Formation Energy Analysis Research Articles

Constructing oxygen vacancies by selective anion doping in high entropy perovskite oxide for water splitting

High entropy perovskite oxide (HEPO) is a potential electrocatalyst for the oxygen evolution reaction (OER), but insufficient activity remains a problem. Oxygen vacancies can activate the lattice oxygen to induce the lattice oxygen-mediated mechanism (LOM), which can avoid the kinetic limitation present in adsorbate evolution mechanism (AEM), thereby improving the OER activity. Herein, we select the appropriate doping element (S) through analysis of ionic radius, electronegativity, and oxygen vacancy formation energy, and report an effective two-step oxygen vacancy strategy for introducing oxygen vacancies into HEPO through electrospinning and sulfurization treatment. This strategy optimizes the eg orbital filling electron number and significantly increases the active area, oxygen vacancy content and electroconductivity. Furthermore, the apparent pH dependence and the TMA+ inhibition phenomenon suggest the involvement of the LOM. Consequently, the resulting S/LMO-E has a lower overpotential (314 mV at 10 mA cm−2) and faster kinetics, and shows excellent stability. Meanwhile, the water splitting is achieved at 1.59 V to afford 10 mA cm−2 current density for S/LMO-E⎪⎢Pt/C, which is smaller than that of RuO2⎪⎢Pt/C (1.62 V). This work provides an attractive OER electrocatalyst for efficient water splitting to produce renewable hydrogen and opens a new way for the design of effective and stable high entropy material electrocatalysts.

Phase equilibria of CaO–Al2O3–CaO·TiO2 system at 1500 °C in hydrogen atmosphere

The phase diagram of CaO–Al2O3-TiOx system is of great importance in guiding the design of metallurgical slag systems for Al–Ti alloy steel, controlling Ti-bearing inclusions in molten steel, and regulating the mineral phase of vanadium-titanium magnetite. In the present work, the high temperature equilibration-quench technique was adopted, and the types and compositions of equilibrium phases were identified by Electron Probe Micro Analysis (EPMA) and X-ray diffraction (XRD). The isothermal section of CaO–Al2O3–CaO·TiO2 system at 1500 °C in H2 atmosphere was constructed for the first time. There are 7 three-phase fields, 10 two-phase fields, and a single liquid phase field. On this basis, according to the theoretical analysis of the crystal structure, the formation energy analysis based on first-principles calculations, and the related theories of defect chemistry, the formation mechanisms of CaTiO3 and Ca3Ti2O7 solid solution with were determined, respectively. Additionally, the experimental phase diagram was utilized to discuss the dissolution type and the equilibrium solubility of typical inclusions (Al2O3, Ti3O5, and CaO·TiO2) in Al–Ti alloy steel.

Exploring the Cs[formula omitted]LiLuCl[formula omitted] elpasolite scintillator for thermal-neutron detection: A comprehensive DFT and TD-DFT studies

In this study, we investigate the halide perovskite material Cs2LiLuCl6 using both density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches. Our analysis focuses on the structural, electronic, and optical properties of the material, conducted with the Quantum Espresso code. In order to confirm the structural stability of the material, we performed various tests including analysis of elastic constants, formation energy, tolerance factor, and phonon dispersion. Employing the generalized gradient approximation (GGA) and GGA+U, we determine that the material behaves as an insulator with a direct band gap of 5.3042 eV and 5.4245 eV, respectively. Additionally, DFT+U calculations were performed to study the dielectric function, reflectivity, absorption coefficient, and refractive index, revealing a high transmittance rate exceeding 90%. Under ideal conditions, the upper light yield (LYsc) is estimated to be 75411 ph/MeV and 73739 ph/MeV for the DFT and DFT+U methods, respectively. These results, along with the presence of lithium in Cs2LiLuCl6, highlight its potential for use in scintillation-based thermal-neutron detection applications.

Study of magnetic, thermoelectric, and mechanical properties of double perovskites Be2XH6 (X = Cr and Mn) for spintronic and hydrogen-storage applications

Metal hydrides are highly significant for hydrogen storage because of high gravimetric and kinetic factors. Therefore, the double perovskites hydrides Be2XH6 (X = Cr and Mn) have outstanding hydrogen storage capability with gravimetric hydrogen densities of 7.9 wt% and 7.6 wt%, respectively. Moreover, the DFT-based PBE-GGA and TB-mBJ potential have been implemented to systematically analyze the electronic, Curie temperature, and magnetic characteristics of Be2XH6 (X = Cr and Mn). The tolerance factor and formation energy analysis indicate the structural and thermodynamic stabilities. The band structures, density of states and Curie Weiss law ensure the above room temperature half metallic ferromagnetism with complete spin polarization. The ultralow lattice thermal conductivity and high thermoelectric performance also significantly increase their importance. Finally, the mechanical and thermodynamic behavior have also been addressed in detail. These conclusions are significant for future hydrogen storage growth increases in metal hydrates.

