Electronic Density Of States Research Articles

Insight into the physical properties of Rb2YCuX6 (X = Br and I) lead-free elpasolite for high-energy applications

This study explores the intriguing properties of lead-free Rb2YCuX6 (X = Br and I) elpasolite, a novel class of A2B’B‘X6 double perovskite materials, focusing on their structural, mechanical, and optoelectronic characteristics. The stability of the cubic structures was rigorously confirmed by calculating the tolerance factor, and octahedral factor, and employing the Birch-Murnaghan equation of states. Mechanical stability was confirmed through the examination of various parameters, revealing the materials as incompressible, hard, ductile, and anisotropic double perovskites. Analyzing the electronic band structure and density of states unveiled a distinctive indirect band gap of 2.46 eV for Rb2YCuBr6 and 2.12 eV for Rb2YCuI6, from L-X symmetry points. The optical parameters of these double perovskites were computed to evaluate their use in optical devices. Notably, their minimal light scattering, refractive index ranging from approximately 1.5 to 2, and broad absorption band within the visible spectrum make them highly suitable for optoelectronic applications, emphasizing their potential role in energy conservation and high-energy scenarios.

Density of Unoccupied Electronic States of the Ultrathin Layers of Dibromo-Bianthracene on the Surface of Layer-by-Layer Grown ZnO

Density of Unoccupied Electronic States of the Ultrathin Layers of Dibromo-Bianthracene on the Surface of Layer-by-Layer Grown ZnO

Theoretical modeling of the electronic structure and Fermi surfaces of Gd4Sb3 and GdSb2 compounds

Our theoretical modeling of the electronic structure in the intermetallic Gd4Sb3 and GdSb2 compounds has been done in the framework of density functional theory accounting for spin-orbit coupling. It revealed the metallic character of the summed total density of electronic states for both materials. The complicated Fermi surfaces were found in the half-metallic Gd4Sb3 compound which corresponds to the band structure. The GdSb2 material is obtained to be a bad metal with the low density of states near the Fermi energy, the Fermi surfaces of GdSb2 are found to have the cylindrical shape.

First-principles simulations of magnetic properties of Co- and Ni-doped ZnSe

We purposed to analyze the theoretical ab initio study of ferromagnetism and to estimate Curie temperature of Co2+ and Ni2+ 3d transition metal (TM) ions doped Zn1-x TM x Se compounds for 12.5 % and 6.25 % concentrations of impurity TM(Co, Ni) atoms. The calculations are carried out using the norm-conserving Fritz-Haber-Institute ionic pseudopotentials based on density functional theory within the local spin density approximation and Hubbard U (U(Znd)=4.5 eV; U(Sep)=3.8 eV) corrections. The analysis of the total and partial electron density of states shows the half-metallic ferromagnetic behavior with a half-metallic bandgap. The theoretically obtained total magnetic moments of TM(Co, Ni) doped Zn1-x TM x Se systems are equal to 3 μB and 4 μB, correspondingly.

First Principles Study of Electron Structure of La x Ba1- x MnO3 Crystals

In the framework of the density functional theory electronic band structure and density of states of LaxBa1-xMnO3 solid solutions containing different concentrations of La and Ba atoms, were studied using different exchange correlation functionals. Our calculation show that the band gap, which characterizes the properties of semiconductors, varies depending on the concentration of La and Ba atoms in the compounds. Using such a dependence, it is possible to make changes in physical properties depending on the concentration of cations.

Tuning the response trend of anaerobic ambience used Pd-based hydrogen sensor by engineering electronic band

