eV For Mg Research Articles

First Principle Investigations of Structural, Electronic and Thermal Properties of Pristine, Metal and Non-Metal Doped Silicene for Thermoelectric Applications

Silicene, a two-dimensional hexagonal silicon layer, exhibits exceptional electronic and thermoelectric properties. However, its application in semiconductors is hindered by its zeroband gap, which could be overcome by modifying its electronic properties through doping. In this paper, Density Functional Theory (DFT) calculations were performed to investigate the band gap opening in silicene by studying the effect of magnesium and sulphur doping on its electronic, structural and thermal properties. Pristine silicene has a lattice constant of 3.86 Å and a zero-band gap. Upon doping with 12.5% S and Mg atoms, the lattice constant modifies to 3.45 Å and 3.93 Å, respectively, resulting in a direct band gap opening. For 25% Mg and S doping, the result shows that Mg and S effectively alter the band structure and the band gap of silicene monolayer at various configurations. The maximum band gap was 0.98 eV and 1.22 eV for Mg and S doping into the meta position to the reference point R, respectively. The power factor significantly increases with doping, reaching 1.20 x 1011 WK-2m-1 and 1.40 x 1011 WK- 2 m-1 for 12.5% Mg and S doping compared to 7.4 x 1010 WK-2m-1 for pristine silicene. This substantial enhancement indicates improved thermoelectric performance, making silicene a promising candidate for thermoelectric applications. Results demonstrate that tuning the band gap through doping can simultaneously enhance the power factor, highlighting the potential of Mg/S-doped silicene for efficient energy harvesting and conversion.

Graphene-like BGe monolayer as anode material for metal-ions batteries: Computational predictions

Magnesium-, calcium- and potassium-ion batteries (MIBs, CIBs and PIBs) have attracted extraordinary attention as alternative batteries of lithium-ion batteries, due to their due to their abundancies, the low cost, safety. Herein, we investigated the suitability of BGe monolayer as anode material for MIBs, CIBs, and PIBs by using first-principles calculations in framework of density functional theory (DFT). The energy adsorption calculations and the charge transfer analysis show that the hollow site is the most favorable site for Mg, Ca, and K atoms adsorption on the BGe monolayer. In addition, the BGe monolayer has remained the same, preserving its metallic behavior after Mg, Ca and K atoms adsorption, which is suitable for batteries applications. The open circuit voltage ranges from 1.03 V to 1.02, 1.86 V to 1.67 V, and 2.85 V to 2.28 V for Mg, Ca, and K, respectively. Especially, the BGe monolayer exhibits a high theoretical specific capacity, up to 1284.63 mAhg−1 for Mg and Ca, and 642.31 mAhg−1 for K, which are higher than other monolayers. In addition, the BGe monolayer can provide a good charging-discharging processes with a low diffusion barrier of 0.80, 0.52, and 0.17 eV for Mg, Ca, and K-ion, respectively. All these properties indicate that the BGe monolayer is promising anode material for Mg/Ca/K ion batteries.

Bismuthene as a novel anode material of magnesium/zinc ion batteries with high capacity and stability: a DFT calculation.

In our research, we utilize density functional theory (DFT) to explore the properties of magnesium and zinc atoms adsorbed on bismuthene. Our findings indicate that the hollow site is the most favorable adsorption site for Mg and Zn atoms on bismuthene. The results indicate that Mg and Zn adsorption on the bismuthene surface results in significantly high conductivity, with notable adsorption energies of -3.38 eV for Mg and -3.91 eV for Zn. The bismuthene structure can adsorb 9 Mg and 18 Zn atoms with negative average adsorption energy. These findings suggest excellent stability of bismuthene during the adsorption of magnesium and zinc. Notably, we propose theoretical storage capacities of 2308 mA h g-1 for magnesium-ion batteries (MgIBs) and 4616 mA h g-1 for zinc-ion batteries (ZnIBs), while maintaining structural stability during the adsorption of these metal ions. The observed average open-circuit voltages for bismuthene are 0.01 V for Mg and 0.03 V for Zn, with the material retaining its metallic properties throughout the adsorption process. Furthermore, the calculated diffusion barriers for Mg and Zn are 0.1 eV and 0.21 eV, respectively. Our findings like storage capacity, diffusion energies, and low OCV surpass those of most studied two-dimensional materials, positioning bismuthene as a promising anode material for metal-ion rechargeable batteries.

