Superconductivity in the Layered Cage Compound Ba_(3)Rh_(4)Ge_(16)

We report the synthesis and superconducting properties of a layered cage compound Ba_(3)Rh_(4)Ge_(16).Similar to Ba_(3)Ir_(4)Ge_(16),the compound is composed of 2 D networks of cage units,formed by noncubic Rh-Ge building blocks,in marked contrast to the reported rattling compounds.The electrical resistivity,magnetization,specific heat capacity,andμSR measurements unveiled moderately coupled s-wave superconductivity with a critical temperature T_(c)=7.0 K,the upper critical field μ_(0)H_(c2)(0)~2.5 T,the electron-phonon coupling strength λ_(e-ph)~0.80,and the Ginzburg-Landau parameterκ~7.89.The mass reduction with the substitution of Ir by Rh is believed to be responsible for the enhancement of T_(c) and coupling between the cage and guest atoms.Our results highlight the importance of atomic weight of framework in cage compounds in controlling the λ_(e-ph) strength and T_(c).

Pressure-Induced Topological and Structural Phase Transitions in an Antiferromagnetic Topological Insulator

Recently,natural van der Waals heterostructures of(MnBi2 Te4)m(Bi2 Te3)n have been theoretically predicted and experimentally shown to host tunable magnetic properties and topologically nontrivial surface states.We systematically investigate both the structural and electronic responses of MnBi2 Te4 and MnBi4 Te7 to external pressure.In addition to the suppression of antiferromagnetic order,MnBi2 Te4 is found to undergo a metalsemiconductor-metal transition upon compression.The resistivity of MnBi4 Te7 changes dramatically under high pressure and a non-monotonic evolution of p(T)is observed.The nontrivial topology is proved to persist before the structural phase transition observed in the high-pressure regime.We find that the bulk and surface states respond differently to pressure,which is consistent with the non-monotonic change of the resistivity.Interestingly,a pressure-induced amorphous state is observed in MnBi2 Te4,while two high-pressure phase transitions are revealed in MnBi4 Te7.Our combined theoretical and experimental research establishes MnBi2 Te4 and MnBi4 Te7 as highly tunable magnetic topological insulators,in which phase transitions and new ground states emerge upon compression.

Robust two-gap strong coupling superconductivity associated with low-lying phonon modes in pressurized Nb5Ir3O superconductors

We report robust superconducting state and gap symmetry of Nb5Ir3O via electrical transport and specific heat measurements. The analysis of specific heat manifests that Nb5Ir3O is a strongly coupled superconductor with ΔC/γnTc ~ 1.91 and double s-wave superconducting gaps of 2ΔL(0)/kBTc ~ 6.56 and 2ΔS(0)/kBTc ~ 2.36 accounting for 90% and 10%,respectively. The(Cp-γnT)/T^3 vs. T plot shows a broad peak at ~ 23 K, indicating phonon softening and the appearance of low-lying phonon mode associated with the interstitial oxygen. This behavior explains the monotonic increase of Tc in Nb5Ir3O(1-δ)by strengthening the electron-phonon coupling and enlarging the density of states at Fermi level. The Hall coefficient is temperature independent below 200 K, and changes its sign from positive to negative above 250 K, suggesting that carrier is across the hole-to electron-dominant regions and the multi-band electronic structures. On warming, the resistivity shows a gradual crossover from T^2-to T^3-dependence at a critical temperature T^*, and a broad peak at a temperature Tp. The reduced Tc under pressure is linearly correlated with lattice parameters c/a ratio and Tp, suggesting the important phonon contributions in Nb5Ir3O as a phonon-medicated superconductor. Possible physical mechanisms are proposed.

Pressure-induced reemergence of superconductivity in BaIr_(2)Ge_(7)and Ba_(3)Ir_(4)Ge_(16)with cage structures

Clathrate-like or caged compounds have attracted great interest owing to their structural flexibility,as well as their fertile physical properties.Here,we report the pressure-induced reemergence of superconductivity in BaIr2Ge7 and Ba3Ir4Ge16,two new caged superconductors with two-dimensional building blocks of cage structures.After suppression of the ambient-pressure superconducting(SC-I)states,new superconducting(SC-II)states emerge unexpectedly,with Tc increased to a maximum of 4.4 and 4.0 K for BaIr2Ge7 and Ba3Ir4Ge16,respectively.Combined with high-pressure synchrotron x-ray diffraction and Raman measurements,we propose that the reemergence of superconductivity in these caged superconductors can be ascribed to a pressure-induced phonon softening linked to cage shrinkage.

