Solid State Communications最新文献

Two-dimensional (2D) Janus materials have received considerable interest because of their robust piezoelectricity generated by breaking the central symmetry, which have potential applications in micro/nanomotor and flexible robot skins. However, in the previous 2D piezoelectric material research system, strain and electric polarization were limited to the base plane, greatly restricting its applications. Based on density functional theory (DFT), we have found the monolayer and multilayer Janus GaXI (X = S, Se, or Te) with high planar and vertical piezoelectricity. The maximum out-of-plane piezoelectric coefficient (d₃₃ = 19.96 p.m./V) of these materials is 7.8 and 2.6 times larger than those of the conventional three-dimensional (3D) piezoelectric materials α-quartz and AIN, respectively. The monolayer Janus GaTeI exhibits the largest in-plane piezoelectric coefficient (d₁₁ = 11.27 p.m./V). Additionally, it is worth noting that the multilayer Janus GaXI of six high-symmetry stacking sequences exhibits stronger out-of-plane piezoelectric polarization in the vertical direction than the monolayer. The structure of GaSI monolayer is similar to that of honeycomb graphene monolayer, and GaSI multilayer is also similar to graphene multilayer. In the Janus GaXI system, the sign of the electrostatic potential gradients, the direction of out-of-plane polarization and the sign of relaxed-ion d31 values are the same. Our study shows that monolayers and multilayer Janus GaXI have excellent piezoelectricity, and they have wildly potential applications in micro/nano-electronic devices.

The major goal of the research described in this paper is to investigate the structure of electronic band and band gap of the novel semiconductor lead (II) trioxovanadate (V) chloride (PbVO₃Cl). Depending on both experimental and theoretical (computational) results, the utility of PbVO₃Cl as a semiconductor in solar fuel devices was discussed. The optical band gap was determined experimentally by applying Tauc Plot method to the absorption spectra of PbVO₃Cl. Additionally, computational approaches for the structure prediction of PbVO₃Cl have been studied. The electronic band structures were examined theoretically using local density (LDA), generalized gradient (GGA), and hybrid (HSE06) approximations. PbVO₃Cl, which has an optical band gap of about 2.2 eV, has been shown to have promising photocatalytic properties. As a result of these approximations, the transition type of PbVO₃Cl was determined as indirect. We also discussed the potential future application of PbVO₃Cl in Lewis solar fuel devices as a combination of the photoanode and Si photocathode. And the solar efficiency of the PbVO₃Cl–Si double-layer semiconductor system was calculated. Further experimental proofs can be important.

Although ZrAl₂ has been extensively studied, its structural features and properties under high pressures remain unclear. Using the CALYPSO structural search method combined with first-principles calculations, we investigated the structural evolution and mechanical stability of ZrAl₂ at high pressures. Our research reveals that at 198 GPa, ZrAl₂ undergoes a phase transition from the P6₃/mmc phase to the Pmmm phase. This transition results in a volume collapse of 2.1%, indicating a first-order phase change. A comprehensive analysis of the elastic constants and phonon spectra confirms the structural stability of four new phases of ZrAl₂. Our research findings provide a comprehensive view of the structural evolution of ZrAl₂ under high pressure. This valuable information enhances the understanding of the physical and chemical properties of C14-type ZrAl₂ when subjected to high-pressure conditions.

The aim of this study is to investigate how different pressure levels and annealing times affect the local atomic structure and mechanical properties of pure zirconium metallic glasses. Using molecular dynamics simulations with the embedded atom method, we explored how these changes influence the material's inherent characteristics. Analysis of the radial distribution function, coordination number, and Voronoi tessellation revealed a spectrum of structural arrangements in metallic glass formed across a pressure range of 0–70 GPa. Additionally, the glass transition temperature increased with increasing pressure, accompanied by reduced free volume. The annealing process, ranging from 0 to 5 ns on metallic glass synthesized under 0 GPa pressure, showed the coordination number's significance in achieving a glassy state. Regarding mechanical behavior, both elastic constants and moduli showed a progressive increase with rising pressure, while Young's modulus and hardness displayed enhanced values with longer annealing times.

In this work, all-d metal Heusler alloys Ni–Mn–Cr were predicted by first principles. Their structure, magnetism, tetragonal distortion and electronic properties were studied. The cubic groud state structures of Ni₂MnCr and NiMnCr₂ are XA type, and that of NiMn₂Cr is L2₁ type. All of them have magnetism. The change of their lattice constants is closely related to the covalent radius of atoms. Ni₂MnCr has a stable tetragonal phase and may undergo martensitic transition. NiMn₂Cr has a lower energy tetragonal phase, but is dynamically unstable. The equilibrium volumes of the two compounds expand through tetragonal distortion. NiMnCr₂ does not have a lower energy tetragonal phase. In the tetragonal distortion, the atomic magnetic moments are influnced by the interatomic distance and the magnetic moments of neighboring atoms. The origin of the tetragonal distortion and magnetic properties was discussed in terms of the electronic density of states.

The room temperature compressive creep behavior is a key issue for the titanium alloys welded structural components served in deep-sea environment. In the present work, the compressive creep behavior of different areas for TC4 titanium alloy joints with vacuum electron beam welding was systematically studied, and it is found that the fusion zone (FZ) of TC4 titanium alloy joints has the minimum creep strain rate. This is mainly because the creep deformation of TC4 titanium alloy is mainly controlled by the movement of dislocations in the α or α′ phases, the size of α′ phase in FZ is small, and thus the dislocation slip is limited. MD simulation results have further revealed that the room temperature compressive creep nature of α-Ti can be regarded as a dynamic hysteresis phenomenon in plastic strain and is dominated by the dislocation movement.