Bare W-based MXenes (WCrC and MoWC) anode with high specific capacity for Li and Mg-ion batteries

The emergence of double transition metal MXenes (DTMs) has addressed the challenges associated with the high molar weight and non-metallic characteristics of early transition metal MXenes. In this study, we investigate the performance of WCrC and MoWC, DTMs, as anodes in Li/Mg-ion batteries (LIBs/MIBs) using first-principles calculations. The synergistic effect between the dual metal terminals is analyzed. Our findings reveal that the W terminal provides good electronic conductivity, while the Mo/Cr terminal reduces the molar mass, leading to enhanced energy density. The theoretical capacitance values are 648.81 mAh g−1 (WCrC anode) and 551.82 mAh g−1 (MoWC anode) in LIB, and 432.54 mAh g−1 (WCrC anode) and 367.88 mAh g−1 (MoWC anode) in MIBs. Both anodes exhibit low diffusion barriers with 0.045 eV for Li and 0.079 eV for Mg. They also maintain structural rigidity throughout the battery cycle. This study highlights the crucial role of the dual metal transition terminal synergistic effect in MXenes, influencing adatom adsorption behavior, reducing molar mass, and lowering diffusion barriers. These results contribute to the advancement of MXene surface engineering and offer valuable insights for battery research.

Energy Storage Mechanism of C12-3-3 with High-Capacity and High-Rate Performance for Li/Mg Batteries.

The low specific capacity and Mg non-affinity of graphite limit the energy density of ion rechargeable batteries. Here, we first identify that the monolayer C12-3-3 in sp2-sp3 carbon hybridization with high Li/Mg affinity is an appropriate anode material for Li-ion batteries and Mg-ion batteries via the first-principles simulations. The monolayer C12-3-3 can achieve high specific capacities of 1181 mAh/g for Li and 739 mAh/g for Mg, higher than those of most previous anodes. The Li storage reaction is an "adsorption-conversion-intercalation mechanism", while the Mg storage reaction is an "adsorption mechanism". The 2D carbon material of C12-3-3 displays fast diffusion kinetics with low diffusion barriers of 0.41 eV for Li and 0.21 eV for Mg. As a new carbon-based anode material, the monolayer C12-3-3 will promote the practical application of batteries with high-capacity and high-rate performance.

Mg acceptor doping in MOCVD (010) β -Ga2O3

In this Letter, in situ Mg doping in β-Ga2O3 was demonstrated via metalorganic chemical vapor deposition (MOCVD) epitaxy. The electrical insulating property of the Mg acceptors in β-Ga2O3 was found to be intrinsically activated in the as-grown Mg-doped β-Ga2O3 thin films. Growth conditions for MOCVD β-Ga2O3 were further explored and optimized at a lower growth temperature regime, leading to a better confinement of the Mg-doping profile. Detailed analysis of Mg diffusion characteristics revealed a diffusion barrier energy Ebarrier ∼ 0.9 eV for Mg in MOCVD β-Ga2O3, which is likely related to an interstitial-assisted process. Surface morphologies and electron transport were characterized on samples grown with different growth temperatures and Mg doping levels. The MOCVD growth method demonstrated its feasibility to grow semi-insulating Mg-doped β-Ga2O3 epilayers with controllable Mg incorporation while maintaining good material quality and smooth surface morphology. From capacitance-voltage charge profiling, it is verified that the Mg-doped buffer layer grown at the substrate-epilayer interface could effectively compensate the charge accumulation at the interface. The in situ acceptor doping of Mg in MOCVD β-Ga2O3 will provide versatility for designing β-Ga2O3 power devices.