电磁场辅助绿色氨合成

Nitrogen is an indispensable element for life because it is a constituent of amino acids and a key constituent for various materials,as well as fine chemicals.Nitrogen molecules occupy~80%of the atmosphere but are chemically inert due to the strength of the NN triple bond and absence of polarity.This nonpolar nature makes N_(2)totally different from CO with an isoelectronic diatomic structure in reactivity.Thus,it was a challenge in chemistry to activate N_(2)to transform it into chemically usable molecules,such as NH_(3)and NO_(x).The Haber-Bosch(HB)process for the synthesis of NH_(3)from N_(2)and H_(2),which was established in 1913,marked the first practical chemical process of nitrogen fixation through extensive fundamental chemical research and much engineering ingenuity[1,2].This success of the industrial process saves human civilization from a hunger crisis.Since then,the HB process has been the predominant method for industrial NH_(3)production.The annual NH_(3)production has reached180 million tons globally,which makes it the most mass-produced chemical comparable to methanol.

Synthesis of stable iodoplumbate and perovskite for efficient annealing-free device and long-term storage

As a next-generation photovoltaic device,perovskite solar cells are rapidly emerging.Nevertheless,both solution and device stability pose challenges for commercialization due to chemical degradation caused by internal and external factors.Especially,the decomposition of iodoplumbate in a perovskite solution hinders the long-term use of perovskite solutions.Moreover,the synthesis of stable perovskites at low temperature is important for stable devices and wide applications(flexible devices and high reproducibility).Herein,the critical composition of perovskite is found to obtain high stabilities of both iodoplumbate and perovskite crystals by utilizing CsPbBr_(3) and FAPbI_(3),exhibiting high device performance and long-term solution storage.The novel composition of CsPbBr_(3)-alloyed FAPbI_(3) not only crystallizes under annealing-free conditions but also demonstrates excellent iodoplumbate stability for 100 days(∼3000 h)without any degradation.Furthermore,high device stabilities are achieved over 2000 and 3000 h under extreme conditions of A.M.1.5 and 85℃/85%relative humidity,respectively.Overall,the device exhibited a high power conversion efficiency of 23.4%,and furthermore,CsPbBr_(3)-alloyed FAPbI_(3) was devoted to widen the applications in both flexible and carbon-electrode devices,thereby addressing both scientific depths and potential commercial materials.

Large magnetocaloric effect in van der Waals crystal CrBr3

We study the magnetocaloric effect (MCE) in van der Waals (vdW) crystal CrBr3.Bulk CrBr3 exhibits a second-order paramagnetic-ferromagnetic phase transition with TC =33 K.The maximum magnetic entropy change-△SM near TC is about 7.2 J.kg-1.K-1 with the maximum adiabatic temperature change △Tadmax =2.37 K and the relative cooling power RCP =191.5 J.kg-1 at μoH =5 T,all of which are remarkably larger than those in CrI3.These results suggest that the vdW crystal CrBr3 is a promising candidate for the low-dimensional magnetic refrigeration in low temperature region.

Superconductivity induced by field-driven proton injection

Doping is a key operation to induce superconductivity.Parent materials do not exhibit superconductivity in most cases of high Tcsystems but convert into superconductor when carriers are doped.Doping of impurity diminishes the long range ordering of spin,charge and/or orbitals,and superconductivity emerges in the neighbor of boundary between ordered and non-ordered phases.The parent phase of high-Tccuprate superconductors

一种新型超导母体:褶皱的蜂窝状空位有序

空位在材料体系中无处不在,空位的存在也极大地影响了材料的光学、热学、电学等性质.目前,空位的研究主要集中在弱关联的体系,而在强关联体系中的空位以及空位和其他新奇量子现象的关系则知之甚少.本文在强关联铱化物Ir16Sb18中发现了一种新奇的空位有序:褶皱的蜂窝状空位序.理论计算表明实空间的空位有序来源于倒空间的费米面嵌套,而空位有序的形成破坏了对称性,使得费米面附近的电子局域化.通过在空位中引入Ir或者用Rh来替代Ir,可以有效地破坏空位有序从而引入超导电性.空位有序与超导电性的竞争关系表明:具有褶皱的蜂窝状空位有序的Ir16Sb18是一种新型的超导母体.这种独特的褶皱蜂窝状空位有序,及其实空间-倒空间的关系,表明了"关联空位"的重要性,这为探索更多新奇量子临界现象带来契机.

