystal structure of the hydrides synthesized from them are studied. Possible ways to reduce the cost of the final products are shown. The fact that changing the method of the alloy fabrication does not significantly affect its hydrogen absorption properties is shown. On the example of the considered alloys, it is shown that, as expected, alloying with an element with a larger atomic radius that forms a stable chemical compound with hydrogen results in an increase in the hydrogen capacity. This is explained by both the increased radius of the tetrahedral interstitial sites, where hydrogen atoms are located after dissolution, and the higher total amount of the element interacting with hydrogen.

Partially recrystallized heterostructure via Mo-doping endows CoCrNi medium-entropy alloy with exceptional strength and ductility

CoCrNi medium-entropy alloy (MEA) has excellent ductility, but the low strength at room temperature limits its practical usage. This study proposes an effective strategy to enhance the strength of CoCrNi MEA without apparent loss of ductility via partially recrystallized heterostructures resulted from doping of large atomic radius element, which was substantiated in a Mo-doping (CoCrNi)98Mo2 MEA. Compared with CoCrNi, the strength of (CoCrNi)98Mo2 is remarkably improved, maintaining the high uniform elongation of ∼24%. The yield strength and ultimate tensile strength increased from 950 MPa, 1287 MPa to 1131 MPa, 1564 MPa, respectively. The difference in deformation between the soft recrystallized region (SRR) and the hard non-recrystallized region (HNRR) leads to an excellent hetero-deformation induced (HDI) strengthening. Additionally, it is easier to reach the critical stress of twinning caused by high HDI stress at the interface of SRR/HNRR, which contributes to activation of high-density twins and produce dynamic Hall-Petch strengthening effect.

First-principles study of stability, order and disorder based on an entropy descriptor in noble and ferromagnetic transition metal alloys

Binary alloys AB composed of ferromagnetic metals A (Fe, Co, Ni) and the late 4d−5d noble metals B (Rh, Pd, Ag, Ir, Pt, Au) have been investigated using density functional theory with the generalized gradient approximation to understand the role of magnetism in the stability and the order–disorder transition which has an impact on their physicochemical properties, their applications and their possible implementation as precursors of high-entropy alloys. The enthalpy of formation related to the stability demonstrates that all the alloys are more stable in the ferromagnetic phase than in the nonmagnetic phase. The transition from ordered to disordered phases is quantified using a descriptor which is the standard deviation of the energy spectrum of a set of small nanoalloys with random atomic configurations. The study highlights the fact that the entropy-related descriptor, which is a quantity in determining the formation of a disordered phase as a solid solution or an ordered phase is highly dependent on the atomic environment. Despite the fact that the overall variation of this descriptor is supposed to be unpredictable, there is a noticeable trend showing that the environment-dependent ferromagnetism contributes to a chemical order in alloys and nanoalloys and that this order depends on the atomic radius of the species considered. The results indicate that species with small atomic radii, such as nickel, rhodium or iridium are more likely to form solid solutions than species with larger atomic radii and with more delocalized orbitals.

Stimulating Electron Delocalization of Lanthanide Elements through High-Entropy Confinement to Promote Electrocatalytic Water Splitting.

High-entropy alloys (HEAs) have aroused extensive attention in the field of catalysis. However, due to the integration of multiple active sites in HEA, it exhibits excessive adsorption behavior resulting in difficult desorption of active species from the catalyst surfaces, which hinders the catalytic efficiency. Therefore, adjusting the adsorption strength of the active site in HEA to enhance the catalytic activity is of great importance. By introducing rare-earth (RE) elements into the high-entropy alloy, the delocalization of 4f electrons can be achieved through the interaction between the multimetal active site and RE, which benefits to regulate the adsorption strength of the HEA surface. Herein, the RE Ce-modified hexagonal-close-packed PtRuFeCoNiZn-Ce/C HEAs are synthesized and showed an excellent electrocatalytic activity for hydrogen evolution reaction and oxygen evolution reaction with ultralow overpotentials of 4, 7 and 156, 132 mV, respectively, to reach 10 mA cm-2 in 0.5 M H2SO4 and 1.0 M KOH solutions, and the assembled water electrolysis cell only requires a voltage of 1.43 V to reach 10 mA cm-2, which is much better than the performance of PtRuFeCoNiZn/C. Combined with the results of in situ attenuated total reflection infrared spectroscopy and density functional theory (DFT), the fundamental reasons for the improvement of catalyst activity come from two aspects: (i) local lattice distortion of HEA caused by the introduction of RE with large atomic radius induces 4f orbital electron delocalization of RE elements and enhances electron exchange between RE and active sites. (ii) The electronegativity difference between the RE element and the active site forms a surface dipole in HEA, which optimizes the adsorption of the active intermediate by the HEA surface site. This study provides an insightful idea for the rational design of high-performance HEA- and RE-based electrocatalysts.