Comparison of the Interfacial Reaction Kinetics and Plating Morphology of Lithium and Magnesium Anodes

Li dendrite growth is a critical safety issue for batteries with lithium metal anodes. Mg metal electrodes offer a promising way to overcome this safety limitation. Yao et.al. has observed that Li and Mg plating show different morphology, where Li plating is more dendritic but Mg plating is more faceted [1]. The difference of the morphology evolution of the plated Li and Mg is related to the interfacial reactions kinetics at the electrode and electrolyte interface. One major difference is that an electrical insulating but ionic conducting solid electrolyte interphase (SEI) always covers Li anode, but Mg electrode surface is believed to be SEI free[2]. Here, atomistic simulations are combined with phase-field model to evaluate the effect of interfacial reaction kinetics on the plated Li/Mg structural morphology. Reactivity of Li with liquid electrolytes, typically ethylene carbonate (EC), forms SEI layer on the Li metal. Magnesium aluminum chloride complex in tetrahydrofuran (THF) is one of the few electrolytes showing good reversible Mg deposition/stripping with a relatively large anodic stability (~3.1 V)[3]. Thus we considered Li/SEI/EC-electrolyte and Mg/THF-electrolyte interface models. Using both static first-principles calculations and ab initio molecular dynamics, the interfacial structures, de-solvation processes and Li+/Mg2+ ion energy landscapes at Li/SEI/EC-electrolyte and Mg/THF-electrolyte, and the effects of electric field on them were investigated. The preliminary results showed that the Li and Mg metal are all negatively charged at zero voltage, but the negative charge density of Li metal is more than that of Mg metal, which is due to SEI can block the electrons into electrolyte from anode. While the Mg plating free energy change for the electrode reaction is higher than Li due to its larger solvation energy (2.5 eV for Mg vs 1.2 eV for Li from thermodynamic cycle). Coupling with atomistic calculations, phase-field simulations were performed to investigate the Li/Mg plating morphological evolution from mesoscale. With thermodynamic and kinetic parametric inputs from first-principles calculation (i.e. interfacial energy and anisotropy of Li/SEI (Li2CO3), surface energy and anisotropy of Mg, diffusion coefficient of Li+ in SEI (Li2CO3), and relative difference in charge-transfer energy barrier of Li/Mg plating), our non-linear phase-field model captures the notable morphological evolution difference between dendritic Li plating and faceted Mg plating. Furthermore, the simulation results indicate that, among all possible parameters for Li/Mg electrodeposition processes, the plating charge-transfer energy barrier difference is the major contributing factor that accounts for the morphological discrepancy. Specifically, in our systematical tests on the impact of charge-transfer energy barrier on plating morphology (a range of 0.5-10 times of the Li plating reaction energy barrier height were tested), dendrites were prominently suppressed from around 2 times and faceted morphology (hexagonal for Mg) were produced at about 4 times. This study result fundamentally explains the origin of the Li/Mg plating morphological difference, and reveals that the proper elevation of the charge-transfer barrier height (e.g. by anodic surface treatment, protective coating, upgraded electrolyte, etc.) is a promising approach to dendrite suppression in Li metal batteries.

Ab initio molecular dynamics simulations of low energy recoil events in MgO

Low-energy recoil events in MgO are studied using ab intio molecular dynamics simulations to reveal the dynamic displacement processes and final defect configurations. Threshold displacement energies, Ed, are obtained for Mg and O along three low-index crystallographic directions, [100], [110], and [111]. The minimum values for Ed are found along the [110] direction consisting of the same element, either Mg or O atoms. Minimum threshold values of 29.5 eV for Mg and 25.5 eV for O, respectively, are suggested from the calculations. For other directions, the threshold energies are considerably higher, 65.5 and 150.0 eV for O along [111] and [100], and 122.5 eV for Mg along both [111] and [100] directions, respectively. These results show that the recoil events in MgO are partial-charge transfer assisted processes where the charge transfer plays an important role. There is a similar trend found in other oxide materials, where the threshold displacement energy correlates linearly with the peak partial-charge transfer, suggesting this behavior might be universal in ceramic oxides.

