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The identification of synthetic antioxidants has considerable significance in food safety. Here, we described the development of a colorimetric sensor array for rapid detection of eight antioxidants in food through the redox reaction between CoOOH and antioxidants in the presence of colorimetric signal indicators. The CoOOH nanoflakes exhibited high catalytic oxidation activity and can independently catalyze oxidation signal indicators showing different colors. The color reaction was inhibited to different degrees in the presence of antioxidants, which resulted in distinct signal response patterns for their discrimination. The method showed good linearity in the range from 50 to 1000 nM for butylated hydroxytoluene (BHT), butylhydroxyanisole (BHA), propyl gallate (PG) and

Norfloxacin (NOX), a kind of quinolone antibiotic, is widely used in disease treatment and the control of human and livestock products. Due to overuse, norfloxacin has become a common organic pollutant in water. We combine the high specific surface area and high stability of metal-organic frameworks with the high selectivity of molecularly imprinted polymers. By grafting a carbon-carbon double bond on the surface of UiO-66-NH

Trivalent praseodymium (Pr3+)-doped materials have been extensively used in high-resolution laser spectroscopy, owing to their outstanding conversion efficiencies of plentiful transitions in the visible laser region. However, to clarify the microstructure and energy transfer mechanism of Pr3+-doped host crystals is a challenging topic. In this work, the stable structures of Pr3+-doped yttrium orthoaluminate (YAlO3) have been widely searched based on the CALYPSO method. A novel monoclinic structure with the Pm group symmetry is successfully identified. The Pr3+ impurity can precisely occupy the Y3+ position and get incorporated into the YAlO3 (YAP) host crystal with a Pr3+ concentration of 6.25%. The result of the electronic band structure reveals a 3.62 eV band gap, which suggests a semiconductor character of YAP:Pr. Using our developed well-established parametrization matrix diagonalization (WEPMD) method, we have systematically analyzed the energy level scheme and proposed a set of newly improved parameters. Additionally, the energy transfer mechanism of YAP:Pr is clarified by deciphering the numerical electric dipole and magnetic dipole transitions. The popular red emission at 653 nm is assigned to the transition 3P0 → 3F2, while the transition 3P0 → 3H4 with a large branching ratio is predicted to be a good laser channel. Many promising emission lines for laser actions are also obtained in the visible light region. Our results not only provide important insights into the energy transfer mechanisms of rare-earth ion-doped materials but also pave the way for the implementation of new types of laser devices.

Superhalogens, predicted 40 years ago, have attracted considerable attention due to their potential as building blocks of novel materials with various applications. While a large number of superhalogen clusters have been theoretically predicted and experimentally synthesized, they either require the use of a metal cation or electron counting rules. In particular, very rare endohedral cage clusters in defiance of the above requirements have been found to be superhalogens. In this work, motivated by recent experimental advances in endohedral cage clusters, we present a rational design principle for creating a new class of such superhalogens. Focusing on the chemical formula of A@Si

Trivalent rare-earth holmium ion (Ho3+) doped yttrium oxide (Y2O3) has attracted great research interest owing to its unique optoelectronic properties and excellent performances in many new-type laser devices. But the crystal structures of the Ho3+-doped Y2O3 system (Y2O3 : Ho) are still unclear. Here, we have carried out a first-principle study on the structural evolution of the trivalent Ho3+ doped Y2O3 by using the CALYPSO structure search method. The results indicate that the lowest-energy structure of Ho3+-doped Y2O3 possesses a standardized monoclinic P2 phase. It is found that the doped Ho3+ ion are likely to occupy the sites of Y3+ in the host crystal lattice, forming the [HoO6]9− local structure with C2 site symmetry. Electronic structure calculations reveal that the band gap value of Ho3+-doped Y2O3 is approximately 4.27 eV, suggesting the insulating character of Y2O3 : Ho system. These findings could provide fundamental insights to understand the atomic interactions in crystals as well as the information of electronic properties for other rare-earth-doped materials.

