Photoluminescence of a CVD Diamond Excited with VUV Light from a Synchrotron

At the vacuum-ultraviolet (VUV) beam line of a synchrotron, an end station for photoluminescence (PL) coupled to a system to detect absorption is used to investigate the luminescence and absorption of materials. We analyzed a CVD diamond window in wavelength range 160 - 250 nm at 300 and 14 K. The PL excited with VUV light enabled an identification of nitrogen defects in diamond samples. The VUV PL technique is applicable to explore advanced materials including materials with similar wide band gaps, such as boron nitride and aluminum nitride.

In operando-formed interface between silver and perovskite oxide for efficient electroreduction of carbon dioxide to carbon monoxide

Electrochemical carbon dioxide(CO_(2))reduction(ECR)is a promising technology to produce valuable fuels and feedstocks from CO_(2).Despite large efforts to develop ECR catalysts,the investigation of the catalytic performance and electrochemical behavior of complex metal oxides,especially perovskite oxides,is rarely reported.Here,the inorganic perovskite oxide Ag-doped(La_(0.8)Sr_(0.2))_(0.95)Ag_(0.05)MnO_(3-δ)(LSA0.05M)is reported as an efficient electrocatalyst for ECR to CO for the first time,which exhibits a Faradaic efficiency(FE)of 84.3%,a remarkable mass activity of 75Ag^(-1)(normalized to the mass of Ag),and stability of 130 h at a moderate overpotential of 0.79 V.The LSA0.05M catalyst experiences structure reconstruction during ECR,creating the in operando-formed interface between the perovskite and the evolved Ag phase.The evolved Ag is uniformly distributed with a small particle size on the perovskite surface.Theoretical calculations indicate the reconstruction of LSA0.05M during ECR and reveal that the perovskite-Ag interface provides adsorption sites for CO_(2) and accelerates the desorption of the*CO intermediate to enhance ECR.This study presents a novel high-performance perovskite catalyst for ECR andmay inspire the future design of electrocatalysts via the in operando formation of metal-metal oxide interfaces.

Hydrotalcite-wrapped Co–B alloy with enhanced oxygen evolution activity

Water oxidation is one of the most attractive techniques for intermittent renewable energy conversion and storage.The oxygen evolution electrocatalytic performance of an amorphous Co-B alloy and its derivatives were studied.These materials were chemically synthesized by reducing a Co salt with NaBH4.The amorphous Co-B alloy showed good electrocatalytic activity in oxygen evolution but its stability was poor.A hydrotalcite‐wrapped Co-B alloy was synthesized by mild oxidation.The electrocatalytic activity of this material in the oxygen evolution reaction was better than that of a commercially available Ir/C catalyst.

Enabling Extraordinary Rate Performance for Poorly Conductive Oxide Pseudocapacitors

Pseudocapacitive transition metal oxides(PTMOs)have the advantages of high areal capacitance and material density suitable for high-energy supercapacitor devices,but they are typically marred by insufficient rate performance,which in turn deteriorates cyclic stability at high current levels.Using the example of spinel manganese oxide,herein we demonstrate that a pseudocapacitive oxide electrode of remarkable rate performance and cyclic stability may be realized by adopting oxide nanocrystallites,which are derived based on a novel solution chemistry,and carbon additive(CA)nanoparticles with highly uniform of size distributions.Precisely controlling the particle morphology and size distribution of the active material and conductive additive(CA)in the nanometer range can maximize the density of active material-CA-electrolyte three-phase contact points,thus facilitating synchronized electron and cation flow for the completion of surface faradaic reactions.The resultant Mn3O4 pseudocapacitive electrode exhibits rate capability and cycle stability,including 60%capacity retention at 60 A g-1 and no capacity fade over 100000 cycles under dynamic current densities,far superior to the state-of-the-art PTMO electrodes.The electrode design strategy is in general applicable to pseudocapacitors containing poorly conductive active materials.

Synthesis, Composition Optimization, and VUV Photoluminescence Characterization of (Y,Gd)(V,P)O_4∶Eu^(3+) as A Potential Red-Emitting Plasma-Display Panel Phosphor

The synthesis, composition optimization, VUV Photoluminescence (PL) spectra, and optical properties, of (Y,Gd)(V,P)O4∶Eu3+ phosphors were investigated by synchrotron radiation. The VUV PLE spectra and the correlation among VUV PL intensity, λem, and Eu3+, Gd3+, and P-content were established. The PLE spectral studies showed that (Y,Gd)(V,P)O4∶Eu3+ exhibited significant absorption in the VUV range. The VUV PL intensity was found to enhance with PO43- and Gd3+-doping. Furthermore, the chromaticity characteristics of (Y,Gd)(V,P)O4∶Eu3+ were also found to be (0.6614, 0.3286) and compared against (Y, Gd)BO3∶Eu3+ as a reference. Based on the characterization results, we are currently improving and evaluating the potential application of (Y,Gd)(V,P)O4∶Eu3+ as a new red-emitting PDP phosphor.