Study of mechanical, optoelectronic, and thermoelectric properties of Rb2ScAuZ6 (Z = Br, I) for energy harvesting applications

In the current article, the structural, mechanical, optoelectronic, and thermoelectric properties of Rb2ScAuZ6 (Z = Br, I) have been predicted using the density functional theory (DFT) approach. The tolerance factor, phonopy, and formation energy analysis validated the structural, dynamic, and thermodynamic stability of Rb2ScAuBr6 and Rb2ScAuI6, respectively. Likewise, the investigated elastic properties concluded that both materials exhibit mechanical stability and possess ductile characteristics. The directional-dependent elastic moduli revealed the anisotropy features. The indirect bandgaps determined by TB-mBJ approximation are 2.1 eV and 1.6 eV for Rb2ScAuBr6 and Rb2ScAuI6, respectively. Optical absorption, reflectivity, refractive index, and dielectric constants have been assessed in the energy range between 0 and 6 eV to ensure efficient absorption in the visible spectrum. Both materials have appropriate optical parameters for utilization in photovoltaic systems. Further, using the BoltzTraP code, the thermoelectric properties have been calculated to evaluate the thermoelectric efficiency. Both perovskites have lower lattice and electronic thermal conductivity, a higher Seebeck coefficient, and a higher figure of merit, making them ideal candidates for thermoelectric applications.

Study of electronic, mechanical, thermoelectric, and optical aspects of K2AlAg(Br/I)6 for solar cells, and energy storage applications

Double perovskite materials exhibit considerable potential in addressing global energy challenges and advancing renewable energy technologies. This study focuses on K2AlAg(Br/I)6 and employs a comprehensive DFT approach to explore its structural, mechanical, thermodynamic, optical, and thermoelectric properties. The structural and thermodynamic stabilities of K2AlAg(Br/I)6 are accurately examined through tolerance factor (τF) and formation energy analysis. The mechanical stability and ductile characteristics are affirmed by studying elastic constants, Passion's, and Pugh's ratios. Additionally, insights into hardness, Debye temperature, as well as transverse and longitudinal sound velocities contribute to a deeper understanding of the material's thermodynamic response. The band gap of K2AlAgBr6 is identified as 2.71 eV, which undergoes a reduction to 1.17 eV when Br is substituted with I, attributed to the pd-hybridization of cations and anions. Exploring optical properties reveals valuable information through dielectric constants ε(ω), refractive index (n(ω)), absorption (α(ω)), and reflectivity (R(ω)). Notably, absorption in both visible and ultraviolet ranges underscores the material's significance for solar cell applications. Furthermore, the computed ultralow lattice thermal conductivity and higher figure of merit are noteworthy outcomes, driven by the substantial Seebeck coefficient and electrical conductivity of the material. These results collectively highlight the exclusive and promising characteristics of K2AlAg(Br/I)6 in the area of renewable energy materials.

Electronic structure and optical properties of In- and Vacancy-doped 6H-SiC: a first-principles study.

The paper aims to investigative the cacusesand impactsof In- and Vacancy-doped to 6H-SiC, expecting that improving optical properties ofmaterials.Design-Using the first-principles calculations, we discuss the electronic structure and optical properties of different doped 6H-SiC systems. The results show that In-doped 6H-SiC becomes a direct bandgap p-type semiconductor and the energy bandgap is reduced from the intrinsic 2.059 to 1.515eV. We demonstrate the stability of the systems through the formation energy analysis, meanwhile identify their physical origins and discuss applications of all structures in electronic devices within optical analysis. Find the energy beginning values of the VSi-doped and VC-doped systems' optical absorption spectrums and extend to 0.4 2eV and 0.11eV respectively compared with the original 3.23eV. In the visible light region, the reflectivity images of the VC/VSi and (In, VSi)-codoped systems rise obviously. The optical properties of all doping systems were analyzed to be improved compared with the intrinsic, all above mentioned provide a theoretical basis for the fabrication of spintronic and optical devices.