Three-, four-, and sixfold excitations have significantly extended the subjects of condensed-matter physics. There is an urgent need for a realistic material that can have coexisting three-, four-, and sixfold excitations. However, these materials are uncommon because these excitations in electronic systems are usually broken by spin-orbit coupling (SOC) and are normally far from the Fermi level. Unlike the case in electronic systems, phonon systems with a negligible SOC effect, not constrained by the Pauli exclusion principle, provide a feasible platform to realize these excitations in a wide frequency range. Hence, in this work, we demonstrate by first-principles calculations and symmetry analysis that perfect three-, four-, sixfold excitations appear in the phonon dispersion rather than the band structures of ${\mathrm{Zr}}_{3}{\mathrm{Ni}}_{3}{\mathrm{Sb}}_{4}$, which is a well-known indirect-gap semiconductor with an ${\mathrm{Y}}_{3}{\mathrm{Au}}_{3}{\mathrm{Sb}}_{4}$-type structure. This material features a threefold-degenerate quadratic contact triple-point phonon, fourfold-degenerate Dirac point phonon, and sixfold degenerate point phonon. Moreover, these nodal point phonons are very robust to uniform strain. Two obvious phonon surface arcs of the (001) plane are extended in the whole Brillouin zone, which will facilitate their detection in future experimental studies. The current work provides an ideal model to investigate rich excitations in a single material.

We have calculated and discussed the electronic and optical properties of two-dimensional (2D) CdS/g-C6N6 heterostructures by using hybrid density functional of HSE06. The CdS and g-C6N6 can form CdS/g-C6N6 heterostructures through weak van der Waals (vdW) interactions. The CdS/g-C6N6 composites are indirect bandgap semiconductors and type-II heterostructures. The visible light absorbtion of CdS/g-C6N6 composites is obviously improved, and the band alignment is beneficial for spontaneous water redox reactions. Furthermore, the electrons migrating from CdS layer to g-C6N6 leads to the built-in electric field formation, which promotes the effective separation of photogenerated carriers. These factors imply CdS/g-C6N6 composites are promising visible light water-splitting photocatalysts.

There has been considerable research interest paid to rare-earth transition-metal-doped Y3Al5O12, which has great potential for application as a laser crystal of new-type laser devices because of i...

Trivalent praseodymium (Pr

Two-dimensional (2D) magnetic materials with strong magnetism, long magnetic relaxation times, high temperature ferromagnetism, and large magnetic anisotropy energy (MAE) are promising for applications of nanoscale spintronic devices. Using the spin-orbital coupling density functional theory (DFT) calculations, we investigate the structural stability, electronic structures, and magnetic properties of graphenelike carbon-nitride ($\mathrm{gh}\text{\ensuremath{-}}{\mathrm{C}}_{3}{\mathrm{N}}_{4}$) sheets with the adsorption of whole series of $4f$-block elemental (lanthanide; Ln) atoms. Our results demonstrate that Ln atoms can be stably embedded into/above the center of the cavity of $\mathrm{gh}\text{\ensuremath{-}}{\mathrm{C}}_{3}{\mathrm{N}}_{4}$ monolayer and significantly affect the electronic and magnetic properties. Upon single Ln atom adsorption, all Ln@$\mathrm{gh}\text{\ensuremath{-}}{\mathrm{C}}_{3}{\mathrm{N}}_{4}$ systems show metal character, large spin and orbital magnetic moments, and most of them favor the long-range ferromagnetic ordering. Interestingly, Pr, Nd, Ho adsorbates would possess total magnetic moments of 1.09, 1.47, 6.13 ${\ensuremath{\mu}}_{B}$, high Curie temperatures (${T}_{c}$) of 593, 699, 700 K, large MAEs of 4.89, $\ensuremath{-}17.88$, 21.31 meV/Ln atom, respectively. Based on the electronic structure analyses, we propose that the $4f$ electron hopping between the occupied and unoccupied states around the Fermi level contributes to the large MAE, significant intratomic Ln-$sd$ orbital hybridization with N-$2p$ orbital hybridization gives rise to structural stability, and the coexistence of superexchange and RKKY interactions determines the long-term ferromagnetic coupling between Ln atoms. The present study demonstrates that Ln@$\mathrm{gh}\text{\ensuremath{-}}{\mathrm{C}}_{3}{\mathrm{N}}_{4}$ sheets have significant promise for applications in spintronics such as high density memory devices or for magnetic random access memory.