Vacuum Ultraviolet Spectral Investigations on Green-Emitting Ca(La,Gd)_4Si_3O_(13):Tb^(3+) Phosphors for PDP Applications

In an effort to develop new green-emitting PDP phosphors with high efficiency, investigated were the synthesis, VUV photoluminescence (PL) spectra, optical properties, and chromaticity of Ca(La1-x-yTbxGdy. )4Si3O13 phosphors by using synchrotron radiation. Upon analysis of the VUV spectroscopic and chromaticity investigations on the new greenemitting VUV phosphors, were an optimized composition achieved. The PLE spectral studies show that Ca ( La1-x-y TbxGdy)4Si3O13 exhibit significant absorption in the VUV range. The VUV PL intensity was found to enhance with Gd3+-doping. Furthermore, the 1931 CIE chromaticity coordinates of Ca(La,Gd)4Si3O13:Tb were found to be (0.286, 0.548), as compared to (0.230, 0.712) for Zn2SiP4:Mn2+ as a reference. The potential application of Ca(La,Gd)4Si3O13:Tb as a new green-emitting PDP phosphor are being currently improving and evaluating.

Neutron Spectroscopy Evidence for a Possible Magnetic-Field-Induced Gapless Quantum-Spin-Liquid Phase in a Kitaev Materialα-RuCl3

As one of the most promising Kitaev quantum-spin-liquid(QSL)candidates,α-RuCl_(3)has received a great deal of attention.However,its ground state exhibits a long-range zigzag magnetic order,which defies the QSL phase.Nevertheless,the magnetic order is fragile and can be completely suppressed by applying an external magnetic field.Here,we explore the evolution of magnetic excitations ofα-RuCl;under an in-plane magnetic field,by carrying out inelastic neutron scattering measurements on high-quality single crystals.Under zero field,there exist spin-wave excitations near the M point and a continuum near theΓpoint,which are believed to be associated with the zigzag magnetic order and fractional excitations of the Kitaev QSL state,respectively.By increasing the magnetic field,the spin-wave excitations gradually give way to the continuous excitations.On the verge of the critical fieldμ_(0)H_(c)=7.5 T,the former ones vanish and only the latter ones are left,indicating the emergence of a pure QSL state.By further increasing the field strength,the excitations near theΓpoint become more intense.By following the gap evolution of the excitations near theΓpoint,we are able to establish a phase diagram composed of three interesting phases,including a gapped zigzag order phase at low fields,possibly gapless QSL phase nearμ;H;,and gapped partially polarized phase at high fields.These results demonstrate that an in-plane magnetic field can driveα-RuCl;into a long-sought QSL state near the critical field.

Formation of unusual Cr^5+charge state in CaCr0.5Fe0.5O3 perovskite

A new oxide CaCr0.5Fe0.5O3 was prepared under high pressure and temperature conditions. It crystallizes in a B-site disordered Pbnm perovskite structure. The charge combination is determined to be Cr^5＋/Fe^3＋ with the presence of unusual Cr^5＋ state in octahedral coordination, although Cr^4＋ and Fe^4＋ occur in the related perovskites CaCrO3 and CaFeO3. The randomly distributed Cr^5＋ and Fe^3＋ spins lead to short-range ferromagnetic coupling, whereas an antiferromagnetic phase transition takes place near 50 K due to the Fe^3＋-O-Fe^3＋ interaction. In spite of the B-site Cr^5＋/Fe^3＋ disorder, the compound exhibits electrical insulating behavior. First-principles calculations further demonstrate the formation of CaCr0.5^5＋Fe0.5O3 charge combination, and the electron correlation effect of Fe^3＋ plays an important role for the insulting ground state. CaCr0.5Fe0.5O3 provides the first Cr^5＋ perovskite system with octahedral coordination, opening a new avenue to explore novel transition-metal oxides with exotic charge states.