Revealing La doping activation or inhibition of crystal facet effects in Co3O4 for catalytic combustion and water resistance improvement

It was challenging to enhance the catalytic activity and water resistance of transition metal oxides in the CH4 treatment process. Here, La with large atomic radii was doped onto Co3O4 on the (110), (111) and (100) crystal facets, respectively, and successfully doped into the (110) and (100) lattices, but accumulation occurs on the (111) crystal surface. Doping La into the Co3O4 lattice achieved a dual excitation effect for surface optimization and structural defects, causing lattice expansion, enhancing the electrophilicity of the O atoms in the vicinity of La, and significantly stimulating the Co-O bond. This significantly improved reactive oxygen species content, CH4 adsorption capacity, and gaseous oxygen activation and replenishment capability for higher catalytic activity. Conversely, the (111) facet with accumulated La showed an opposite trend. Meanwhile, La doping effectively improved the stability of Co3O4 and weakened its hydrophilicity, which effectively enhanced its water resistance. This research provided a viable strategy for designing high-performance and water-resistant Co3O4-based catalysts.

Lattice distortion dependent physical and mechanical properties of VCoNi multi-principal element alloys

Multi-principal element alloys (MPEAs) have garnered widespread recognition owing to their remarkable mechanical properties. Among alloying elements, the vanadium (V) element exhibits unique characteristics and has a high strengthening effect in the face-centered cubic Co-Ni-V MPEAs family owing to its large atomic radius. Here, first-principle calculations are utilized to examine the physical and mechanical characteristics of extensively researched VCoNi MPEAs. The objectives of this work are to give guidance on the design of MPEAs with desirable capabilities and fresh insight for understanding the role of lattice distortion described by atomic size difference on lattice parameters, binding energy, generalized stacking-fault energy, elastic properties, and electronic properties. A high degree of lattice distortion can lead to an increase in lattice constants, a more stable structure, and enhanced plasticity. These trends are attributed to a shortened pseudo-energy gap, large variations in charge density difference, and compact band overlap with increasing lattice distortion. The above results aim to serve as a point of reference for exploring the physical and mechanical attributes of MPEAs.

Exploring the Use of "Honorary Transition Metals" To Push the Boundaries of Planar Hypercoordinate Alkaline-Earth Metals.

The quest for planar hypercoordinate atoms (phA) beyond six has predominantly focused on transition metals, with dodecacoordination being the highest reported thus far. Extending this bonding scenario to main-group elements, which typically lack d orbitals despite their larger atomic radius, has posed significant challenges. Intrigued by the potentiality of covalent bonding formation using the d orbitals of the heavier alkaline-earth metals (Ae = Ca, Sr, Ba), the so-called "honorary transition metals", we aim to push the boundaries of planar hypercoordination. By including rings formed by 12-15 atoms of boron-carbon and Ae centers, we propose a design scheme of 180 candidates with a phA. Further systematic screening, structural examination, and stability assessments identified 10 potential clusters with a planar hypercoordinate alkaline-earth metal (phAe) as the lowest-energy form. These unconventional structures embody planar dodeca-, trideca-, tetradeca-, and pentadecacoordinate atoms. Chemical bonding analyses reveal the important role of Ae d orbitals in facilitating covalent interactions between the central Ae atom and the surrounding boron-carbon rings, thereby establishing a new record for coordination numbers in the two-dimensional realm.

Rare-Earth Lanthanum-Evoked Amorphization and Optimization to Boost Ambient Nitrogen Fixation over Single-Atom Catalysts.

