查看更多>>摘要：The Chinese Bayan Obo deposit is a world-class rare earth element(REE)deposit with considerable niobium(Nb)and iron(Fe)resources.A complete genetic understanding on all metals is fundamental for establishing genetic models at Bayan Obo.With extensive research being focused on REE enrichment,the timing and controls of Nb enrichment remain unresolved at Bayan Obo,which is mainly due to the challenges in dating,i.e.multistage thermal events,fine-grained minerals with complex textures and the rare occurrence of uranium-enriched minerals with mature dating methods.Based on robust geological and petrographic frameworks,here we conducted ion probe uranium-lead(U-Pb)dating of ferrocolumbite to unravel the timing,hence the genesis of Nb mineralization.Three types of hydrothermal ferrocolumbites—key Nb-bearing minerals—are identified based on their textures and mineral assemblages.They yield U-Pb ages of 1312±47 Ma(n=99),438±7 Ma(n=93),and 268±5 Ma(n=19),respectively.In line with deposit geology,we tentatively link the first,second and third stage Nb mineralization to Mesoproterozoic carbonatite magmatism,ubiquitous early Paleozoic hydrothermal activity,and Permian granitic magmatism,respectively.While quantifying the contribution of metal endowment from each stage requires further investigation,our new dates highlight that multi-stage mineralization is critical for Nb enrichment at Bayan Obo,which may also have implications for the enrichment mechanism of Nb in REE deposits in general.
查看更多>>摘要：Neural operators have been explored as surrogate models for simulating physical systems to overcome the limitations of traditional partial differential equation(PDE)solvers.However,most existing operator learning methods assume that the data originate from a single physical mechanism,limiting their applicability and performance in more realistic scenarios.To this end,we propose the physical invariant attention neural operator(PIANO)to decipher and integrate the physical invariants for operator learning from the PDE series with various physical mechanisms.PIANO employs self-supervised learning to extract physical knowledge and attention mechanisms to integrate them into dynamic convolutional layers.Compared to existing techniques,PIANO can reduce the relative error by 13.6％-82.2％on PDE forecasting tasks across varying coefficients,forces or boundary conditions.Additionally,varied downstream tasks reveal that the PI embeddings deciphered by PIANO align well with the underlying invariants in the PDE systems,verifying the physical significance of PIANO.
查看更多>>摘要：Iron-metal clusters are crucial in a variety of critical biological and material systems,including metalloenzymes,catalysts,and magnetic storage devices.However,a synthetic high-nuclear iron cluster has been absent due to the extreme difficulty in stabilizing species with direct iron-iron bonding.In this work,we have synthesized,crystallized,and characterized a(Tp*)4W4S12(Fe@Fe12)cluster(Tp*=tris(3,5-dimethyl-l-pyrazolyl)borate(1-)),which features a rare trideca-nuclear,icosahedral[Fe@Fe12]cluster core with direct multicenter iron-iron bonding between the interstitial iron(Fei)and peripheral irons(Fep),as well as Fep…Fep ferromagnetic coupling.Quantum chemistry studies reveal that the stability of the cluster arises from the 18-electron shell-closing of the[Fe@Fe 12]16+core,assisted by its bonding interactions with the peripheral tridentate[(Tp*)WS3]4-ligands which possess both S→Fe donation and spin-polarized Fe-W σ bonds.The ground-state electron spin is theoretically predicted to be S=32/2 for the cluster.The existence of low oxidation-state(OS～+1.23)iron in this compound may find interesting applications in magnetic storage,spintronics,redox chemistry,and cluster catalysis.
查看更多>>摘要：The absence of efficient and durable catalysts for oxygen evolution reaction(OER)is the main obstacle to hydrogen production through water splitting in an acidic electrolyte.Here,we report a controllable synthesis method of surface IrOx with changing Au/Ir compositions by constructing a range of sub-10-nm-sized core-shell nanocatalysts composed of an Au core and AuxIr1-x alloy shell.In particular,Au@Au0.43Ir0.57 exhibits 4.5 times higher intrinsic OER activity than that of the commercial Ir/C.Synchrotron X-ray-based spectroscopies,electron microscopy and density functional theory calculations revealed a balanced binding of reaction intermediates with enhanced activity.The water-splitting cell using a load of 0.02 mgIr/cm2 of Au@Au0.43Ir0.57 as both anode and cathode can reach 10 mA/cm2 at 1.52 V and maintain activity for at least 194 h,which is better than the cell using the commercial couple Ir/C ||Pt/C(1.63 V,0.2 h).
查看更多>>摘要：The water oxidation half-reaction at anodes is always considered the rate-limiting step of overall water splitting(OWS),but the actual bias distribution between photoanodes and cathodes of photoelectrochemical(PEC)OWS cells has not been investigated systematically.In this work,we find that,for PEC cells consisting of photoanodes(nickel-modified n-Si[Ni/n-Si]and α-Fe2O3)with low photovoltage(Vph＜1V),a large portion of applied bias is exerted on the Pt cathode for satisfying the hydrogen evolution thermodynamics,showing a thermodynamics-controlled characteristic.In contrast,for photoanodes(TiO2 and BiVO4)with Vph＞1V,the bias required for cathode activation can be significantly reduced,exhibiting a kinetics-controlled characteristic.Further investigations show that the bias distribution can be regulated by tuning the electrolyte pH and using alternative half-reaction couplings.Accordingly,a volcano plot is presented for the rational design of the overall reactions and unbiased PEC cells.Motivated by this,an unbiased PEC cell consisting of a simple Ni/n-Si photoanode and Pt cathode is assembled,delivering a photocurrent density of 5.3±0.2 mA cm-2.
