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Predicting the structure and stability of titanium oxide electrides
摘要： The search for new inorganic electrides has attracted significant attention due to their potential applications in transparent conductors, battery electrodes, electron emitters, as well as catalysts for chemical synthesis. However, only a few inorganic electrides have been successfully synthesized thus far, limiting the variety of electride examples. Here, we show the stabilization of inorganic electrides in the Ti-rich Ti–O system through first-principles calculations in conjunction with swarm-intelligence-based CALYPSO method for structure prediction. Besides the known Ti-rich stoichiometries of Ti2O, Ti3O, and Ti6O, two hitherto unknown Ti4O and Ti5O stoichiometries are predicted to be thermodynamically stable at certain pressure conditions. We found that these Ti-rich Ti–O compounds are primarily zero-dimensional electrides with excess electrons confined in the atom-sized lattice voids or between the cationic layers playing the role as anions. The underlying mechanism behind the stabilization of electrides has been rationalized in terms of the excess electrons provided by Ti atoms and their accommodation of excess electrons by multiple cavities and layered atomic packings. The present results provide a viable direction for searching for practical electrides in the technically important Ti–O system.
关键词： first-principles calculations,inorganic electrides,Ti-rich Ti–O system,structure prediction,CALYPSO method
更新于2025-09-04 15:30:14
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Tunable Direct Semiconductor Gap and High Carrier Mobility of Mo <sub/>6</sub> Br <sub/>6</sub> S <sub/>3</sub> Monolayer
摘要： Two-dimensional materials with direct semiconductor gaps and high mobilities can play an important role in future electronic and optical applications. Here we propose that Mo6Br6S3 monolayer as a new two-dimensional material is stable and can be exfoliated from corresponding layered bulk. Our first-principles results show that the monolayer has a direct semiconductor gap beyond 1 eV (between PBE and HSE values) and a very high electron mobility (6880 cm2V?1s?1), and these can be tuned through in-plane strain by applying uniaxial stress. Furthermore, we show that the Mo6Br6S3/graphene heterostructure makes a p-type Schottky barrier and the amplitude of band bending (0.03 eV) is extremely low compared to other similar junctions because the Mo6Br6S3 monolayer has a close work function to graphene. With all these useful properties and functions, the Mo6Br6S3 monolayer can be very promising for nanoelectronic and optical applications.
关键词： Mo6Br6S3 monolayer,p-type Schottky barrier,optical applications,Two-dimensional materials,electron mobility,high mobilities,first-principles,direct semiconductor gaps,nanoelectronic
更新于2025-09-04 15:30:14
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Investigation of Improvement of Electronic Properties and Ductility of RuAl2 Semiconducting Material by Boron Doping Using First-Principles Calculations
摘要： The occupation mechanism and influence of B doping on the electronic and mechanical properties of RuAl2 semiconducting compound have been investigated using first-principles calculations. Four possible B doping sites are considered. The results show that B-doped RuAl2 is thermodynamically stable. In particular, B element prefers to occupy B(4) site in comparison with other sites. Importantly, B doping improves the electronic properties of RuAl2 by shifting the Al 3p and Ru 4d states from the Fermi level (EF) to the valence band. Although B doping weakens the resistance to volume and shear deformation as well as the elastic stiffness of RuAl2, it improves the ductility due to the formation of Ru-B and Al-B bonds. Therefore, it can be concluded that B is a favorable doping element to improve the electronic properties and ductility of RuAl2 semiconducting compound.
关键词： Boron doping,RuAl2,First-principles calculations,Ductility,Electronic properties
更新于2025-09-04 15:30:14
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The Origin of Two-Dimensional Vertical Ferroelectricity in WTe <sub/>2</sub> Bilayer and Multilayer
摘要： In a recent report, room-temperature vertical ferroelectricity was experimentally shown in WTe2 bilayer, while its mechanism of ferroelectric switching without vertical ion displacements remains unclarified. In this work we reveal its origin by first-principles calculations that the polarization stems from uncompensated interlayer vertical charge transfer depending on in-plane translation, which can be switched upon interlayer sliding. The calculated results are consistent with experimental data, and similar switching mechanism can be applied to multilayer counterpart. Despite its small ferroelectric switching barrier and polarization, the in-plane rigidity of WTe2 layer gives rise to a high Curie temperature. A Moire pattern of ferroelectric domain superlattice can be formed and tuned upon a small-angle twist of bilayer, which is unique compared with traditional ferroelectrics. Similar interlayer translational ferroelectricity may exist in a series of van der Waals bilayers or even bulk phases.