Single-atom catalysts (SACs) have been widely studied in a variety of electrocatalysis. However, its application in the electrocatalytic nitrogen reduction reaction (NRR) field still suffers from unsatisfactory performance, due to the sluggish mass transfer and significant kinetic barriers. Herein, a novel rare-earth-lanthanum-evoked optimization strategy is proposed to boost ambient NRR over SACs. The incorporation of La with a large atomic radius tends to break the atomic long-range order and trigger the amorphization of SACs, endowing a greater density of dangling bonds that could modify affinity for reactants and adsorbates. Moreover, with unique 5d16s2 valence-electron configurations, its presence could further enrich the electron density and enhance the intrinsic activity of single-metal center via the valence orbital coupling. As expected, the La-modified catalyst presents excellent activity toward the electrochemical NRR, delivering a maximum ammonia yield rate of 33.91 μg h-1 mg-1 and a remarkable Faradaic efficiency of 53.82%.

Temperature Effect on GaN Threshold Displacement Energy Under Low‐Energy Electron Beam Irradiation

AbstractUsing ab initio molecular dynamics (AIMD), the cascade collision process in GaN irradiated by low‐energy electron beam and the temperature effect on the threshold displacement energy (TDE) are investigated. The temperature effect of the TDE is found to exhibit different patterns for Ga and N primary knock‐on atoms (PKAs). In the considered energy range of initial kinetic energy (40 to 80 eV), displacements induced by Ga PKA show high uncertainty, i.e., the TDE energy strongly depends on the initial configurations, and kinetic energies higher than TDE does not ensure the displacements that form defects. On the contrary, temperature shows relatively small effect on its TDE and displacement induced by N PKAs, which can essentially occur when the PKA kinetic energy is higher than the TDE. Such different effects are possibly due to the different atomic radii of the two elements and the different energy barriers to overcome. Ga PKAs, which have larger atomic radii, are relatively difficult to stabilize in the crystal and tend to relax to its original position with the assistance of thermal vibrations, and vice versa for N PKAs. The simulation results provide a new understanding of TDE and the cascade collisions of PKAs in GaN at finite temperatures, which can be instructive for improving the radiation resistance of GaN devices.

Function mechanism of Fe in improving cycle stability and plateau characteristics of AB5-type hydrogen storage alloys

Rare-earth AB5-type alloys have great application potential in solid-state hydrogen storage. To further improve their plateau characteristics and cycling life, the effects of Fe on the long-term hydrogen storage properties of LaNi5-xFex (x = 0, 0.5, 1) alloys are studied, and the function mechanisms are revealed. Fe induces a (Fe,Ni) phase layer with good ductility around LaNi5 main phase, which plays a buffer role to relieve the microstrain during hydrogen absorption/desorption, thus stabilizing the crystal structure and improving the cycling performance. Further, Fe with larger atomic radius than Ni relieves the compression from 12o to 6 m site of the LaNi5 phase, and suppresses the plateau splitting phenomenon, resulting in a single and long hydrogen absorption/desorption plateau throughout 1000 cycles. This study promotes the understanding and application of cheap and effective Fe in improving the hydrogen storage properties of AB5-type alloys during long-term cycling.

Exploring NiCrAlYSiTa multicomponent coatings: Combining high-throughput synthesis and CALPHAD modeling

Multicomponent alloys pose great challenges for efficiently screening desired composition. Here, we combined high-throughput magnetron-sputtering experiments and CALculation of PHAse Diagrams (CALPHAD) methods to screen NiCrAlYSiTa coatings. The compositionally graded coatings showed increased amorphization with higher Si content, indicated by the steepen T0 curves and enlarged amorphous formation region. For the crystallized coatings, the phase structure transformed from Al- and Cr-rich bcc region to Ni-rich fcc, consistent with our calculated phase diagrams. Owing to the high cohesion energy and strong atomic bonding induced by large atomic radius difference and negative mixing enthalpy, the amorphous coatings exhibited superior hardness (25.8 GPa) and elastic modulus (415.8 GPa) compared to the reported multicomponent coatings. By combining high-throughput experimental and theoretical methods, this work pioneers an integrated framework for rapid development of new multicomponent alloy coatings.