Taste and odor (TO) compounds are important water pollutant, some of which are toxic. The relevant studies are all expand upon the well-known TO compounds but for the unknown odors in smelling water. In this work, a method combining purge and trap with gas chromatograph-mass spectrometer (PT-GC/MS) and disperse solid-phase extraction with gas chromatograph (GC) was first proposed to detect TO compounds in unknown odorous water accurately. Firstly, PT-GC/MS was used for a qualitative test on unknown odors in smelling water and determine the analytes. The hollow CoNi-layered double hydroxide (LDH) on graphene oxide (GO) was then used as a composite adsorbent to pretreat the water, in which the GO provided large specific surface, and the LDH worked as a confinement cavity to enhance capture and retention capacity for volatile organic compounds (VOCs). According to the properties of TO compounds determined by PT-GC/MS in water, a corresponding GC method was established for accurately quantitative analysis. In this paper, five TO compounds were detected simultaneously, including dimethyl sulfide, meistylene, N, N-dimethylbenzylamine, 2, 4-dimethylbenzaldehyde and 2, 4-di-tert-butylphenol. Extraction parameters were optimized, including ratio of desorption solvent, amount of adsorbent, pH value, etc. Under the optimal conditions, the detection limits for analysis were 1.14 μg/L to 3.07 mg/L. The satisfactory recoveries were 94-98%. Furthermore, two optimal determination outcomes of odor waters from different places support the practicability of the method, which is expected to be widely used in the detection of unknown odors in smelling water.

Trivalent rare-earth holmium ion (Ho

Thulium-doped yttrium aluminum garnet (Tm:YAG) is an important solid-state laser crystal. The energy-level splitting within it is still an unresolved problem. Here, we perform a theoretical study on the microstructure of Tm3+-doped YAG using the CALYPSO structure search method in conjunction with first-principles calculations. The calculated results show that the 4.16% doping concentration of Tm3+ impurity causes an obvious structural distortion of YAG crystal, forming an orthorhombic phase in C222 symmetry. On the basis of our developed WEPMD method, we obtain a new and complete set of free-ion and crystal field parameters by a good fit (with proper irreducible representations) to 69 observed energy levels and determine the exact energy-level splitting of Tm3+ in YAG. The calculated Stark levels and electric dipole transitions are in excellent agreement with the measured data and similar theoretical calculations. Some promising emission lines between 3F3, 3F2, 1D2, and 1I6 states are presented. These fin...

Using a three-dimensional classical ensemble method, we present a theoretical study of nonsequential double ionization of ArXe dimer aligned along the minor axis of the elliptically polarized laser pulse. Numerical results show that NSDI probability firstly increases and then decreases with the laser ellipticity increasing, which is different from atoms. Moreover, the correlated electron momentum spectra from elliptical polarization are always asymmetric, and the asymmetry is enhanced as the ellipticity increases. Analysis backward in time indicates that in NSDI of ArXe aligned along the minor axis the recollision occurs via a semi-elliptical trajectory.

The Ce 3 + -doped YAG crystal has drawn considerable interest because of its important application in the white light-emitting diodes. However, the fundamental understanding of its microstructure is still lacking. In this work, the structural evolution and electronic properties of Ce 3 + -doped YAG crystal are systematically studied on the basis of the density functional theory (DFT) as well as Crystal structure Analysis by Particle Swarm Optimization (CALYPSO) method. A novel stable phase with cage-like structure and C 222 space group of Ce 3 + -doped YAG crystal has been reported. The calculations of the electronic band structure indicate that the Ce 3 + -doped YAG possesses a conductive character because the Fermi level is crossed through by the conduction band. By analyzing the electronic density of states (DOS), we conclude that the reason of the elimination of the insulated character can be attributed to the impurity Ce 3 + . The bond character between the Ce-O and Y-O are identified by the calculation of the electron localization function (ELF). These results can offer significant information for exploring new rare-earth doped laser materials and also provide useful insights to elucidate some experimental phenomena.