Insight into rare-earth-incorporated catalysts:The chance for a more efficient ammonia synthesis

Recent studies have suggested that rare earth(RE)elements in catalysts significantly influence the performance of the ammonia synthesis.The REs appear in various forms in the ammonia synthesis catalysts including supports(oxides,hydrides,and nitrides),promotors,and intermetallic.Besides the conventional RE oxide-supporting catalysts(mainly Ru/REO),some new RE-containing catalyst systems,such as electrode and nitride systems,could drive the ammonia synthesis via a benign Mars-van Krevelen mechanism or multi-active-site mode,affording high ammonia synthesis performance under mild conditions.These works demonstrate the great potential of RE-containing catalysts for more efficient ammonia synthesis.This review summarizes the contributions of different kinds of RE-based catalysts and highlights the function mechanism of incorporated REs.Finally,an overview of this area and the challenges for further investigation are provided.

Crystal and electronic structure engineering of tin monoxide by external pressure

Although tin monoxide (SnO) is an interesting compound due to its p-type conductivity,a widespread application of SnO has been limited by its narrow band gap of 0.7 eV.In this work,we theoretically investigate the structural and electronic properties of several SnO phases under high pressures through employing van der Waals (vdW) functionals.Our calculations reveal that a metastable SnO (β-SnO),which possesses space group P2_(1)/c and a wide band gap of 1.9 eV,is more stable than α-SnO at pressures higher than 80 GPa.Moreover,a stable (space group P2/c) and a metastable (space group Pnma) phases of SnO appear at pressures higher than 120 GPa.Energy and topological analyses show that P2/c-SnO has a high possibility to directly transform to β-SnO at around 120 GPa.Our work also reveals that β-SnO is a necessary intermediate state between high-pressure phase Pnma-SnO and low-pressure phase α-SnO for the phase transition path Pnma-SnO →β-SnO →α-SnO.Two phase transition analyses indicate that there is a high possibility to synthesize β-SnO under high-pressure conditions and have it remain stable under normal pressure.Finally,our study reveals that the conductive property of β-SnO can be engineered in a low-pressure range (0-9 GPa)through a semiconductor-to-metal transition,while maintaining transparency in the visible light range.

Identifying quasi-2D and 1D electrides in yttrium and scandium chlorides via geometrical identification

Developing and understanding electron-rich electrides offers a promising opportunity for a variety of electronic and catalytic applications.Using a geometrical identification strategy,here we identify a new class of electride material,yttrium/scandium chlorides Y(Sc)_(x)Cl_(y)(yx<2).Anionic electrons are found in the metal octahedral framework topology.The diverse electronic dimensionality of these electrides is quantified explicitly by quasi-two-dimensional(2D)electrides for[YCl]^(+)∙e−and[ScCl]^(+∙)e−and one-dimensional(1D)electrides for[Y_(2)Cl_(3)]^(+)∙e−,[Sc_(7)Cl_(10)]^(+)∙e−,and[Sc5Cl8]2+∙2e−with divalent metal elements(Sc^(2+):3d^(1) and Y^(2+):4d^(1)).The localized anionic electrons were confined within the inner-layer spaces,rather than inter-layer spaces that are observed in A_(2)B-type 2D electrides,e.g.Ca_(2)N.Moreover,when hydrogen atoms are introduced into the host structures to form YClH and Y2Cl3H,the generated phases transform to conventional ionic compounds but exhibited a surprising reduction of work function,arising from the increased Fermi level energy,contrary to the conventional electrides reported so far.Y_(2C)l_(3) was experimentally confirmed to be a semiconductor with a band gap of 1.14 eV.These results may help to promote the rational design and discovery of new electride materials for further technological applications.