Antimony oxides-protected ultrathin Ir-Sb nanowires as bifunctional hydrogen electrocatalysts

Developing electrocatalysts with fast kinetics and long-term stability for alkaline hydrogen oxidation reaction(HOR)and hydrogen evolution reaction(HER)is of considerable importance for the industrial production of green and sustainable energy.Here,an ultrathin Ir-Sb nanowires(Ir-Sb NWs)protected by antimony oxides(SbO_(x))was synthesized as an efficient bifunctional catalyst for both HOR and HER under alkaline media.Except from the much higher mass activities of Ir-Sb nanowires than those of Ir nanowires(Ir NWs)and commercial Pt/C,the SbO_(x) protective layer also contributes to the maintenance of morphology and anti-CO poisoning ability,leading to the long-term cycling performance in the presence of CO.Specifically,the Ir-Sb NW/SbO_(x) exhibits the highest catalytic activities,which are about 3.5 and 4.8 times to those of Ir NW/C and commercial Pt/C toward HOR,respectively.This work provides that the ultrathin morphology and H_(2)O-occupied Sb sites can exert the intrinsic high activity of Ir and effectively optimize the absorption of OH*both in alkaline HER/HOR electrolysis.

Understanding synergistic catalysis on Pt–Cu diatomic sites via operando X-ray absorption spectroscopy in sulfur redox reactions

Sulfur redox reactions render lithium–sulfur(Li–S)batteries with an energy density of>500Whkg−1 but suffer a low practical capacity and fast capacity fade due to sluggish sulfur redox reaction(SRR)kinetics,which lies in the complex reaction process that involves a series of reaction intermediates and proceeds via a cascade reaction.Here,we present a Pt–Cu dual-atom catalyst(Pt/Cu-NG)as an electrocatalyst for sulfur redox reactions.Pt/Cu-NG enabled the rapid conversion of soluble polysulfide intermediates into insoluble Li2S2/Li2S,and consequently,it prevented the accumulation and shuttling of lithium polysulfides,thus outperforming the corresponding single-atom catalysts(SACs)with individual Pt or Cu sites.Operando X-ray absorption spectroscopy and density functional theory calculations revealed that a synergistic effect between the paired Pt and Cu atoms modifies the electronic structure of the Pt site through d-orbital interactions,resulting in an optimal moderate interaction of the metal atom with the different sulfide species.This optimal interaction enhanced charge transfer kinetics and promoted sulfur redox reactions.Our work thus provides important insights on the atomic scale into the synergistic effects operative in dual-atom catalysts and will thus pave the way to electrocatalysts with enhanced efficiency for high-performance Li–S batteries.

A comparison study on single metal atoms(Fe,Co,Ni)within nitrogen-doped graphene for oxygen electrocatalysis and rechargeable Zn-air batteries

Single atom catalysts(SACs)with atomically dispersed transition metals on nitrogen-doped carbon supports have recently emerged as highly active non-noble metal electrocatalysts for oxygen reduction reaction(ORR)and oxygen evolution reaction(OER),showing great application potential in Zn-air batteries.However,because of the complex structure-performance relationships of carbon-based SACs in the oxygen electrocatalytic reactions,the contribution of different metal atoms to the catalytic activity of SACs in Zn-air batteries still remains ambiguous.In this study,SACs with atomically dispersed transition metals on nitrogen-doped graphene sheets(M-N@Gs,M=Co,Fe and Ni),featured with similar physicochemical properties and M-N@C configurations,are obtained.By comparing the on-set potentials and the maximum current,we observed that the ORR activity is in the order of Co-N@G>Fe-N@G>Ni-N@G,while the OER activity is in the order of Co-N@G>Ni-N@G>Fe-N@G.The Zn-air batteries with Co-N@G as the air cathode catalysts outperform those with the Fe-N@G and Ni-N@G.This is due to the accelerated charge transfer between Co-N@C active sites and the oxygen-containing reactants.This study could improve our understanding of the design of more efficient bifunctional electrocatalysts for Zn-air batteries at the atomic level.

Neutron diffraction study on anomalous thermal expansion of CrB_(2)

Thermal expansion is an essential issue in the field of materials science and engineering.Investigation of anomalous thermal expansion is beneficial to controlling it and developing related functions.Here,we report disitinctly anisotropic thermal expansion of CrB_(2)via temperature dependence of neutron diffraction,in which positive thermal expansion is observed within basal plane whereas negative thermal expansion emerges along the c direction.Intriguingly,zero thermal expansion of unit cell volume is determined from 5 to 130 K with the coefficient of thermal expansion ofāv=0.4(1)×10^(-6)K^(-1).Magnetization measurement shows there is an antiferromagnetic-paramagnetic transition near 90 K,which may correlate to the thermal expansion anomaly.DFT calculations identify no chemical binding of Cr-Cr pair,implying such antiferromagnetic ordering originates from the double exchange interaction of Cr-B-Cr.