Halogen-free electrolytes are important for the development of the next-generation rechargeable Li-ion batteries. Due to its ultrahigh oxidative stability and weak binding with Li+, the bison anion B(CN)4– has recently been found to be a potential candidate for such electrolytes. Unfortunately, Li-bison salt has very poor solubility in ionic liquids, leading to the possible formation of large aggregates, thus hindering its potential for commercial application. Here, by replacing the cyanide with much less toxic thiocyanide, we propose a new weakly coordinating anion, B(SCN)4–, which does not suffer from this drawback. We show that this new member of the tetracyanoborate family is unlikely to form aggregated complexes with Li+ and would be a good candidate to be used in electrolytes.

Using first-principles calculations, the hydrogen storage capacity of bimetal alloy nanostructures has been carried out. We select two stable structures, Al 10 Li 8 and Al 13 Li 20 , as paradigms, where Li atoms are exposed and unsaturated on the surfaces of Al clusters. The advantages of these structures are: (1) Li atoms do not cluster on the surfaces of Al nanoclusters. (2) Al 10 and Al 13 are much lighter than previous studied systems C 60 and C 48 B 12 . (3) Both Al 10 Li 8 and Al 13 are very stable magic clusters. We show that in these two systems each exposed Li atom is able to bind one H 2 molecule. The average binding energies are 0.10 and 0.13 eV/H 2 , with gravimetric densities of 4.1 wt% and 7.5 wt%, respectively, nearly meet and exceed the requirement of 5.5 wt% set by DOE.

Using first-principles calculations, we have explored the magnetic properties of zigzag edge graphene nanoribbons (ZGNR) with planar tetrahedral coordinated carbon (ptC) or silicon (ptSi). It is observed that the ptC can convert antiferromagnetic-coupled ZGNR into ferromagnetic one, while the ptSi cannot. These contrast results can attribute to the differences between magnetic ptC and non-magnetic ptSi atoms. Moreover, both ZGNR-ptC and ZGNR-ptSi structures are metallic and stable. Thus, the unique magnetic properties and high stabilities of these systems strongly suggest the feasibility of designing novel ferromagnetic devices.

Stabilizing small multiply charged negative ions in the gas phase has been of considerable interest in recent years. B12H122− is one of the most well-known dianions which is stable against auto-detachment of its second electron in the gas phase by 0.9 eV, whereas BnHn2− with n < 12 is unstable. Using density functional theory, we have examined systematically the role of ligands in stabilizing smaller mono- and di-anions of BnXn and CBn−1Xn (n = 5–10; X = H, F, CN). We show that the stability of the negative ions of these complexes increases with the electron affinity of the ligand and Bn(CN)n2− can even be stable against electron emission for n ≥ 5. We also show that CBn−1(CN)n2− is stable against electron emission for n ≥ 8, even though these moieties contain one electron more than needed to satisfy the Wade–Mingos rule. We have examined the potential of these stable negative ions as building blocks of electrolytes in Li-ion batteries. By calculating the binding energies between the CBn−1Xn1−,2− and Li+, we find that some of these clusters may even outperform CB11H12− as electrolytes in metal-ion batteries.

Photocatalytic water-splitting for hydrogen generation is a promising way to solve the energy crisis, yet the design of efficient photocatalysts is still a challenge. By utilization of first principles calculations, we predict the photocatalytic properties of monolayer boron phosphide (BP) based BP/XY

Nonsequential double ionization (NSDI) of Ar in co-rotating two-color circularly polarized (TCCP) laser fields is investigated with a three-dimensional classical ensemble model. Our numerical results indicate that co-rotating TCCP fields can induce NSDI by recollision process, while the yield is an order of magnitude lower than counter-rotating case. NSDI yield in co-rotating TCCP fields strongly depends on field ratio of the two colors and achieves its maximum at a ratio of 2.4. In co-rotating TCCP fields, the short recollision trajectory with traveling time smaller than one cycle is dominant. Moreover, the recollision time in co-rotating TCCP laser fields depends on the field ratio, which is mapped to the electron momentum distribution. This provides anavenue to obtain information about recollision time and access the subcycle dynamics of the recollision process.