Pd-based constituents have been widely used for sensing H2 due to the incredible selectivity, however, the sensitivity and measuring range in anaerobic ambience are largely limited for these using electronic signals. The variations between Pd and coincided hydride would typically increase resistance upon absorbing H2, whereas the intrinsic α-β phase transition alters the regularity of response features. Surprisingly, an inverse response has been detected by alloying Ag into Pd lattice, and this negative trend could be resulting from a new mechanism based on the experimental investigation and first-principles calculations. It is the contribution of modified Pd/Ag ratio, which optimizes the electronic band structure and density of states (DOS), thus a trade-off between free electron concentration and coincided scattering strength, would tune the response trend and make a switch. Consequently, the resistance of films with proper Ag contents, would be decreased at low H2 concentrations (10 ppm-4 vt.%), and the detection range can be widened as the trend reverses to be positive at high concentrations. These, combined with the ultralow detection limit of 10 ppm, and proportional sensor response values from − 0.5% of 10 ppm H2 to − 3.8% of 4 vt.% at 1 atm, confirm the promising virtues of anaerobic ambience used Pd-based sensors configuring inverse response. Furthermore, our study elucidates that alloying proper elements into Pd to modify the electronic band structure and DOS on Fermi energy, may be an effective strategy for promoting H2 sensing features.

Investigation of structural, electronic, magnetic, and mechanical stability of a non-trivial topology phase in compound full-Heusler alloys TiHfFeX (X=Al, Ga, In)

In this paper, we present studies relating to the structural, electronic, magnetic and mechanical properties of TiHfFeX ([Formula: see text], Ga, In) full Heusler alloys. We will use the GGA-PBE, TB-mBj, GGA-PBEsol, and GGA-WC approximation implemented in the density functional of the theory as integrated into the Wien2k software. However, the full Heusler alloys studied are considered in the ferromagnetic phase for different structural stabilities of the TiHfFeAl, TiHfFeGa and TiHfFeIn phases. types I, II or III, respectively. Calculation of band structures and total electron density of states shows that these alloys can both exhibit topologically non-trivial semi-metallic characteristics with energy bandgaps of 0.010[Formula: see text]eV, 0.014[Formula: see text]eV and 0.018[Formula: see text]eV. The electronic stability of ’such a Heusler structure will have nothing to do with its mechanical stability. Calculations reveal that the systems exhibit semi-metallic ferromagnetism. The elastic constants and the associated elastic moduli confirm its stability given by different elastic constants namely the Cauchy pressure, Poisson’s ratio, the anisotropy factor, Young’s modulus and the shear modulus.

Low-frequency electron–phonon interaction and superconductivity in L12 -type trialuminides Al3V

Superconductivity enhancement is often associated with phonon softening by doping or external pressure. In this paper, we report L12 -type trialuminides Al3V as a typical example belonging to this scenario. The electronic, phononic and superconducting properties have been studied by using the first-principle method. Under uniaxial compression, the superconducting transition temperature Tc of Al3V can be increased from ≈1.5 K to its maximum at ≈7.3 K when the lattice approaches the structural instability. A detailed investigation of Al3V reveals that the (V: d)-(Al: p) hybrid bands are strongly coupled to the phonon modes with lower frequency. The uniaxial compression induces a significant softening of the phonon mode with non-zero phonon line-width, and yet keeps the electron density of states near the Fermi level unchanged. This leads to a stronger electron–phonon coupling (EPC) and therefore a higher Tc . On the contrary, the L12 structure is more stable against the hydrostatic pressure and the phonon energy actually grows up when the hydrostatic pressure is increased. As a result, EPC becomes weaker and Tc can be reduced to ⩽ 0.3 K under high hydrostatic pressure. Our results present an interesting example that superconductivity can enhanced by tuning the softened phonon via pressure or doping.

Superconducting ternary hydrides in Ca-U-H under high pressure

The research on hydrogen-rich ternary compounds attract tremendous attention for it paves new route to room-temperature superconductivity at lower pressures. Here, we study the crystal structures, electronic structures, and superconducting properties of the ternary Ca-U-H system, combining crystal structure predictions with ab-initio calculations under high pressure. We found four dynamically stable structures with hydrogen clathrate cages: CaUH12-Cmmm, CaUH12-Fd-3m, Ca2UH18-P-3m1, and CaU3H32-Pm-3m. Among them, the Ca2UH18-P-3m1 and CaU3H32-Pm-3m are likely to be synthesized below 1 megabar. The f electrons in U atoms make dominant contribution to the electronic density of states around the Fermi energy. The electron-phonon interaction calculations reveal that phonon softening in the mid-frequency region can enhance the electron–phonon coupling significantly. The T c value of Ca2UH18-P-3m1 is estimated to be 57.5–65.8 K at 100 GPa. Our studies demonstrate that introducing actinides into alkaline-earth metal hydrides provides possibility in designing novel superconducting ternary hydrides.

