Strong electron correlation-induced Mott-insulating electrides of Ae_(5)X_(3)(Ae=Ca,Sr,and Ba;X=As and Sb)

The presence of interstitial electrons in electrides endows them with interesting attributes,such as low work function,high carrier concentration,and unique magnetic properties.Thorough knowledge and understanding of electrides are thus of both scientific and technological significance.Here,we employ first-principles calculations to investigate Mott-insulating Ae_(5)X_(3)(Ae=Ca,Sr,and Ba;X=As and Sb)electrides with Mn_(5)Si_(3)-type structure,in which half-filled interstitial electrons serve as ions and are spin-polarized.The Mott-insulating property is induced by strong electron correlation between the nearest interstitial electrons,resulting in spin splitting and a separation between occupied and unoccupied states.The half-filled antiferromagnetic configuration and localization of the interstitial electrons are critical for the Mott-insulating properties of these materials.Compared with that in intermetallic electrides,the orbital hybridization between the half-filled interstitial electrons and the surrounding atoms is weak,leading to highly localized magnetic centers and pronounced correlation effects.Therefore,the Mott-insulating electrides Ae_(5)X_(3)have very large indirect bandgaps(0.30 eV).In addition,high pressure is found to strengthen the strong correlation effects and enlarge the bandgap.The present results provide a deeper understanding of the formation mechanism of Mott-insulating electrides and provide guidance for the search for new strongly correlated electrides.

Synergistic influences of titanium,boron,and oxygen on large-size single-crystal diamond growth at high pressure and high temperature

The synergistic influences of boron,oxygen,and titanium on growing large single-crystal diamonds are studied using different concentrations of B_(2)O_(3) in a solvent-carbon system under 5.5 GPa-5.7 GPa and 1300℃-1500℃.It is found that the boron atoms are difficult to enter into the crystal when boron and oxygen impurities are doped using B_(2)O_(3) without the addition of Ti atoms.However,high boron content is achieved in the doped diamonds that were synthesized with the addition of Ti.Additionally,boron-oxygen complexes are found on the surface of the crystal,and oxygen-related impurities appear in the crystal interior when Ti atoms are added into the FeNi-C system.The results show that the introduction of Ti atoms into the synthesis cavity can effectively control the number of boron atoms and the number of oxygen atoms in the crystal.This has important scientific significance not only for understanding the synergistic influence of boron,oxygen,and titanium atoms on the growth of diamond in the earth,but also for preparing the high-concentration boron or oxygen containing semiconductor diamond technologies.

High-pressure electrides: From design to synthesis

Electrides are unique ionic compounds that electrons serve as the anions. Many electrides with fascinating physical and chemical properties have been discovered at ambient condition. Under pressure, electrides are also revealed to be ubiquitous crystal morphology, enriching the geometrical topologies and electronic properties of electrides. In this Review,we overview the formation mechanism of high-pressure electrides(HPEs) and outline a scheme for exploring new HPEs from pre-design, CALYPSO assisted structural searches, indicators for electrides, to experimental synthesis. Moreover, the evolution of electronic dimensionality under compression is also discussed to better understand the dimensional distribution of anionic electrons in HPEs.

Properties of B4C-TiB2 ceramics prepared by spark plasma sintering

By doping titanium hydride(TiH2) into boron carbide(B4C), a series of B4C + x wt% TiH2(x = 0, 5, 10, 15, and 20)composite ceramics were obtained through spark plasma sintering(SPS). The effects of the sintering temperature and the amount of TiH2 additive on the microstructure, mechanical and electrical properties of the sintered B4C-TiB2 composite ceramics were investigated. Powder mixtures of B4C with 0–20 wt% TiH2 were heated from 1400℃ to 1800℃ for 20 min under 50 MPa. The results indicated that higher sintering temperatures contributed to greater ceramic density. With increasing TiH2 content, titanium diboride(TiB2) formed between the TiH2 and B4C matrix. This effectively improved Young’s modulus and fracture toughness of the composite ceramics, significantly improving their electrical properties: the electrical conductivity reached 114.9 S·cm-1 at 1800℃ when x = 20. Optimum mechanical properties were obtained for the B4C ceramics sintered with 20 wt% TiH2, which had a relative density of 99.9±0.1%, Vickers hardness of 31.8 GPa,and fracture toughness of 8.5 MPa·m1/2. The results indicated that the doping of fine Ti particles into the B4C matrix increased the conductivity and the fracture toughness of B4C.

Stabilizing n-type cubic AgBiSe_(2) thermoelectric materials through alloying with PbS

Phase transition generates rapid changes of transport parameters and poor mechanical property,and thus restricts the application of thermoelectric materials.AgBiSe_(2) exhibits cubic phase at above 580 K with high-symmetry structure and low lattice thermal conductivity,indicating the potentiality of high thermoelectric performances.In this work,the cubic structure of AgBiSe_(2) was achieved at ambient conditions by alloying with PbS,enhancing the configurational entropy at both cationic and anionic sites.The cubic structure was rather stable after several measurement cycles.Nb substitution at cationic sites effectively reduced band gap,and increased both carrier concentration and effective mass.All samples exhibited relatively low lattice thermal conductivity(0.68-0.34 W/(m·K))in the temperature range of 300-773 K,due to the nanoscale inhomogeneity and the random distribution of multiple species at some atomic sites.A maximum zT of 0.65 at 773 K was obtained for(Ag_(0.99)Nb_(0.01)BiSe_(2))_(0.8)(PbS)_(0.2) sample.The entropy-driven structural stabilization is a promising strategy to achieve stable structure for practical thermoelectric applications.