Effect of Laser Welding on Properties of Dissimilar Joint of Al-Mg-Si and Al-Mn Aluminum Alloys

This study discusses the welding properties for the components of an aluminum-alloy ultra-high vacuum chamber and beam position monitor （BPM）.The welding parameters include the modes of laser output （pulsed wave and continuous wave）,welding speed,shield gas flow,welding bead structure,and focusing distance.The results showed that the welding defect rate of the pulsed wave type was larger than that of the continuous wave type.The crack in the welding bead reduced with decreasing welding speed.The fusion penetration of the welding bead was higher when the focusing distance was long enough to deepen into the welding material.Weld morphology during the experimental process revealed the proper flow of shield gas.The adaptability design of the welding bead structure in the preceding processes had more effect on overall welding structure and morphology.

S incorporated RuO_(2)-based nanorings for active and stable water oxidation in acid

The design of highly active and stable RuO_(2)-based nanostructures for acidic oxygen evolution reaction(OER)is extremely important for the development of water electrolysis technology,yet remains great challenges.We here demonstrate that the incorporation of S into RuCuO nanorings(NRs)can significantly enhance the acidic OER performance.Experimental investigations show that the incorporation of S can optimize the interaction of Ru and O,and therefore significantly suppresses the dissolution of Ru in acidic condition.The optimized catalyst(SH-RuCuO NRs)displays superior OER performance to the commercial RuO_(2)/C.Impressively,the SH-RuCuO NRs can exhibit significantly enhanced stability for 3,000 cycles of cyclic voltammetry test and more than 250 h chronopotentiometry test at 10 mA·cm^(-2)in 0.5 M H_(2)SO_(4).This work highlights a potential strategy for designing active and stable RuO_(2)-based electrocatalysts for acidic OER.

Atomically isolated Pd sites within Pd-S nanocrystals enable trifunctional catalysis for direct,electrocatalytic and photocatalytic syntheses of H_(2)O_(2)

Although high-efficiency production of hydrogen peroxide(H_(2)O_(2))can be realized separately by means of direct,electrochemical,and photocatalytic synthesis,developing versatile catalysts is particularly challenging yet desirable.Herein,for the first time we reported that palladium-sulphur nanocrystals(Pd-S NCs)can be adopted as robust and universal catalysts,which can realize the efficient O_(2) conversion by three methods.As a result,Pd-S NCs exhibit an excellent selectivity(89.5%)to H_(2)O_(2)with high productivity(133.6 mol·kgcat^(−1)·h^(−1))in the direct synthesis,along with the significantly enhanced H_(2)O_(2)production activity and stability via electrocatalytic and photocatalytic syntheses.It is demonstrated that the isolated Pd sites can enhance the adsorption of O_(2) and inhibit its O–O bond dissociation,improving H_(2)O_(2)selectivity and reducing H_(2)O_(2)degradation.Further study confirms that the difference in surface atom composition and arrangement is the key factor for different ORR mechanisms on Pd NCs and Pd-S NCs.

Two-dimensional zero thermal expansion in low-cost Mn_(x)Fe_(5−x)Si_(3) alloys via integrating crystallographic texture and magneto-volume effect

Zero thermal expansion(ZTE)alloys have unique aspects in the application of the engineering of precise dimensional control.However,the harsh conditions to realize ZTE,i.e.,appropriate coupling among spin,lattice,and charge upon heating,have limited the ZTE alloys by very few numbers of species.In this work,we report a route to achieving twodimensional(2D)ZTE behavior by regulating crystallographic texture and magneto-volume effects(MVEs)in volumetric positive thermal expansion alloys.This is illustrated in a series of Mn_(x)Fe_(5-x)Si_(3)compounds by those earth-abundant elements.As a result,a 2D ZTE performance with a coefficient of thermal expansion α_(1)=0.45×10^(-7)K^(-1) over a broad temperature window of 10–310 K was observed in MnFe4Si3.The experimental results by synchrotron X-ray diffraction,neutron diffraction,microscopy,and magnetization measurements reveal that such a ZTE behavior is strongly coupled with fiber crystallographic texture and magnetic moment at the crystallographic 6g site that dominates MVEs in the a-b plane.The competition between ferromagnetic Fe_(4d)–Fe_(6g)(J_(FM))and antiferromagnetic Mn_(4d)–Mn_(6g)(J_(AFM))interactions makes the Mn_(1.5)Fe_(3.5)Si_(3) and Mn_(2)Fe_(3)Si_(3)compounds show mixed magnetism and negative thermal expansion(NTE).The integral approach presented here can be used to extend the scope of ZTE/NTE species in other magnetic or ferroelectric materials.