Heavily phosphorus doped germanium with local strain compensation effect by Co-implantation and rapid thermal process

This study explored the effects and mechanisms of phosphorus (P), tin (Sn), and yttrium (Y) co-implantation in germanium (Ge). A series of dopant concentration measurements and electrical evaluations showed that the co-implantation process significantly enhanced P concentration in Ge, resulting in heavily doped regions. While P/Sn co-implantation showed limited advantages under low-temperature rapid thermal process (RTP), and P/Y co-implantation proved the effect of local strain compensation, the combined P/Sn/Y co-implantation achieved the highest concentration of P in Ge. At a RTP at 700 °C, we attained the remarkably high peak P concentration of 4.14×1020 atoms/cm3. This represents a 40-fold increase in P concentration compared to the conventional P single implantation method, using complementary metal-oxide semiconductor (CMOS)-compatible processes, and resulted in enhanced contact behavior. Geometric phase analysis (GPA) allowed visualization of the applied strains and stresses among the dopants and Ge atoms at nanometer resolution. The formation of strain-stress clusters by the large atomic radius Y was analyzed using GPA, and found to impact dopant distribution.

Recent Progress of Transition Metal Selenides for Electrochemical Oxygen Reduction to Hydrogen Peroxide: From Catalyst Design to Electrolyzers Application.

Hydrogen peroxide (H2O2) is a highly value-added and environmental-friendly chemical with various applications. The production of H2O2 by electrocatalytic 2e- oxygen reduction reaction (ORR) has emerged as a promising alternative to the energy-intensive anthraquinone process. High selectivity Catalysts combining with superior activity are critical for the efficient electrosynthesis of H2O2. Earth-abundant transition metal selenides (TMSs) being discovered as a classic of stable, low-cost, highly active and selective catalysts for electrochemical 2e- ORR. These features come from the relatively large atomic radius of selenium element, the metal-like properties and the abundant reserves. Moreover, compared with the advanced noble metal or single-atom catalysts, the kinetic current density of TMSs for H2O2 generation is higher in acidic solution, which enable them to become suitable catalyst candidates. Herein, the recent progress of TMSs for ORR to H2O2 is systematically reviewed. The effects of TMSs electrocatalysts on the activity, selectivity and stability of ORR to H2O2 are summarized. It is intended to provide an insight from catalyst design and corresponding reaction mechanisms to the device setup, and to discuss the relationship between structure and activity.

Dithiine-linked metalphthalocyanine framework with undulated layers for highly efficient and stable H2O2 electroproduction

Realization of stable and industrial-level H2O2 electroproduction still faces great challenge due large partly to the easy decomposition of H2O2. Herein, a two-dimensional dithiine-linked phthalocyaninato cobalt (CoPc)-based covalent organic framework (COF), CoPc-S-COF, was afforded from the reaction of hexadecafluorophthalocyaninato cobalt (II) with 1,2,4,5-benzenetetrathiol. Introduction of the sulfur atoms with large atomic radius and two lone-pairs of electrons in the C-S-C linking unit leads to an undulated layered structure and an increased electron density of the Co center for CoPc-S-COF according to a series of experiments in combination with theoretical calculations. The former structural effect allows the exposition of more Co sites to enhance the COF catalytic performance, while the latter electronic effect activates the 2e− oxygen reduction reaction (2e− ORR) but deactivates the H2O2 decomposition capability of the same Co center, as a total result enabling CoPc-S-COF to display good electrocatalytic H2O2 production performance with a remarkable H2O2 selectivity of >95% and a stable H2O2 production with a concentration of 0.48 wt% under a high current density of 125 mA cm−2 at an applied potential of ca. 0.67 V versus RHE for 20 h in a flow cell, representing the thus far reported best H2O2 synthesis COFs electrocatalysts.

Defect‐Passivating and Stable Benzothiophene‐Based Self‐Assembled Monolayer for High‐Performance Inverted Perovskite Solar Cells

AbstractEffective passivation of defects at the buried interface between the perovskite absorber and hole‐selective layer (HSL) is crucial for achieving high performance in inverted perovskite solar cells (PSCs). Additionally, the HSL needs to possess compact molecular packing and intrinsic photo‐ and thermo‐stability to ensure long‐term operation of the devices. In this study, a novel MeO‐BTBT‐based self‐assembled monolayer (SAM) is reported to serve as an efficient HSL in inverted PSCs. Compared to the well‐established carbazole‐containing SAM MeO‐2PACz, MeO‐BTBT has flat and more extended conjugation with large atomic radius of the sulfur atom. These induce stronger intermolecular interactions to enable more ordered and compact SAM to be formed on indium–tin oxide (ITO) substrates. Meanwhile, the sulfur atoms in MeO‐BTBT can coordinate with Pb2+ ions to passivate the defects at the buried interface of perovskite absorber. The derived perovskite films show both high photoluminescence (PL) quantum yield (13.2%) and a long lifetime (7.2 µs). The PSCs based on MeO‐BTBT show a PCE of 24.53% with an impressive fill factor of 85.3%. The PCEs of MeO‐BTBT‐based devices can maintain ≈95% of their initial values after being aged at 65 °C for more than 1000 h or continuous operation under 1‐sun illumination.