There has been considerable research interest paid to rare-earth transition-metal-doped Y

Rare-earth Erbium-doped yttrium aluminum garnet (Er: YAG) shows great research interests in many kinds of solid-state lasers. However, the crystal structures of Er: YAG are unclear. Herein, we conduct a systematic exploration of the microstructure of Er-doped YAG crystal by using the CALPSO method with first-principle calculations. A novel structure with the Er3+ impurity concentration of 4.16% is identified, which belongs to C222 space group. It is found that the impurity Er3+ ion substitutes the central site of Y3+ ion in the host crystal lattice. This work could provide important information for understanding the rare-earth doped laser materials.

Relative phase effect of nonsequential double ionization (NSDI) of aligned molecules by counter-rotating two-color circularly polarized (TCCP) fields is investigated with a three-dimensional classical ensemble model. Numerical results show that NSDI yield in counter-rotating TCCP fields sensitively depends on the relative phase of the two components, which exhibits a sin-like behavior with the period of π/2. NSDI yield achieves its maximum at the relative phase π/8 and minimum at 3π/8. Back analysis indicates the recollision time and the return angle of the electron strongly depend on the relative phase of the two components, which results in the dominant emission direction of the electrons, is different for different relative phases. This indicates that the recollision process can be steered by changing the relative phase of the two components in counter-rotating TCCP laser fields. Meantime, it provides an avenue to obtain information about the recollision time and the return angle in the recollision process from the electron momentum distribution.

Thulium-doped yttrium aluminum garnet (Tm:YAG) is an important solid-state laser crystal. The energy-level splitting within it is still an unresolved problem. Here, we perform a theoretical study on the microstructure of Tm

In this work, graphene-like ZnO (g-ZnO)-based two-dimensional (2D) heterostructures (ZnO/WS₂ and ZnO/WSe₂) were designed as water-splitting photocatalysts based on the hybrid density functional. The dependence of photocatalytic properties on the rotation angles and biaxial strains were investigated. The bandgaps of ZnO/WS₂ and ZnO/WSe₂ are not obviously affected by rotation angles but by strains. The ZnO/WS₂ heterostructures with appropriate rotation angles and strains are promising visible water-splitting photocatalysts due to their appropriate bandgap for visible absorption, proper band edge alignment, and effective separation of carriers, while the water oxygen process of the ZnO/WSe₂ heterostructures is limited by their band edge positions. The findings pave the way to efficient g-ZnO-based 2D visible water-splitting materials.

authoren Structural, electronic, elastic, and thermodynamic properties of the spin-gapless semiconducting (SGS) Mn2CoAl inverse Heusler alloy under pressure are investigated by using the density functional theory (DFT) and the quasi-harmonic Debye model. The calculated equilibrium lattice parameter and SGS behavior agree with the experimental and other theoretical data. It is only when the external pressure is beyond about 25 GPa that the SGS behavior and dynamical stability are destroyed, indicating that the SGS behavior is robust against pressure less than 25 GPa in everyday experiments. Furthermore, the thermal properties, including bulk modulus B, thermal expansivity , Gruneisen parameter , heat capacity C, and Debye temperature of Mn2CoAl are evaluated up to 25 GPa. These thermodynamic properties will be referenced in the further experiments. The calculated phonon dispersion curves of Mn2CoAl at different pressures.