In the present work, we report the synthesis of Pb–Bi alloy with enhanced T_c of up to 9K, which is higher than that of Pb. The alloy is synthesized via a solid-state reaction route in the vacuum-encapsulated quartz tube at 700°C in an automated furnace. The synthesized sample is characterized by X-ray Diffraction(XRD) and Energy dispersive X-ray analysis(EDAX) for its phase purity and elemental composition. Rietveld refinement of XRD reveals that the end product is a majority hexagonal Pb₇Bi₃, with minor rhombohedral Bi. The electronic transport measurement shows metallic behavior with the Debye temperature of 108K and a superconductivity transition temperature (T_c) below 9K, which is the maximum to date for any reported Pb–Bi alloy, Pb or Bi at ambient pressure. Partial substitution of Bi at the Pb site may modify the free density of electronic states within the BCS model to attain the optimum T_c, which is higher by around 2K from the reported T_c of Pb. The superconductor phase diagram derived from magneto-transport measurements reveals that the synthesized alloy is a conventional superconductor with an upper critical field (H_c2) of 3.9 T, which lies well within the Pauli paramagnetic limit. The magnetization measurements carried out following ZFC(Zero Field Cool) protocols infer that the synthesized alloy is a bulk superconductor below 9K. The isothermal M-H(Magnetization vs. Field) measurements performed below T_c establish it as a type-II superconductor. The specific heat capacity measurements show that the Pb–Bi alloy is a strongly coupled bulk superconductor below around 9K with possibly two superconducting gaps.

The study on the zintl compounds CaMg₂Pn₂ (Pn = P, As), compounds utilizing density functional theory (DFT) through the WIEN2k code comprehensively examines its structural, electronic, optical, and thermoelectric properties. Generalized gradient approximation (GGA) and modified Becke-Johnson (mBJ) potentials are used to determine the exchange-correlation potential. The electronic analysis of the CaMg₂Pn₂ compounds, reveals that this material behaves as a semiconductor, possessing an indirect band gap of 1.87 eV and 1.76 eV. The study of the optical properties of CaMg₂Pn₂, including its refractive index, extinction coefficient, electron energy loss, dielectric tensor, and optical conductivity, alongside the specific finding that it does not absorb energy below 2.60 eV, provides valuable insights. In addition, BoltzTrap is a software used to calculate the transport properties against temperature (200–1200K) and chemical potential of materials based on their electronic structures. The highest power-factor (PF) 5.57 × 10¹¹ W/K²ms, 5.0 × 10¹¹ W/K²ms at 300 K was attained for CaMg₂Pn₂ (Pn = P, As) compounds. These findings suggest that CaMg₂Pn₂ has potential as a thermoelectric material with interesting characteristics. Because of their exceptional optoelectronic as well as high PF values, this group of materials holds significant promise for applications in optoelectronic and thermal devices. Their properties suggest potential advancements in fields such as solar energy, light emission technologies, and efficient thermal management systems.

In the present work, the density functional theory has been utilised in inspecting the ground state-structural, electronic, magnetic, optical, elastic and thermodynamic properties of new semiconductor RbTaX (X = P and As) half-Heuslers. Out of the possible three structures (α, β, γ) studied in ferromagnetic (FM) as well as non-magnetic (NM) phases, α – FM phase is found to be the most stable configuration. Both studied materials have estimated a net magnetic moment of 3μ_B, following the Slater-Pauling rule ($M_{tot}=Z_{tot}-8$). With the use of modified Becke Johnson potential (mBJ) potential, the band profile reveals non-zero band gap in the spins and henceforth display spin filter property in the compounds. The predicted energy band gaps for RbTaP and RbTaAs are 3.04 and 2.87 eV for minority spin channels and 0.137 and 0.26 eV for majority spin channels, respectively. This unique feature of the Heusler compound may be advantageous for quantum information processing and spin-transport in electronic and magnetic devices. Also, a moderate exchange splitting and a Curie temperature well above the room temperature are noted. The stability of the materials under investigation was further confirmed by calculations of cohesive energy, formation energy, and second order elastic constants. The optoelectronic as well as thermodynamic properties of the studied compounds are also investigated. The estimated high value of refractive index (>4) is making them suitable for optical lenses. Moreover, photon energy absorption in the visible and ultraviolet spectrums renders them valuable for UV-VIS absorbers.

The current research study investigated the impact of lacunar manganite on the magnetocaloric effect and explored the correlation between the electrical and magnetic properties of the La_0·8Na_0.1□_0.1MnO₃ compound. Structural analysis confirmed the presence of a predominant phase and a minor Mn₃O₄ phase. The observed hysteresis loop indicates the exchange bias effect, suggesting the material's suitability for spintronic and magnetic read-write head devices. The magnetocaloric properties of the polycrystalline manganites La_0·8Na_0.1□_0.1MnO₃ were examined through resistivity and magnetic measurements. The sample exhibits a negative maximum magnetic entropy change ΔS of 5.56 J/kg.K around its Curie temperature (T_C = 295K) at a magnetic field of 5T. The magnetocaloric effect value was estimated using a phenomenological model based on magnetization calculations as a function of temperature under different magnetic fields M (T, H). The magnetic entropy ΔS_M was determined using Landau's phase transition theory. The relationship between magnetic order and transport behavior, expressed through the resistivity and magnetization relationship near T_C, was consistent with Maxwell–Weiss relation results. The findings indicate that the studied sample is an excellent candidate for multifunctional spintronic devices, magnetic read-write head devices, and magnetic refrigeration.