Controlling charge density order in 2H−TaSe2 using a van Hove singularity

We report on the interplay between a van Hove singularity and a charge density wave state in 2H−TaSe2. We use angle-resolved photoemission spectroscopy to investigate changes in the Fermi surface of this material under surface doping with potassium. At high doping, we observe modifications which imply the disappearance of the (3×3) charge density wave and formation of a different correlated state. Using a tight-binding-based approach as well as an effective model, we explain our observations as a consequence of coupling between the single-particle Lifshitz transition during which the Fermi level passes a van Hove singularity and the charge density order. In this scenario, the high electronic density of states associated with the van Hove singularity induces a change in the periodicity of the charge density wave from the known (3×3) to a new (2×2) superlattice. Published by the American Physical Society 2024

Temperature shock to manipulate the optical properties of Al-doped ZnO films

We constructed the 2 × 2 × 2 Aluminum-doped Zinc Oxide (AZO) supercrystal cell structure and developed the temperature shock experiment at −40 °C–85 °C. The results showed that the temperature shock can increase the absorption rate of AZO, decrease the transmittance and the band gap of AZO, and change the density of electronic states near the Fermi level. The AZO films were also subjected to temperature shock of −40°C–85 °C, it shows that the transmittance and band gap of AZO films both decreased after temperature shock. The experimental results show that the temperature shock reduce the transmittance and the band gap width of the AZO films. The results are hoped to be helpful to understand the degeneration and improvement of the optical properties of AZO films under temperature shock loading and predict the performance of AZO films.

Electronic Structure of Li, Be, and Al Ultrathin Coverings on the Si(100) Surface

Within the framework of density functional theory and the pseudopotential method, calculations of the density of electronic states of the system “Si(100) substrate plus disordered two-dimensional metal layers (Li, Be or Al)” with a thickness of one to four single-atomic layers were carried out during growth at 0°K. It is shown that the electronic structure of the first single-atomic layers of these metals on Si(100) has band gaps. The maximum band gap was found in the Be-Si system (1.03 eV for a single-atomic layer). In this system, the band gap disappears when four single-atomic layers are deposited. In the Li-Si system (0.98 eV for a single-atomic layer) it disappears for two single-atomic layers. In the Al-Si–system (0.50 eV with four single-atomic layers), the band gap disappears for three single-atomic layers. This behavior of the band gap can be explained by the passivation of the substrate surface states and the peculiarities of the electronic structure of the adsorbed metals.

Adhesion, bonding and electronic properties of Ti/Zr doped c-BN(100)/Cu(100) interfaces: A first-principles study

Brazed monolayer cubic boron nitride (c-BN) tools are considered as promising tools for machining ductile metal materials. The interface between c-BN and filler alloys determines the properties of the tools to some extent. This paper uses first-principles calculations to study the atomic structures, work of adhesion, electronic properties, and density of states of c-BN(100)/Cu(100) clean and doped interfaces where the doping atoms are Ti/Zr. In this paper, four types of models are considered and calculated. The calculations reveal that Ti doping and Zr doping both increase the work of adhesion of the c-BN(100)/Cu(100) interface and the highest increase rate is 109 % and 83.4 %, respectively. The work of adhesion of c-BN(100)/Cu(100) interface doped with Ti is much higher than that doped with Zr and the electronic properties and density of states also prove this point of view. To sum up, Ti and Zr are both effective active elements to improve the performance of the c-BN/Cu interface, but, by comparison, Ti has better wettability to c-BN than Zr which provides an interpretation of the reported experimental results through the view of the atomic structures, work of adhesion, electronic properties and density of states.

