Pressure-induced stable structures and physical properties of Sr–Ge system

We have systematically investigated the structures of Sr-Ge system under pressures up to 200 GPa and found six stable stoichiometric structures,they being Sr_(3)Ge,Sr_(2)Ge,SrGe,SrGe_(2),SrGe_(3),and SrGe_(4).We demonstrate the interesting structure evolution behaviors in Sr-Ge system with the increase of germanium content,Ge atoms arranging into isolated anions in Sr_(3)Ge,chains in Sr_(2) Ge,square units in SrGe,trigonal units and hexahedrons in SrGe_(2),cages in SrGe_(3),hexagons and Geg rings in SrGe_(4).The structural diversity produces various manifestations of electronic structures,which is of benefit to electrical transportation.Among them,these novel phases with metallic structures show superconductivity(maximum T_(c)~8.94 K for Pmmn Sr_(3)Ge).Notably,the n-type semiconducting Pnma SrGe_(2) structure exhibits high Seebeck coefficient and excellent electrical conductivity along the y direction,leading to a high ZT value up to 1.55 at 500 K,which can be potential candidates as high-performance thermoelectrics.Our results will enable the development of fundamental science in condensed matter physics and potential applications in novel electronics or thermoelectric materials.

Synthesis of Highly Stable One-Dimensional Black Phosphorus/h-BN Heterostructures:A Novel Flexible Electronic Platform

Layered black phosphorus(BP)has recently emerged as a promising semiconductor because of its tunable band gap,high carrier mobility and strongly in-plane anisotropic properties.One-dimensional(1 D)BP materials are attractive for applications in electronic and thermal devices,owing to their tailored charge and phonon transports along certain orientations.However,the fabrication of 1 D BP materials still remains elusive thus far.We herein report the successful synthesis and characterization of nanotube-like BP for the first time by a selective composite with hexagonal boron nitride(h-BN)nanotubes under high pressure and high temperature conditions.The produced 1 D BP/h-BN composites possess flexible diameter,length and thickness by adjusting the experimental synthesis parameters.Interestingly,it is important to notice that the stability of our BP sample has been significantly improved under the formation of heterostructures,which can actively promote their commercial applications.Our experimental work,together with first-principles calculations,presents a new scalable strategy of designing 1 D tube-like BP/h-BN heterostructures that are promising candidates for flexible and high efficiency electronic platform.

Clathrate structure of YB_(3)C_(3) for high-performance thermoelectrics with superior mechanical properties

Exploring high-performance thermoelectric materials with improved mechanical properties is important for broadening the application scope and the assembly requirement of stable devices.This work presents an effective strategy to discover hard thermoelectric material by inserting foreign atoms in the rigid covalent framework.We demonstrate this in boron-carbon clathrate VII structure,showing a promising candidate for highly efficient thermoelectric energy conversion,especially with Y atom filled in the cage,with a peak zT of 0.73 at 1,000 K.The ab initio calculations indicate that YB_(3)C_(3) system has low lattice thermal conductivity of 4.5 W/(m·K)at 1,000 K due to the strong rattling of encaged Y atom.The strongly covalent framework provides highly degenerate band structures consisting of heavy and light electron pockets,which can maintain high carrier mobility arising from small effective mass and thus large group velocity.Consequently,high power factor can be achieved in YB_(3)C_(3) for both electron and hole doping.In addition,it exhibits well mechanical properties and a Vickers hardness of 23.7 GPa because of the strong covalent boron-carbon framework.This work provides a novel avenue for the search of high-performance thermoelectric materials with excellent mechanical properties,based on boron-carbon clathrate structure.

Screening for new thermoelectric material: A semiconducting TaS_(3) with nanoporous structure

Transition-metal sulfides,such as 1T-and 2H-TaS_(2),are attracting considerable interest in modern condensed matter physics for their diverse behaviors of the Mott state,peculiar charge-density-wave phase and superconductivity.The intrinsically low thermal conductivities along the cross-plane direction can advantage the potential high thermoelectric performance;yet,their insignificant power factors severely hampered the practical applications as thermoelectric devices.In this perspective,we herein present a new semiconducting phase in TaS_(3) with the space group C2/m predicted by the swarmintelligence structure-searching method.The C2/m-TaS_(3) phase exhibits anisotropic multivalley band dispersions,which is beneficial for electronic transport.Meanwhile,the unique structure within nanopores leads to strong anharmonic scattering,significantly reducing the lattice thermal conductivity.As a result,the calculated figure of merit ZT can reach up to 1.68 and 1.57 at 800 K for p-and n-type,respectively that is comparable with conventional thermoelectric materials(e.g.PbTe,Bi_(2)Te_(3)).Therefore,our calculation reveals that the C2/m-TaS_(3) phase can be a potential high-performance candidate as nontoxic and eco-friendly thermoelectrics,and will stimulate further experimental exploration for understanding and tailoring thermoelectric capability in related transition-metal sulfides.