Strong Coupling of Magnetism and Lattice Induces Near-Zero Thermal Expansion over Broad Temperature Windows in ErFe10V2−xMox Compounds

Alloys with low thermal expansion could overcome thermal stress issues under temperature-fluctuated conditions and possess important application prospects,while they are restricted to finite chemical components and temperature windows.In this study,we report a novel class of near-zero thermal expansion(near ZTE)alloys,ErFe_(10)V_(2−x)Mo_(x),over a wide temperature range(120–440 K).Neutron diffraction and magnetic measurements demonstrated that the ErFe_(10)V_(2−x)Mo_(x)compounds exhibited complex ferrimagnetic(FIM)structures below Curie temperature(TC).The near-ZTE behaviors were closely related to the itinerant Fe 3d moments in the collinear FIM states,as well as the geometric[−Fe−Fe−]linkages.Further,X-ray absorption near-edge structure(XANES)spectra revealed that the nonmagnetic substitution changed the electronic valence states of Fe atoms,which,in turn,changed Fe 3d moments and TC,hence,regulating the thermal expansion behaviors.Our work provides an insight into chemical modifications of thermal expansion in magnetic intermetallic compounds.

Characterization and Preparation of Bimetallic Nanoparticles

1 Results Bimetallic particles in the nanometer size range are of substantial interest due to their vast applications in catalysis[1].The synthesis of bimetallic nanoparticles with definite size with a well-control over their nanostructure remains a challenging problem.Thus there exists a great demand for both synthesis and atomic level characterization of nanostructure of bimetallic nanoparticles (NPs).With the recent advent of high-intensity tunable sources of X-rays,now available at synchrotron radia...

High-pressure synthesis,crystal structure and physical properties of a new Cr-based arsenide La3CrAs5

In La-Cr-As system,the first ternary compound La3CrAs5 has been successfully synthesized under highpressure and high-temperature conditions.La3CrAs5 crystallizes into a hexagonal Hf5Sn3Cu-anti type structure with a space group of P63/mcm(No.193)and lattice parameters of a=b=8.9845A and c=5.8897A.The structure contains facesharing octahedral CrAs6 chains along the c-axis,which are arranged triangularly in the ab-plane and separated by a significantly large distance of 8.9845A.The magnetic properties,resistivity and specific heat measurements were performed.La3CrAs5 exhibits a metallic state with Fermi liquid behavior at low temperatures and undergoes a ferromagnetic transition at Curie temperature TC^50 K.First-principles theoretical studies were conducted to calculate its band structure and density of states(DOS),which indicated that the non-negligible contribution of La to the DOS near the Fermi level caused La3CrAs5 to be a three-dimensional(3D)metal.The crystal orbital Hamilton population(-COHP)was also calculated to explain the global stability and bonding characteristics in the structure of La3CrAs5.

Barium hexaferrite/muscovite heteroepitaxy with mechanically robust perpendicular magnetic anisotropy

Recent advances in the design and development of magnetic storage devices have led to an enormous interest in materials with perpendicular magnetic anisotropy(PMA)property.The past decade has witnessed a huge growth in the development of flexible devices such as displays,circuit boards,batteries,memories,etc.since they have gradually made an impact on people’s lives.Thus,the integration of PMA materials with flexible substrates can benefit the development of flexible magnetic devices.In this study,we developed a heteroepitaxy of BaFe_(12)O_(19)(BaM)/muscovite which displays both mechanical flexibility and PMA property.The particular PMA property was characterized by vibrating sample magnetometer,magnetic force microscopy,and x-ray absorption spectroscopy.To quantify the PMA property of the system,the intrinsic magnetic anisotropy energy density of~2.83 Merg cm−3 was obtained.Furthermore,the heterostructure exhibits robust PMA property against severe mechanical bending.The findings of this study on the BaM/muscovite heteroepitaxy have several important implications for research in next-generation flexible magnetic recording devices and actuators.