Defects in <i>h</i>-BN: computer simulation of size effects

The influence of size effects on the properties of a hexagonal boron nitride (h-BN) monolayer containing CBVN, NBVN, and OBOBVN defects has been studied by first principles methods. These defects are potentially capable of generating single photons in quantum optics and quantum information devices. Size effects here mean the dependence of the studied model properties on the simulated fragment size of the 2D structure under periodic boundary conditions. Physically, this means that the properties of a monolayer depend on the distance between defects. This dependence allows us to judge how strongly the defects interact with each other and whether they interact at all. For technical applications, the characteristics of the band structure (band gap, spectrum and density of electron states induced by the defect in the band gap) and the atomic structure of the defect (defect formation energy, geometry in the equilibrium configuration), which form this band pattern, are important. In this work, these properties are studied by using the density functional theory with the basis of atom-like functions (SIESTA package) and plane waves (VASP package). The results obtained using both packages are consistent with each other. It has been established that the defects can be considered non-interacting, when the distance between them is ten unit cell parameters.

High-pressure properties of thallium orthovanadate from density-functional theory calculations

Thallium vanadate is the missing piece to fully understand the behavior of orthovanadates under high-pressure conditions. Here we report a computational study of TlVO4 under high pressure. Its properties and stability have been studied using the density-functional theory. We have found that TlVO4 undergoes at 2.7 GPa a phase transition from the CrVO4-type structure (described by space group Cmcm) to a wolframite-type structure (described by space group P2/c). In contrast to the behavior of isomorphic vanadates, a subsequent amorphization takes place beyond 6 GPa being it driven by dynamic instabilities. In addition to the structural analysis, we present a systematic study of elastic, vibrational, and bonding properties, as well as a characterization of the electronic band structure and electronic density of states. The distinctive behavior of TlVO4 is attributed to the contribution to the bonding of Tl 6s states. The implications of the observed phase transition and amorphization will be discussed.

Impact of rare earth (La, Pr, Eu) impurities on the perovskite SrTiO3 for efficient photocatalytic activity

Owing to the growing demand for environmentally friendly technologies across a wide range of fields, including energy, environment and medicine, photocatalytic materials have gained a lot of interest in recent years. First-principles calculations were used in order to examine a variety of physical characteristics such as electronic density of states, structural, optical, and photocatalytic properties of pristine and rare-earth (RE = La, Pr, Eu) doped SrTiO3. The reported electronic band gap of pristine SrTiO3 is Eg = 3.03 eV, which is reasonably consistent with prior theoretical and experimental studies. On the other hand, related to Sr(1−x)RExTiO3, the obtained energy band gaps are 2.75 eV, 2.80 eV, and 2.90 eV associated with Eu-SrTiO3, Pr-SrTiO3, and La-SrTiO3 respectively. The narrowing of the electronic band gap of the studied systems is due to the incorporation of RE-doped SrTiO3, which greatly enhanced the visible light absorption spectra and photocatalytic properties. Thus, it can be concluded that adding RE elements to this kind of materials, is a suitable choice for optoelectronic and photocatalytic applications.

Synergistic effect of Mn and B on the cohesive properties of grain boundaries in Ni3Al: A first-principles study

Ni-based superalloys are known as potential structural materials under extreme conditions due to their good high temperature properties. However, some alloys such as Ni3Al exhibit intrinsic brittleness which severely restricts their practical applications as structural materials. It is well known that the moderate addition of B can significantly improve the ductility of Ni3Al grain boundaries (GB) but restricted to the Ni-rich side. Adding Mn together with B can improve the ductility of Ni3Al in a wider composition range. To provide some fundamental understandings on such a cooperative effect, the segregation of Mn or/and B to the Ni3Al GBs and their effects on the cohesive properties of the GBs are systematically investigated by using a first-principles method. It is shown that B tends to segregate to the Ni-rich holes of the GBs, which means that B prefers to form stronger covalent bonds with the Ni atoms. The calculation of Griffith’s work shows its improved effect on the cohesion of the GBs. Different from site occupation tendency in bulk Ni3Al, Mn tends to segregate to the GBs and substitute the Ni sites at the GBs. It is interesting to notice that B can segregate to the Ni-deficient hole and improve the cohesive properties of the GBs in the presence of Mn substituting Ni atoms at the GBs. Whether at the Ni-rich holes or Ni-deficient holes of B segregation, Mn substituting the Al sites won’t take place at the GBs. The improvement of the ductility of composition-dependent Ni3Al extends from the Ni-rich side to the stoichiometric side with the co-doping of Mn and B. The electronic structure mechanism behind is discussed based on the calculated electronic density of states. It is suggested that the beneficial cooperative effect of Mn and B on the cohesive properties of the GBs is attributable to the increasing B-Al interaction.