Atomic Scale Insight into the Oxidation Mechanism of Nb/Ta‐Doped Ti3SiC2/Al2O3 Ceramics

The low oxidation resistance of Ti3SiC2/Al2O3 composites limits their applications as high‐temperature structural materials. To improve the oxidation resistance, Nb and Ta are introduced into the substrate herein. The Nb/Ta‐doped Ti3SiC2/Al2O3 composite shows superior oxidation resistance than clean Ti3SiC2/Al2O3 following the oxidation process at 800–1000 °C for 100 h. The oxidation mechanism is determined via first‐principles calculations. The oxidation process of the composite is controlled by the inward diffusion of O and outward diffusion of Ti. When Nb/Ta elements are doped, their larger atomic radii and stronger binding produce a higher diffusion barrier for O and Ti atoms, which prevents element migration and reduces the thickness of the oxidation layers.

The Guidelines for the Design and Synthesis of Transition Metal Atom Doped Carbon Dots.

Atoms doping is a practical approach to modulate the physicochemical properties of carbon dots (CDs) and thus has garnered increasing attention in recent years. Compared to non-metal atoms, transition metal atoms (TMAs) possess more unoccupied orbitals and larger atomic radii. TMAs doping can significantly alter the electronic structure of CDs and bestow them with new intrinsic characteristics. TMAs-doped CDs have exhibited widespread application potential as a new class of single-atom-based nanomaterials. However, challenges remain for the successful preparation and precise design of TMAs-doped CDs. The key to successfully preparing TMA-doped CDs lies in anchoring TMAs to the carbon precursors before the reaction. Herein, taking the formation mechanism of TMAs-doped CDs as a starting point, we systematically summarized the ligands employed for synthesizing TMAs-doped CDs and proposed the synthetic strategy involving multiple ligands. Additionally, we summarize the functional properties imparted to CDs by different TMA dopants to guide the design of TMA-doped CDs with different functional characteristics. Finally, we describe the bottlenecks TMAs-doped CDs face and provide an outlook on their future development.

Nickel content-dependent microstructure and mechanical properties of TiZrNbHfNi high entropy alloy thin films

Alloying is known as an effective strategy to improve the mechanical properties of metallic materials. Here we show that the microstructure and mechanical behavior of a TiZrNbHf1.6 high entropy alloy film can be highly tuned by Ni addition. The newly designed TiZrNbHf1.6Nix (x = 0, 0.4, 1.2, 1.8, 2.5, 3.0, 4.6) alloy films are synthesized by co-sputtering Ti, Zr, Nb, Hf and Ni elemental targets. The microstructure and mechanical behavior of the alloy films are investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and nano/micro-indentations. The microstructural analysis indicates that the TiZrNbHf1.6 film has a single body-centered cubic with columnar-nanograined structure. As Ni content increases to 0.4 or above, the films show a complete amorphous structure. Our theoretical analysis shows that the transition from the crystalline to the amorphous structure can be attributed to the large atomic radius difference and the change of the thermodynamic parameters (e.g., mixing entropy and mixing enthalpy) due to the Ni addition. Compared to the TiZrNbHf1.6 film with a hardness of 4.8 GPa, a hardness increase of 8–35% is achieved in the Ni-doped alloy films (5.2–6.5 GPa) as measured by nanoindentation. The elevated hardness may be attributed to the severe lattice distortion and the amorphous structure induced by the Ni addition. Furthermore, microindentation reveals a diversity of deformation behavior in those films with different Ni content. A homogeneous deformation (slight plastic pileup) occurred in the films with Ni content of 1.2 and 4.6, which is close to the deformation behavior of the crystal TiZrNbHf1.6 film. While the film with a Ni content of 1.8 exhibits a catastrophic cracking deformation. Finally, multiple shear banding dominates the deformation of these films with Ni content of 0.4, 2.5 and 3.0. Our findings demonstrate that ultrastrong and highly deformable amorphous high entropy alloy thin films can be developed by appropriate element addition, making them promising materials for corrosion and wear-resistant coatings.