关键词： Two-dimensional,WTe2,First-principles calculations,Ferroelectricity,Interlayer sliding
更新于2025-09-04 15:30:14
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Pressure tuning of the thermal conductivity of gallium arsenide from first-principles calculations
摘要： In this paper, the variation of the lattice thermal conductivity of GaAs under pressure within the range of 0–20 GPa at room temperature is investigated by combining first-principles calculations with an iterative solution of the phonon Boltzmann transport equation. Firstly, we calculated the lattice thermal conductivity of GaAs at 12 GPa, which increases by more than 37% in comparison with that under atmospheric pressure. The detailed analysis of phonon heat transport properties shows that the pressure contributes to increased phonon group velocity coupled with decreased phonon relaxation time, resulting in the pressure-induced nonlinear increase of the thermal conductivity of zinc blende GaAs. Besides, not only the structure but also the phonon heat transport properties of GaAs transform from isotropic to anisotropic beyond the phase transition pressure. This study provides a quantitative understanding of the thermal conductivity of GaAs considering pressure-induced phase transitions and highlights the importance of pressure in tuning lattice thermal conductivity, especially in pressure-induced phase change materials.
关键词： first-principles calculations,gallium arsenide,pressure,thermal conductivity,phonon Boltzmann transport equation
更新于2025-09-04 15:30:14
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Color-tunable and upconversion luminescence of Gd2O2S:Er,Tm phosphor: experimental investigations and first-principles calculation
摘要： The Er3+, Tm3+ co-doped gadolinium oxysulfide phosphors were prepared using solid-state reaction in vacuum. The crystal structure, morphology, and photoluminescence characteristics were, respectively, investigated by X-ray diffraction, transmission electron microscope, upconversion luminescence spectra and Commission Internationale de L’Eclairage diagram. Under 980 nm excitation, the quenching concentration of Er3+ was revealed to be 7 mol% with highest luminescence intensity and fluorescence lifetime. The emitting color of Gd2O2S:Er,Tm phosphors can be tuned by adjusting the concentration of Er3+ and Tm3+. First-principles calculation was employed to clarify the luminescence mechanism of the impurities doped in gadolinium oxysulfide host lattice by calculated band structure, density of states and absorption spectrum.
关键词： first-principles calculation,color-tunable,Gd2O2S:Er,upconversion luminescence,Tm
更新于2025-09-04 15:30:14
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First-principles study on the stability and properties of β-SiC/M+1AlC (M=Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; n=1,2) interfaces
摘要： In this work, first principles calculations are performed to investigate the structural, electronic, and mechanical properties of the interface between β-SiC ceramics and Mn+1AlCn (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; n = 1,2) phases, with particular focus on Ti3AlC2 and Ti2AlC. The interface between the β-SiC(111) and Tin+1AlCn (0001) (n = 1,2) surfaces is most likely a stable interface because of the small misfit in lattice constants. Six different interface models between β-SiC(111) and Tin+1AlCn(0001) are examined. The optimized interfacial distances are determined using the universal binding energy relation method, and then each model is fully relaxed to calculate work of adhesion. By comparison, it is determined that the junctions connecting the C-terminated SiC(111) and Ti-terminated Tin+1AlCn(0001) surfaces are the most stable structures. Then the electronic structures for this interface model of Ti3AlC2/SiC are analyzed from the density of states, atomic charges, total electron densities and electron density difference. The elastic moduli are also computed in this study, and the data show that the mechanical properties for the composite Tin+1AlCn/SiC slab are between those of bulk Tin+1AlCn and β-SiC, with enhanced plasticity. Finally, the results for β-SiC/Tin+1AlCn are extended to study the interfacial stabilization of β-SiC ceramics and the wider class of Mn+1AlCn phase coatings (M = Sc, Ti, V, Cr, Zr, Nb, Mo, Hf, Ta; n = 1,2). It is found that SiC ceramics may be effectively joined by Mn+1AlCn with stable interfacial chemical bonding, which provides a theoretical basis for the effective junction in SiC composites.