Systematic study of the structural, electronic and optical properties of silicon nanowires

In this work we analyzed the structural, electronic, and optical properties of a set of silicon nanowires oriented in different directions, using the density functional theory. Structural optimization was performed in order to relax the atomic coordinates and cell parameters, after which the electronic band structure and density of states were obtained. Simultaneously, we computed the imaginary part of the dielectric function using the elements of the dipolar matrix. Furthermore, we related the transitions between the Van Hove singularities in the density of states with peaks in the absorption spectra, thus identifying relationships among them, which could be used to characterize the density of states by means of the absorption spectrum. The results showed that the electronic and optical properties depend on the diameter and orientation of the nanowires.

Electrochemistry at 2D and 3D nanoelectrodes: The interplay between interface kinetics and surface density of states

Heterogenous Electron Transfer (HET) at electrode-electrolyte interfaces depends strongly on the morphological features or geometry of the nanostructure used for modifying the electrode surface. A swift HET results in faster interface kinetics, which has significant impact on the development/calibration of electrochemical devices like biomolecular sensors, supercapacitors, batteries and electrochromic platforms. The interface electrochemistry depends strongly on the electronic Density of States (DOS) of electrode materials. Over the past years, the 2D electron gas nanomaterials - primarily graphene, Graphene Oxide (GO) and Reduced Graphene Oxide (RGO), have garnered significant interest in electrochemical applications due to promising DOS features. However, the electroanalytical dependency on DOS of 3D nanostructures such as Zinc Oxide Tetrapods (ZnOT) is yet unexplored. The current work focusses on a comparative electrochemical analysis of interface kinetics at RGO (2D) and ZnOT (3D) coated screen printed electrodes, with the intention of selecting the suitable material geometry. The analyses were performed using Cyclic Voltammetry (CV) and Electrochemical Impedance Spectroscopy (EIS). While the dependence of HET on DOS of RGO and ZnOT nanomaterials were studied using both DFT analysis and impedance-derived capacitance spectroscopy – the latter giving insights on quantum capacitance. It was observed that, the 2D RGO nanostructures exhibit higher surface DOS near the Fermi level, along with a high quantum capacitance (∼345 nF) as compared to 3D ZnOT (∼276 nF). This results in enhanced HET at the former, thereby indicating its suitability in developing futuristic electrochemical devices for various applications as desired.

Physical properties of vacancy-ordered double perovskites K2TcZ6 (Z = Cl, Br) for spintronics applications: DFT calculations.

Vacancy-ordered double perovskites (DPs) are emerging materials for spintronics due to their stable structures and non-toxic properties. In this study, we conducted a comprehensive investigation into the role of 4d electrons in Tc to understand their impact on the ferromagnetic properties of K2TcY6 (Y = Cl, Br). We have employed a modified Back and Johnson potential to assess electronic and magnetic characteristics and utilized the BoltzTraP code to investigate thermoelectric effects. Experimental lattice constants confirmed the presence of stable structures and formation energy estimates affirmed their thermodynamic stability. The Heisenberg model and density of electron states (DOS) at the Fermi level provides insights into Curie temperature and spin polarization. The presence of ferromagnetism is evident in the density of states, reflecting the transition of electron spins that support the exchange mechanism. The study delves into how electron functionality influences the control of ferromagnetism, considering exchange constants, exchange energies, hybridization process and the crystal field energies. Moreover, the exploitation of magnetic moments from Tc to K and Cl/Br sites takes precedence in driving ferromagnetism by exchanging electron spins rather than forming magnetic clusters. Additionally, to explore the optical characteristics of the compounds, we investigated their optical absorption, dielectric constants and refractive index within the energy range of 0-10 eV, ensuring absorption across both the visible and ultraviolet regions. Finally, we delve into the impact of the thermoelectric effect on both thermoelectric performance and spin functionality, taking into account factors such as the Seebeck coefficient, power factor, and electronic conductivity.