Thermoelectric properties of n-type SiGe alloys with Sn incorporation

In the past several decades,silicon germanium(SiGe)bulk alloys have been a research focus in addressing the current global energy crisis and environmental pollution problems due to their excellent high-temperature thermoelectric properties.In this study,n-type Si_(80)Ge_(20)P_(2)Sn_(x)bulk alloys were fabricated by spark plasma sintering(SPS)to investigate the effect of Sn incorporation.In addition,the optimal sintering conditions and Sn content were determined.The introduction of Sn improves the electrical conductivity and power factor of the n-type SiGe bulk alloys due to the doping and composite effects.Particularly,the Si_(80)Ge_(20)P_(2)Sn_(2)bulk alloy could reach a high figure of merit(ZT)value of~1.26 at 800℃.Thus,this work provides a quick preparation method for obtaining n-type SiGe bulk alloys with outstanding thermoelectric properties by incorporating Sn,which is favorable for large-scale production.

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.

Interactions of organic phosphorus with soil minerals and the associated environmental impacts: A review

As an important part of the soil phosphorus(P)pool,organic P(OP)is widely found in terrestrial and aquatic environments(e.g.,soils and sediments).The interfacial behavior of OP on natural minerals affects the transport,transformation,and bioavailability of P in the environment.This paper reviews the processes involving adsorption-desorption,dissolution-precipitation,and enzymatic/mineral-mediated hydrolysis of OP at the mineral-water interface,and their subsequent effects on OP speciation and mineral colloidal stability/reactivity.The sorption mechanisms of OP on natural minerals mainly include surface complexation and precipitation,which are controlled by factors such as mineral identity and crystallinity,the relative molecular weight of OP,reaction pH,ionic strength,temperature,and co-existing ligands or ions.The desorption amount and rate of OP from minerals are determined by the mineral identity,desorbent type,pre-sorption time,OP species,reaction pH,number of desorption cycles,and redox status.The interactions between OP and minerals affect the sorption of co-existing metal ions and the stability of the minerals.The effect of minerals on the enzymatic hydrolysis of OP sorbed on mineral surfaces depends on the mineral identity and OP species.Some minerals also exhibit catalytic activity to promote the cleavage of C–O–P bonds and OP hydrolysis.We provide an overview of state-of-the-art techniques currently applied in environmental OP research.The main challenges and future research directions are also summarized to further explore OP interactions with natural minerals in complex environmental settings.

Simultaneous oxidation of Mn (Ⅱ) and As (Ⅲ) on cupric oxide (CuO) promotes As (Ⅲ) removal at circumneutral pH

Oxidation of Mn (Ⅱ) or As(Ⅲ) by molecular oxygen is slow at pH<9,while they can be catalytically oxidized in the presence of oxide minerals and then removed from contaminated water.However,the reaction mechanisms on simultaneous oxidation of Mn(Ⅱ) and As (Ⅲ)on oxide mineral surface and their accompanied removal efficiency remain unclear.This study compared Mn (Ⅱ) oxidation on four common metal oxides (γ-Al_(2)O_(3),CuO,α-Fe2O_(3)and ZnO) and investigated the simultaneous oxidation and removal of Mn (Ⅱ) and As (Ⅲ) through batch experiments and spectroscopic analyses.Among the tested oxides,CuO and α-Fe2O_(3)possess greater catalytic activity toward Mn (Ⅱ) oxidation.Oxidation and removal kinetics of Mn (Ⅱ) and As (Ⅲ) on CuO indicate that O_(2)is the terminal electron acceptor for Mn (Ⅱ) and As (Ⅲ) oxidation on CuO,and Mn (Ⅱ) acts as an electron shuttle to promote As (Ⅲ) oxidation and removal.The main oxidized product of Mn (Ⅱ) on CuO is high-valent MnO_(x)species.This newly formed Mn (Ⅲ) or Mn (IV) phases promote As (Ⅲ) oxidation on CuO at circumneutral pH 8 and is reduced to Mn (Ⅱ),which may be then released into solution.This study provides new insights into metal oxide-catalyzed oxidation of pollutants Mn (Ⅱ) and As (Ⅲ) and suggests that CuO should be considered as an efficient material to remediate Mn (Ⅱ) and As(Ⅲ)contamination.

Extraordinary toughening enhancement in nonstoichiometric vanadium carbide

1.Introduction Fracture toughness is the ability of materials against both the initiation and propagation of cracks[1],which is a crucial mechanical property for safety-critical applications of structural materials.Although the yield strength of ceramics is significantly higher than that of metallic materials,the fracture toughness is severely lower than that of metallic materials due to the strongly directional covalent bonding[1-3].For a long time,how to improve the fracture toughness of ceramics without the deterioration of strength(or hardness)has been one of the most challenging problems in materials science.