- 标题
- 摘要
- 关键词
- 实验方案
- 产品
-
First-principles study of the ordered structures of the single crystal PMN(0.75)-PT(0.25) and their ferroelectric characteristics
摘要： For the various PMN(0.75)-PT(0.25) ordered structures, first principles density functional studies using local density approximation (LDA) framework and augmented projected augmented wave (PAW) pseudopotentials. All possible 20-atom ordering along the [001]-, [011]- and [111]- directions are considered in the ab-initio code VASP. Also, we conducted linear response with density functional perturbation theory (DFPT) which is implemented in the VASP to compute the electronic dielectric tensors and piezoelectric tensors. The polar response is strongly dependent of the ionic ordering. Some PMN(0.75)-PT(0.25) ordered structures show strong piezoelectric characteristics.
关键词： first-principles calculation,piezoelectric characteristics,Pb(Mg1/3Nb2/3)O3-PbTiO3,ordered structure
更新于2025-09-10 09:29:36
-
First Experimental Demonstration and Mechanism of Abnormal Palladium Diffusion Induced by Excess Interstitial Ge
摘要： This letter represents the ?rst direct experimental demonstrations and mechanism proposal regarding abnormal palladium diffusion into germanium (Ge). Our experiments indicated that excess Ge atoms among palladium germanide alloy formation indirectly induce the abnormal out-diffusion of mass palladium atoms into Ge. Consequently, palladium germanide alloy on both n-type and p-type Ge form ohmic-like Schottky junctions. To identify this phenomenon, ?rst-principle calculations and technology computer-aided design simulation were used to evaluate the electrical in?uence of palladium atoms in Ge. We discovered that the activated palladium atoms in Ge induce large midgap bulk-trap states, which contribute to a severe increment of trap-assisted tunneling current at the palladium germanide/Ge junction.
关键词： Schottky junction,First-principles calculations,palladium germanide,technology computer-aided design,germanium,trap-assisted tunneling,fermi-level pinning effect
更新于2025-09-10 09:29:36
-
Enhancement of photoluminescence efficiency in GeSe ultrathin slab by thermal treatment and annealing: experiment and first-principles molecular dynamics simulations
摘要： The effect of thermal treatment and annealing under different temperatures from 100 °C to 250 °C on the photoluminescence spectroscopy of the GeSe ultrathin slab is reported. After the thermal treatment and annealing under 200 °C, we found that the photoluminescence intensity of A exciton and B exciton in GeSe ultrathin slab is increased to twice as much as that in untreated case, while is increased by ~84% in the photoluminescence intensity of C exciton. Combined by our experimental work and theoretical simulations, our study confirms the significant role of thermal treatments and annealing in reducing surface roughness and removing the Se vacancy to form more compact and smoother regions in GeSe ultrathin slab. Our findings imply that the improved quality of GeSe surface after thermal treatments is an important factor for the photoluminescence enhancement.
关键词： annealing,ultrathin slab,first-principles molecular dynamics,GeSe,photoluminescence,thermal treatment
更新于2025-09-10 09:29:36
-
First-principles investigation of the interface magnetic anisotropy of Fe/SrTiO<sub>3</sub>
摘要： Interface effects in the magnetic nanostructures play a critical role in the magnetic properties. By using the first-principles density functional theory calculations, we investigate the electronic and magnetic properties of Fe/SrTiO3 interfaces, in which both the nonpolar surface SrTiO3(001) and the polar surface SrTiO3(110) are considered. A particular emphasis is placed on the magnetic anisotropy energy (MAE). Compare MAE of the Fe/SrTiO3 interfaces and the corresponding Fe monolayers, we find the Fe/SrTiO3(001) interface decreases MAE, while the Fe/SrTiO3(110) interface increases MAE. The interface orbital hybridization and orbital magnetic moments are detailly analyzed to understand the different interface magnetic anisotropy. Our investigation indicates that interface engineering can be an effective way to modulate the magnetic properties.