Mg and K Insertion in Glassy Amorphous Carbon vs Graphite as Potential Anode Materials: an Ab Initio Study

ABSTRACTIn search for effective negative electrodes for Mg- and K-ion batteries, we investigate the potential of glassy amorphous carbon by means of density functional theory calculations. Specifically, we provide the energetics for Mg and K insertion in two different structures of amorphous carbon. The insertion sites are found to be well distributed in energy, with insertion energies Ef vs. the cohesive energies of respectively Mg and K ranging from -1.1 to 2.8 eV for Mg and from -1.0 to 3.7 eV for K. To compare amorphous carbon to the most common structure of carbon (graphite), we study in addition the energetics associated with the insertion of Mg and K in graphite, for which two different stackings are considered for the two layers intercalating the Mg/K atom: the AB stacking which is most stable at the initial state of charge (in pure graphite) and the AA stacking which is most stable at the known final state of charge of K (KxC, x = 1/8). Already at the low concentration considered (x = 1/128), the insertion of Mg and K in graphite is found to favor the AA stacking, and to be thermodynamically unfavored (Ef positive with Ef = 1.9 eV for Mg and Ef = 0.7 eV for K). Amorphization appears therefore to provide insertion sites for Mg and K of lower (and negative) energies. The effect is of larger extent for Mg than for K, so much so that the insertion of Mg becomes more favored than that of K in amorphous carbon, although in graphite K is more easily inserted than Mg.

Role of Charge Transfer in Dehydrogenation of M(NH2BH3)2 (M = Mg, Sr)

The dehydrogenation mechanism of M(NH2BH3)2 (M = Mg, Sr) was studied by a first-principles method. The results show that the gas-phase energy barrier for the first H2 release is 2.15 eV via a N–H···B transition state and 1.35 eV via a Mg···H transition state for the second H2 release in Mg(NH2BH3)2. The barrier is 1.21 and 2.27 eV via a N–H···B transition state for the first and second H2 release in Sr(NH2BH3)2, respectively. For the dimer, both compounds release the first H2 via oligomerization and the corresponding barriers are 1.01 eV for Mg(NH2BH3)2 and 1.25 eV for Sr(NH2BH3)2. Further analysis of the charges of the transition states and the initial states leads to a general conclusion: for the same final state, the smaller the charge transfer, the lower the barrier. For Mg(NH2BH3)2, the reaction pathway is determined by the HOMO and LUMO orbitals of the initial state.

Materials properties of magnesium and calcium hydroxides from first-principles calculations

Recent experiments have revealed a good potential of applicability of multifunctional hydroxides X(OH)2 (X=Mg and Ca) in optoelectronic devices and emphasized the lack of fundamental understanding of their materials properties. This work presents systematic study of ground state properties, electronic structure, dielectric and optical properties of the materials by first-principles calculations within PBE-GGA and range-separated hybrid functional schemes as well as by using GW approximation. The relevant HSE06 hybrid functional mixing parameters were determined from a self-consistent adjustment to the electronic dielectric constant ∊∞. We show that the overall performance of our adaptation of the HSE06 functional via implementation of the modified amount of the Fock exchange is nearly best for the ground state properties as compared to the other relevant methods of Hartree–Fock and density-functional theory. Structural stability of the crystalline X(OH)2 hydroxides has been considered in static and dynamic aspects. The most important factors describing the bonding situation have been investigated, and a crystal-chemical integrity of the hydroxides has been analyzed. From electronic structure studies it was found that both materials are direct band gap insulators. Predictions for the fundamental band gaps were shown to be in the range of 7.7–8.3eV for Mg(OH)2 and 7.3–7.6eV for Ca(OH)2. The origin of the conduction and valence band states near the band edges has been studied in terms of orbital and site projected density of states as well as by comparison with the X-ray photoelectron spectroscopy measurements. It was shown that effective masses of carriers at the Γ-point in vicinity of the band extreme are strongly anisotropic and for the electrons are similar to those in the ZnO crystal. Optical properties of the bulk X(OH)2 hydroxides have been investigated in terms of the real and imaginary parts of the optical dielectric function calculated in GW approximation. Electronic character of anisotropy of optical properties has been clarified.