Recollision dynamics and electron correlation behavior are investigated for several long laser wavelengths (1200-3000 nm) in nonsequential double ionization (NSDI) of helium using three-dimensional classical ensembles. Numerical results show that for these long wavelengths NSDI events are mainly from the multiple-return trajectory which is different from the case of 800 nm. Moreover, with increasing laser wavelength NSDI events move from the diagonal to the two axes in the correlated electron momentum distributions, and finally form an experimentally observed prominent V-shaped structure [Phys. Rev. X 5, 021034 (2015)] in the first and third quadrants. Back analysis indicates that the asymmetric energy sharing between the two electrons at recollision is responsible for the formation of the prominent V-shaped structure of 3000 nm.

Photocatalytic water-splitting for hydrogen generation is a promising way to solve the energy crisis, yet the design of efficient photocatalysts is still a challenge. By utilization of first principles calculations, we predict the photocatalytic properties of monolayer boron phosphide (BP) based BP/XY2 (X = Mo, W; Y = S, Se) composites of different rotated configurations. Our results suggest that the BP/XY2 composites can be stably formed, and the narrowed bandgaps ensure these composites are suitable for absorbing visible light. The bandgaps and band edge positions are slightly affected by the rotation angles. The BP/MoS2, BP/MoSe2, and BP/WSe2 are type II heterostructures. Furthermore, the transferred charge from BP to XY2 layers leads to the formation of electric fields, which efficiently separate the photoinduced carriers. The band alignments of BP/MoS2, BP/MoS2, BP/MoSe2, and BP/WSe2 satisfy the requirements of overall water-splitting within the pH scope of 3.6-7.9, 6.8-7.9, 4.0-8.0, and 8.7-8.8. This work will provide valuable insight for designing efficient water-splitting photocatalysts.

The structural, electronic, and optical properties of two-dimensional (2D) CdO/g-C6N6 nanocomposite are studied through hybrid density functional. The results show that the CdO monolayer can contact with g-C6N6 through van der Waals interaction to form the CdO/g-C6N6 heterostructure. A narrower bandgap value is found for CdO/g-C6N6, compared to both CdO monolayer and g-C6N6 monolayer, which is conductive to the absorption of visible-light. Furthermore, the CdO/g-C6N6 composite shows appropriate band alignment and efficient charge separation. These factors indicate that the CdO/g-C6N6 composite is a promising visible-light water-splitting photocatalyst.

Nonsequential double ionization of helium in counter-rotating two-color circularly polarized laser fields is investigated with a three-dimensional classical ensemble model. At moderate intensity, the momentum distribution of the two electrons shows a maximum in the middle of each side of the triangle of the negative vector potential. At high intensity, the momentum distribution exhibits a double-triangle structure, which is attributed to the different values of the laser intensity where the two electrons are released after recollision. At low intensity, the momentum distribution shows a shift deviating from the middle of the side of the triangle of the negative vector potential. This is because the first electrons are emitted within a narrow time window after the field maximum. In addition, at low intensity, double-recollision events and NSDI originating from doubly excited states induced by recollision are prevalent.

Hybrid density functional has been adopted to theoretically investigate the structural, electronic, and optical properties of AlN/MoSe2, AlN/WS2, and AlN/WSe2 heterostructures with the consideration of effects of strains and pH so as to explore their potential visible light photocatalytic activities for water splitting. AlN/MoSe2, AlN/WS2, and AlN/WSe2 heterostructures with proper strains are energetically favorable due to the good lattice mismatch and the interface adhesion energies between the constituent monolayers. The charge accumulation/depletion around the interfaces of these heterostructures are beneficial for the generation and separation of photogenerated carriers, which is also favorable for improving the photocatalytic activities. Through adjusting the strains and the pH of the electrolyte, the AlN/MoSe2, AlN/WS2, and AlN/WSe2 heterostructures could own suitable bandgaps for absorbing visible light and appropriate band edge positions with respect to water redox levels for the spontaneous generation of hydrogen and oxygen. The band edge positions of AlN/MoSe2, AlN/WS2, and AlN/WSe2 heterostructures are thermodynamically feasible for over water splitting when the pHs of the electrolyte are respectively around 13, in the range of 4.5–8.1, and greater than 10.7. These findings pave a way to design the efficient AlN-based heterostructures for visible light photocatalytic water splitting.