关键词： Fe/SrTiO3 interfaces,interface orbital hybridization,first-principles calculations,magnetic anisotropy energy
更新于2025-09-09 09:28:46
-
Bandgap opening in graphene using alkali ions by first principles
摘要： Recently, bandgap opening at the Dirac point in graphene, formed on SiC(0001) surfaces, has been reported in different experiments, by deposition of positively charged alkali ions. This is clearly of great relevance for the countless practical applications of graphene in nano-electronic devices. By first principles calculations, based on the Density Functional Theory, the electronic band structure and the energetic properties are obtained for Na+, K+, and Cs+ ions interacting with graphene on SiC. We show that simple adsorption of alkali ions on intact graphene cannot give rise to a significant energy gap. An appreciable bandgap opening, similar to that observed in actual experiments, occurs instead due to the formation of Stone-Wales defects and substitutional defects (where positively charged alkali ions replace carbon atoms) that lead to a significant breaking of the charge symmetry among the carbon atoms of pristine graphene.
关键词： bandgap opening,graphene,alkali ions,Stone-Wales defects,substitutional defects,Density Functional Theory,first principles
更新于2025-09-09 09:28:46
-
Structural transformations and physical properties of (1-x) Na<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3-x</sub> BaTiO<sub>3</sub> solid solutions near morphotropic phase boundary
摘要： Piezoelectric and other physical properties are significantly enhanced at (or near) a morphotropic phase boundary (MPB) in ferroelectrics. MPB materials have attracted significant attention owing to both fundamental physics as well as the possibility of well-regulated energy and information storage devices which are dominated by lead (Pb)-based materials. Here, we report the crystal structure, Raman spectra, dielectric constant and polarization near the MPB of lead free (1-x) Na0.5Bi0.5TiO3 - x BaTiO3 (NBT - BT) (0.00 ≤ x ≤ 0.10) solid-solution, prepared by sol-gel auto combustion technique and sintered by microwave sintering technique. With the addition of BaTiO3 into Na0.5Bi0.5TiO3, it induces a structural phase transition from R3c (a single phase) to R3c+P4mm (a dual phase) close to x = 0.06 and 0.07 and transform to a high symmetry tetragonal phase P4mm at higher compositions (x = 0.08 to 0.10) as evident from our X-ray Rietveld refinement and Raman spectroscopic results. In the prepared solid solution, an anomalous enhancement of remnant polarization (2Pr0) was observed for x = 0.06 and 0.07, which has been explained based on the existence of the MPB. On the other hand, the value of coercive field EC0 was found to be decreased linearly from x = 0.00 to 0.06; it is constant for higher compositions. Further details of the ferroelectric properties on the electric field poled samples have been studied and compared with the as-grown (unpoled) samples. We perform first-principles calculations based on density functional theory that confirm a structural transition from a rhombohedral to a tetragonal phase under increasing x.
关键词： First-principles calculations,Crystal structure,Morphotropic Phase Boundary,Microwave sintering,Lead-free ferroelectric materials,Electrical properties,NBT-BT solid solution
更新于2025-09-09 09:28:46
-
Width-dependent phase crossover in transition metal dichalcogenide nanoribbons
摘要： Two-dimensional (2D) transition metal dichalcogenides MX2 (M = Mo, W; X = S, Se) monolayers exhibit two phases: the ground state 2H and the metastable 1T. Here, WSe2 and MoS2 monolayers have been studied, and we show by comprehensive first-principles calculations that the stability of the two phases can be switched in MX2 nanoribbons. The 2H phase is found to have increasingly higher energy than the 1T phase at a smaller ribbon width, and the width for favoring the 1T phase reaches up to 2.50 nm for WSe2. The phase crossover is due to higher coordination of edge M atoms in 1T phase than in 2H phase and an interesting electronic reconstruction of 1T lattice in the ribbon interior. The edge configuration of 1T phase diminishes the edge dangling bonds and thereby enhances the stability of MX2 nanoribbons. Our findings underscore the importance of edges in determining the structures of 2D MX2 and are crucial for their future scientific studies and potential applications.