查看更多>>摘要：Zeolitic imidazolate frameworks(ZIFs)feature complex phase transitions,including polymorphism,melting,vitrification,and polyamorphism.Experimentally probing their structural evolution during transitions involving amorphous phases is a significant challenge,especially at the medium-range length scale.To overcome this challenge,here we first train a deep learning-based force field to identify the structural characteristics of both crystalline and non-crystalline ZIF phases.This allows us to reproduce the structural evolution trend during the melting of crystals and formation of ZIF glasses at various length scales with an accuracy comparable to that of ab initio molecular dynamics,yet at a much lower computational cost.Based on this approach,we propose a new structural descriptor,namely,the ring orientation index,to capture the propensity for crystallization of ZIF-4(Zn(Im)2,Im=C3H3N2-)glasses,as well as for the formation of ZIF-zni(Zn(Im)2)out of the high-density amorphous phase.This crystal formation process is a result of the reorientation of imidazole rings by sacrificing the order of the structure around the zinc-centered tetrahedra.The outcomes of this work are useful for studying phase transitions in other metal-organic frameworks(MOFs)and may thus guide the development of MOF glasses.
查看更多>>摘要：The short-range order and medium-range order of amorphous carbons demonstrated in experiments allow us to rethink whether there exist intrinsic properties hidden by atomic disordering.Here we presented six representative phases of amorphous carbons(0.1-3.4 g/cm3),namely,disordered graphene network(DGN),high-density amorphous carbon(HDAC),amorphous diaphite(a-DG),amorphous diamond(a-D),paracrystalline diamond(p-D),and nano-polycrystalline diamond(NPD),respectively,classified by their topological features and microstructural characterizations that are comparable with experiments.To achieve a comprehensive physical landscape for amorphous carbons,a phase diagram was plotted in the sp3/sp2 versus density plane,in which the counterintuitive discontinuity originates from the inherent difference in topological microstructures,further guiding us to discover a variety of phase transitions among different amorphous carbons.Intriguingly,the power law,log(sp3/sp2)∝ pn,hints at intrinsic topology and hidden order in amorphous carbons,providing an insightful perspective to reacquaint atomic disorder in non-crystalline carbons.
查看更多>>摘要：Solid solutions are ubiquitous in metals and alloys.Local chemical ordering(LCO)is a fundamental sub-nano/nanoscale process that occurs in many solid solutions and can be used as a microstructure to optimize strength and ductility.However,the formation of LCO has not been fully elucidated,let alone how to provide efficient routes for designing LCO to achieve synergistic effects on both superb strength and ductility.Herein,we propose the formation and control of LCO in negative enthalpy alloys.With engineering negative enthalpy in solid solutions,genetic LCO components are formed in negative enthalpy refractory high-entropy alloys(RHEAs).In contrast to conventional'trial-and-error'approaches,the control of LCO by using engineering negative enthalpy in RHEAs is instructive and results in superior strength(1160 MPa)and uniform ductility(24.5％)under tension at ambient temperature,which are among the best reported so far.LCO can promote dislocation cross-slip,enhancing the interaction between dislocations and their accumulation at large tensile strains;sustainable strain hardening can thereby be attained to ensure high ductility of the alloy.This work paves the way for new research fields on negative enthalpy solid solutions and alloys for the synergy of strength and ductility as well as new functions.
查看更多>>摘要：Tracking the dynamic surface evolution of metal halide perovskite is crucial for understanding the corresponding fundamental principles of photoelectric properties and intrinsic instability.However,due to the volatility elements and soft lattice nature of perovskites,several important dynamic behaviors remain unclear.Here,an ultra-high vacuum(UHV)interconnection system integrated by surface-sensitive probing techniques has been developed to investigate the freshly cleaved surface ofCH3NH3PbBr3 in situ under given energy stimulation.On this basis,the detailed three-step chemical decomposition pathway of perovskites has been clarified.Meanwhile,the evolution of crystal structure from cubic phase to tetragonal phase on the perovskite surface has been revealed under energy stimulation.Accompanied by chemical composition and crystal structure evolution,electronic structure changes including energy level position,hole effective mass,and Rashba splitting have also been accurately determined.These findings provide a clear perspective on the physical origin of optoelectronic properties and the decomposition mechanism of perovskites.
查看更多>>摘要：Due to their uncontrollable assembly and crystallization process,the synthesis of mesoporous metal oxide single crystals remains a formidable challenge.Herein,we report the synthesis of single-crystal-like mesoporous Li2TiSiOs by using soft micelles as templates.The key lies in the atomic-scale self-assembly and step-crystallization processes,which ensure the formation of single-crystal-like mesoporous Li2TiSiO5 microparticles via an oriented attachment growth mechanism under the confinement of an in-situ formed carbon matrix.The mesoporous Li2TiSiO5 anode achieves a superior rate capability(148 mAh g-1 at 5.0 A g-1)and outstanding long-term cycling stability(138 mAh g-1 after 3000 cycles at 2.0 A g-1)for lithium storage as a result of the ultrafast Li+diffusion caused by penetrating mesochannels and nanosized crystal frameworks(5-10 nm).In comparison,bulk Li2TiSiO5 exhibits poor rate capability and cycle performance due to micron-scale diffusion lengths.This method is very simple and reproducible,heralding a new way of designing and synthesizing mesoporous single crystals with controllable frameworks and chemical functionalities.
NETL
NSTL
万方数据