关键词： MAX phases,First-principles,SiC,Interfacial stabilization,Elastic modulus
更新于2025-09-04 15:30:14
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Impurity-derived <i>p</i> -type conductivity in cubic boron arsenide
摘要： Cubic boron arsenide (c-BAs) exhibits an ultrahigh thermal conductivity (j) approaching 1300 Wm(cid:2)1 K(cid:2)1 at room temperature. However, c-BAs is believed to incorporate high concentrations of crystal imperfections that can both quench j and act as sources of unintentional p-type conductivity. Although this behavior has been attributed to native defects, we show here, using optical and magnetic resonance spectroscopies together with first-principles calculations, that unintentional acceptor impurities such as silicon and/or carbon are more likely candidates for causing the observed conductivity. These results also clarify that the true low-temperature bandgap of c-BAs is 0.3 eV higher than the widely reported value of (cid:3)1.5 eV. Low-temperature photoluminescence measurements of c-BAs crystals reveal impurity-related recombination processes (including donor-acceptor pair recombination), and electron paramagnetic resonance experiments show evidence for effective mass-like shallow acceptors. Our hybrid density functional calculations indicate that native defects are incapable of giving rise to such signals. Instead, we find that group-IV impurities readily incorporate on the As site and act as shallow acceptors. Such impurities can dominate the electrical properties of c-BAs, and their influence on phonon scattering must be considered when optimizing thermal conductivity.
关键词： thermal conductivity,first-principles calculations,p-type conductivity,photoluminescence,impurities,cubic boron arsenide,electron paramagnetic resonance
更新于2025-09-04 15:30:14
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centers in amorphous
摘要： We investigate the charge-trapping behavior in nitrogen-deficient amorphous silicon nitride (a-Si3N4?x) using first-principles calculations. The amorphous ensembles with one nitrogen atom missing are generated through melt-quench procedures. The nitrogen deficiency mainly produces one Si—Si bond and one K center (Si dangling bond). The energy level of defect states indicates that the K centers act as possible trap sites. The transition levels of K centers are estimated, and it is found that the Hubbard U energy ranges from ?1.14 to 1.11 eV. Even though most K centers show positive U, the charge states of most centers in the ensemble are either positive or negative under the charge-neutrality condition, resulting in 'seemingly negative-U' behavior. This is consistent with the diamagnetic signal in experiments. The charge-injection energy of K centers is evaluated on the basis of the Franck-Condon approximation, and the average trap depths for electrons (1.33 eV below the conduction edge) and holes (1.54 eV above the valence edge) are in good agreement with experimental data.
关键词： K centers,Franck-Condon approximation,first-principles calculations,Hubbard U energy,amorphous silicon nitride,charge-trapping behavior
更新于2025-09-04 15:30:14
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All-Silicon Topological Semimetals with Closed Nodal Line
摘要： Owing to the natural compatibility with current semiconductor industry, silicon allotropes with diverse structural and electronic properties provide promising platforms for the next-generation Si-based devices. After screening 230 all-silicon crystals in the zeolite frameworks by first-principles calculations, we disclose two structurally stable Si allotropes (AHT-Si24 and VFI-Si36) containing open channels as topological node-line semimetals with Dirac nodal points forming a nodal loop in the kz=0 plane of Brillouin zone. Interestingly, their nodal loops protected by inversion and time-reversal symmetries are robust against SU(2) symmetry breaking due to very weak spin-orbit coupling of Si. When the nodal lines are projected onto the (001) surface, flat surface bands can be observed because of the nontrivial topology of the bulk band structures. Our discoveries extend the topological physics to the three-dimensional Si materials, highlighting the possibility to realize low-cost, nontoxic and semiconductor-compatible Si-based electronics with topological quantum states.
关键词： Zeolite frameworks,Node-line semimetals,Topological semimetals,Silicon allotropes,First-principles calculations
更新于2025-09-04 15:30:14