关键词： nanoribbon,phase crossover,first-principles calculations,Transition metal dichalcogenide
更新于2025-09-09 09:28:46
-
First-principles study on the mechanics, optical, and phonon properties of carbon chains
摘要： Besides graphite, diamond, graphene, carbon nanotubes, and fullerenes, there is another allotrope of carbon, carbyne, existing in the form of a one-dimensional chain of carbon atoms. It has been theoretically predicted that carbyne would be stronger, stiffer, and more exotic than other materials that have been synthesized before. In this article, two kinds of carbyne, i.e., cumulene and polyyne are investigated by the ?rst principles, where the mechanical properties, electronic structure, optical and phonon properties of the carbynes are calculated. The results on the crystal binding energy and the formation energy show that though both are dif?cult to be synthesized from diamond or graphite, polyyne is more stable and harder than cummulene. The tensile stiffness, bond stiffness, and Young’s modulus of cumulene are 94.669 eV/ ?A, 90.334 GPa, and 60.62 GPa, respectively, while the corresponding values of polyyne are 94.939 eV/ ?A, 101.42 GPa, and 60.06 GPa. The supercell calculation shows that carbyne is most stable at N = 5, where N is the supercell number, which indicates that the carbon chain with 10 atoms is most stable. The calculation on the electronic band structure shows that cumulene is a conductor and polyyne is a semiconductor with a band gap of 0.37 eV. The dielectric function of carbynes varies along different directions, consistent with the one-dimensional nature of the carbon chains. In the phonon dispersion of cumulene, there are imaginary frequencies with the lowest value down to ?3.817 THz, which indicates that cumulene could be unstable at room temperature and normal pressure.
关键词： first-principles calculation,physical properties,electronic structure,carbyne
更新于2025-09-09 09:28:46
-
Nitrogen Trapping Ability of Hydrogen-Induced Vacancy and the Effect on the Formation of AlN in Aluminum
摘要： This paper presents the ternary interaction of N, H, and vacancy point defects and the nitrogen trapping ability of aluminum vacancies induced by hydrogen by means of DFT methods employed in VASP (Vienna Ab initio Simulation Package) and Abinit packages. The obtained vacancy formation energy of 0.65 eV is close to experimental values. Although the N–vacancy complex is unstable with the negative binding energy of ?0.51 eV, the stability of H–vacancy–N is proved by the positive binding energy of 0.59 eV and the appearance of the orbital hybridization in the density of state (DOS) of atoms connecting to this complex. Moreover, Al vacancies can trap more than 4 N atoms, which prevents the formation of aluminum nitride and subsequently affects not only the hardness of the Al surface but also many practical applications of AlN coating.
关键词： ternary point-defect interaction,first-principles calculations,alpha aluminum,superabundant vacancy
更新于2025-09-09 09:28:46
-
Prediction of Fundamental Properties of Semiconductors and Materials Exploration Using First-Principles Calculations
摘要： 昨今の資源?環境問題やエネルギー情勢を背景に，卓越した機能だけでなく，地球上に豊富に存在する元素により構成され，安価で高い環境調和性を示す新材料が望まれている．社会に役立つ「材料」へと昇華できる新物質を見いだすためには，的確に設計?探索の指針を立てることが重要であることは言うまでもない．そして次の関門が，いかに広い探索空間をカバーするか，その中からどのように有望な物質を絞り込むかである．最近では計算科学の進展とスーパーコンピュータの演算能力の向上により，第一原理計算等の計算科学手法を用いることで物質の安定性や特性を高精度かつ網羅的に予測できるようになってきた．これにデータ科学手法，更にはコンビナトリアル合成?評価等を連携させることで，新物質?新材料の開発を加速し，同時に膨大なデータの解析から設計?探索指針を得ようとする試みが世界各国で盛んになっている．いわゆる「マテリアルズ?インフォマティクス」によるアプローチである．
关键词： surfaces,point defects,interfaces,materials exploration,semiconductors,first-principles calculations
更新于2025-09-09 09:28:46