An investigation on many-body effects of solid argon at high pressure was conducted based on a many-body expansion of interaction energy. The three- and four-body terms in the expansion were calculated using the coupled-cluster method with single, double, and noniterative triple theory and incremental method, in which the configurations of argon trimers and tetramers were chosen as the same as those in the actual lattice. The four-body interactions in compressed solid argon were estimated for the first time, and the three-body interaction ab initio calculations were extended to a small distance. It shows that the four-body contribution is repulsive at high densities and effectively cancels the three-body lattice energy. The dimer potential plus three-body interaction can well reproduce the measurements of equation of state at pressure approximately lower than ∼60 GPa, when including the four-body effects extends the agreement up to the maximum experimental pressure of 114 GPa.

First-principles investigations are employed to provide a fundamental understanding of the structural features, phase stability, mechanical properties, Debye temperature, and hardness of manganese tetraboride. Eight candidate structures of known transition-metal tetraborides are chosen to probe. The calculated lattice parameters, elastic properties, Poisson’s ratio, and [Formula: see text] ratio are derived. It is observed that the monoclinic structure with [Formula: see text] symmetry (MnB4–MnB4) is the most stable in energy. The mechanical and thermodynamic stabilities of seven possible phases are confirmed by the calculated elastic constants and formation enthalpy. Moreover, the analysis on density of states demonstrates semiconducting behavior of MnB4–MnB4 and different metallic behaviors of other phases. The estimated hardness of MnB4–MnB4 is 38.3 GPa, which is in good agreement with experimental value. Furthermore, the relationship between hardness and Debye temperature is investigated and verifies that MnB4–MnB4 is a newly potential semiconducting ultrahard material with high melting point. It provides a new perspective of searching for semiconducting superhard materials to be applied in extreme conditions.

Using the first-principles calculations, we provide a systemic understanding of the structural features and phase stability, mechanical and electronic properties, as well as the roles of boron (B) atom arrangement in the hardness for chromium borides. The structural and relative energy searches together with formation enthalpy confirm the most stable Cr2B with an orthorhombic Fddd symmetry, CrB with an orthorhombic Cmcm symmetry, CrB2 with a hexagonal P63/mmc symmetry and chromium tetraboride (CrB4) with an orthorhombic Pnnm symmetry. The shear modulus, Young’s modulus and [Formula: see text] increase with the boron content, while the Poisson’s ratio and [Formula: see text] ratio have an opposite tendency. Moreover, due to higher B content, strong three-dimensional (3D) covalent B networks and lower metallic contribution, CrB4 with Pnnm symmetry has the largest hardness value (46.8 GPa), exceeding the superhard limit, indicating its superhard nature.

First-principles calculations based on density functional theory (DFT) and quasi-harmonic Debye model are performed to study the structural, elastic, electronic and thermodynamic properties of the Co 2 YZ (Y=Sc, Cr and Z=Al, Ga) Heusler alloys. It is found that the spin polarization of Co 2 CrZ at Fermi level raises considerably, and Co 2 ScZ keeps the non-magnetic feature when the external pressure increases. Although outstanding performance of half-metallicity appears to Co 2 CrZ, the dynamical stability order exhibits that Co 2 ScZ > Co 2 CrZ as the result of phonon dispersion analysis. The influence of external pressure and temperature on the volume compression ratio, bulk modulus, heat capacity and thermal expansion coefficient are took fully into account and the outcomes from calculation obey the corresponding thermomechanics laws in the quasi-harmonic Debye model.

In this study, finite element analysis (FEA) has been used to investigate the effects of different Laval nozzle throat sizes on supersonic molecular beam. The simulations indicate the Mach numbers of the molecular stream peak at different positions along the center axis of the beam, which correspond to local minimums of the molecular densities. With the increase of the throat diameter, the first peak of the Mach number increases first and then decreases, while that of the molecular number density increases gradually. Moreover, both first peaks shift progressively away from the throat. At the last part, we discuss the possible applications of our FEA approach to solve some crucial problems met in modern transportations.