A computational study of the insertion of Li, Na, and Mg atoms into Si(111) nanosheets

Based on first principles calculations, we study the interaction of metal atoms (Li, Na, and Mg) with Si(111) nanosheets of different thicknesses. We show that the chemistry of the interactions is sensitive to both the nanosheet thickness and the dopant–surface distance. Both Li and Na atoms adsorb strongly on the nanosheet surface, accompanied by large charge transfers (∼0.9e) from the metal atoms to surrounding atoms. In contrast, Mg atoms have weak adsorption. Compared to bulk Si, we show that nanosheet Si is expected to improve the charge/discharge rate of Li/Na/Mg-ion batteries. Nevertheless, due to large insertion barriers (up to the prohibitive ∼2.1 and ∼3.1eV for Mg and Na, respectively) and significant energy differences between surface and sub-surface sites (∼1.0 and ∼1.9eV for Mg and Na, respectively), the theoretical capacities of Si for both Na-ion and Mg-ion batteries cannot be achieved at realistic charge/discharge rates.

Synthesis, Crystal Structure, and Properties of MgxB50C8 or Mgx(B12)4(CBC)2(C2)2 (x = 2.4−4)

Single crystals of a new magnesium boride carbide Mg(x)B(50)C(8) (x = 2.4-4) were synthesized from the elements in a metallic melt using tantalum ampules. Crystals were characterized by single crystal X-ray diffraction and electron microprobe analysis. The variation of the Mg content results from different reaction conditions. The composition Mg(∼3)B(50)C(8) is by far the most favored. It fulfills the electron counting rules of Wade and Longuet-Higgins and thus explains the light-green to yellow transparent color. The structure of Mg(∼3)B(50)C(8) (C2/m, Z = 1, a = 8.9384(12) Å, b = 5.6514(9) Å, c = 9.6021(13) Å, β = 105.86(1)°) consists of B(12) icosahedra. The icosahedra are interconnected by four exohedral B-B bonds to layers. The layers are connected to a three-dimensional covalent network by C(2) and CBC units and further exohedral B-B bonds. The Mg sites are partially occupied. Different site occupation factors cause the various compositions and colors (Mg(2.4)B(50)C(8), brown; Mg(4)B(50)C(8), black). The vibrational spectra show the modes of B(12) icosahedra and C(2) and CBC units as well. Measurements of the microhardness according to Vickers and Knoop revealed remarkably high values of H(V) = 3286 (32.0 GPa) and H(K) = 3165 (31.5 GPa), which exceed the values of B(4)C. Optical spectra reveal a band gap of 2.7 eV for Mg(∼3)B(50)C(8), in agreement to the observed color. This justifies an ionic description, and the formula can be written as (Mg(2+))(3)(B(12)(2-))(4)(CBC(+))(2)(C(2))(2).

OPTICAL AND ELECTRONIC PROPERTIES OF M2Si (M = Mg, Ca, Sr) GROWN BY REACTIVE DEPOSITION TECHNIQUE

Single phase M 2 Si ( M = Mg , Ca , Sr ) silicides were grown using Si substrates, by thermal treatment of the substrates in the vapors of the metallic sources, M , and the electronic structures and optical property of the silicides were investigated. The electronic band structures of the silicides were calculated using the first-principles total-energy calculation program in pseudopotential schemes with plane-wave basis functions. The calculated optical reflectance spectra were also deduced from the theoretical band structures, and roughly agreed with the experimental results except for the low reflectance intensity around 2 eV. This suggests that the energy band gap of the silicides roughly agree with the calculated values of 0.15, 0.31 and 0.35 eV for Mg 2 Si , Ca 2 Si and Sr 2 Si , respectively, within the underestimation of the band gap by the density functional calculation. The optical property of the silicides is also discussed in relation to the morphological structures of the silicides.

Adsorption and desorption of hydrogen in Mg nanoclusters: Combined effects of size and Ti doping

Using density functional theory formalism, we have investigated the interaction of hydrogen with pure and Ti doped Mg clusters. The objective of this study is two folds: (i) the reactivity of small Mg clusters in comparison to the extended Mg surface and (ii) the catalytic effect of Ti on the hydrogenation behavior. For Mg 55 cluster, the activation energy of hydrogenation is calculated to be 0.72 eV, which is 30% less than the bulk value of 1.04 eV. The interaction of hydrogen with Mg 55 and TiMg 54 clusters gives the binding energy of 0.217 and 0.164 eV, respectively. Moreover, the activation energy calculated by the elastic band method reveals that the dissociation barrier of hydrogen is 0.72 and 0.58 eV for Mg 55 and TiMg 54, respectively. Thus we could show a significant reduction in the activation barrier (almost 40%) of hydrogen dissociation in small clusters than the bulk. This has been attributed to the combined effects of the finite size of Mg clusters and the catalytic influence of Ti substitution. Further to underscore the hydrogen desorption mechanism, we have calculated the onset temperature of hydrogen diffusion using ab initio molecular dynamics simulation study on the hydrogenated Mg 55 cluster. The results reveal that at room temperature, the hydrogen atoms starts toggling from one Mg to another, which has been ascribed as the onset of hydrogen desorption.

Bound states of positrons and neutral atoms.

We use many-body perturbation theory to examine the interaction of positrons with atoms. Our calculations predict positron s-type bound states with binding energies 0.87, 0.23, 0.35, and 0.045 eV for Mg, Zn, Cd, and Hg atoms, respectively. This binding is due to the positron-atom polarization potential and virtual positronium formation. A simple criterion is used to find other atoms that are likely to form bound states with positrons. Among the most probable candidates are Ti, V, Cr, Mn, Zr, Nb, and Mo.

Ballistic-electron-emission microscopy and spectroscopy of GaP(110)-metal interfaces.

Ballistic-electron-emission-microscopy (BEEM) studies of Mg, Ni, Cu, Ag, and Au films on cleaved n-type GaP (110) show uniform Schottky-barrier heights across the surfaces, which varied from 1.02 eV for Mg to 1.41 eV for Au. BEEM images reveal areas of sharp current variations (contrast) that coincide with topographic gradients on the metal surfaces. Deduced Schottky-barrier heights depend on the transport model; a 5/2 power-law dependence of the BEEM current on applied voltage results if nonclassical transmission across the interface is included

The low-lying shape resonances in low-energy electron scattering with Be, Mg and Ca atoms

Static exchange (plus correlation-polarisation potential) calculations are performed for elastic low-energy electron scattering from Be, Mg and Ca atoms with attention to the low lying 2P and 2D shape resonances. The correlation potentials are calculated with and without a scaling factor. The scaling factor is adjustable as the alpha parameter in the X alpha theory, and is adjusted to produce the 2P resonance energy of e-Mg scattering in agreement with the experiment. The predictions with the parameter-free correlation-polarisation potential are a 2P resonance at 0.15 eV with width of 0.19 eV for Be, a 2P resonance at 0.065 eV with width of 0.05 eV for Mg and a 2D resonance at 1.5 eV for Ca with width of 3.0 eV. The 2P resonances of Be and Mg and the 2D resonance of Ca are produced at 0.24 eV, 0.14 eV and 1.75 eV with widths of 0.33 eV, 0.17 eV and 3.2 eV respectively, by using the scaled correlation potential. No 2P resonances are produced in the calculations for e-Ca scattering using either the parameter-free or scaled correlation potential, i.e. the authors give evidence for the existence of a stable negative ion of Ca in the 4s24p 2P state by using the theory used for electron scattering.

Contact resistivity of some magnesium/silicon and magnesium silicide/silicon structures

Transmission line model and end resistance measurements were made to determine the contact resistivity of Mg and Mg2Si contacts to Si doped n-type in the range 1018–1020 cm−3. The data are consistent with a barrier height of 0.4 eV for Mg and 0.52 eV for Mg2Si. The morphology, structure, and composition were studied using transmission electron microscopy.

Solubilities of Magnesium and Calcium in Silicon

The solubilities of the elements Mg and Ca are determined in monocrystalline silicon. The doping is accomplished using liquid‐phase epitaxy of silicon from Mg/Si or Ca/Si melts. Both Mg and Ca exhibit a strong retrograde solubility. The maximum solubility of Mg in silicon is ; that of Ca in silicon is . The segregation coefficients at the melting point of silicon are for Mg and for Ca. Both elements are mainly dissolved on substitutional lattice sites; the enthalpy of the solution is determined to be 0.9 eV for Mg and 1.2 eV for Ca.