First principle studies on structural, electronic, elastic, optical, and thermoelectric properties of XGeCl3 (X = Rb/Cs): Promising compounds for green energy application

AbstractThis study employed density functional theory (DFT) embedded in Wien2K code to evaluate the physical features of the XGeCl3 (X = Rb/Cs) cubic halide perovskites. The structural optimization has been performed considering generalized gradient approximation (GGA) and electronic properties have been computed considering modified Becke‐Johnson potential (mBJ). The formation energy and phonon dispersion analysis establish the stability of the investigated compounds. Mechanical stability is further confirmed by the computed diverse elastic coefficients. It has been discovered that the examined substances are naturally ductile. The refractive index, reflectivity, and absorption coefficient, are among the optical parameters that have been estimated and analyzed. Interesting results have been obtained for the transport properties of XGeCl3 (X = Rb/Cs). The XGeCl3 (X = Rb/Cs) exhibits a high Seebeck coefficient (X = Rb/Cs) and the largest figure of merit (about 0.99), indicating significant potential for thermoelectric applications.

Pressure-induced tuning of physical properties in high-throughput metal halide MSn2Br5 (M = K, Cs) perovskites for optoelectronic applications.

The physical properties of the ferromagnetic oxide perovskites MSn2Br5 (M = K, Cs) were thoroughly examined using the GGA + PBE formalism of density functional theory. The investigation includes a comprehensive characterization of these materials under hydrostatic pressures ranging up to 25 GPa. Our work represents the first theoretical framework for exploring the behavior of MSn2Br5 (M = K, Cs) under pressure, providing valuable insights into their properties. To ensure the thermodynamic and mechanical stability of the studied compounds, we justified their stability through the analysis of formation energy and Born stability criteria. Furthermore, we conducted a thorough examination of the mechanical features of MSn2Br5 (M = K, Cs) based on various parameters, such as elastic constants, elastic moduli, the Kleinman parameter, the machinability index, and the Vickers hardness. Pugh's ratio and Poisson's ratio data show a ductile behavior for both compounds under stress. Moreover, our analysis of the refractive index suggests that both materials hold significant potential as candidates for ultrahigh-density optical data storage devices, particularly when subjected to appropriate laser irradiation. This finding opens up exciting possibilities for utilizing MSn2Br5 (M = K, Cs) in advanced optical technologies.

Coinage metals doped 1T′ WS2 as efficient bifunctional electrocatalyst towards ORR and HER: A first principles study

The electrocatalytic activities of Cu, Ag and Au doped 1T′ WS2 as electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) in acidic medium are explored by means of first principles calculations. The stability of these doped systems are inspected in terms of formation energy and charge transfer analysis upon doping. Highest amount of charge transfer towards the dopant is observed for systems with lowest formation energy. For all the doped systems, charge is transferred to the dopant that substitutes the anionic S atom validating the doping scheme and stability of the doped systems. ORR proceeds only via the energetically efficient four electron pathway on Cu doped 1T′ WS2 with a monotonically exothermic free energy profile. In the case of Ag and Au doped structures, ORR occurs competitively via both two and four electron pathways due to the marginal free energy difference in the 2nd protonation step between these two pathways and produces both H2O or H2O2 competitively as the end product. Study of the effect of electrode potential variation on the free energy profiles reveals the overpotential for ORR on Cu, Ag and Au doped 1T′ WS2 to be 0.85 V, 0.80 V and 0.66 V respectively via the four electron pathway. Proneness of Cu doped 1T′ WS2 towards only the four electron pathway and low overpotential for ORR makes it the promising cathode electrocatalyst for ORR among the considered systems. Further study of the HER activity of Cu, Ag and Au doped 1T′ WS2 reveals the Gibbs free energy of H+ ion adsorption on Cu doped 1T′ WS2, Ag doped 1T′ WS2 and Au doped 1T′ WS2 to be −0.14 eV, −0.17 eV and 0.18 eV respectively indicating high efficiency of those system towards HER in acidic medium.

First-principles investigation for the hydrogen storage properties of XTiH3 (X=K, Rb, Cs) perovskite type hydrides

The perovskite-type hydride compounds are potential candidate materials in the field of hydrogen storage. This paper presents a systematical study of XTiH3 (X = K, Rb, Cs) using density functional theory. The analysis of formation energy, elastic properties and phonon dispersion curves indicate that all the studied materials are thermodynamically, mechanically and dynamically stable. By analyzing the B/G ratio, it is determined that these compounds are brittle materials. The electronic properties reveal that the XTiH3 compounds exhibit semi-metallic characteristics. The charge transfer characteristics of these compounds were analyzed using Bader partial charges. Moreover, the thermodynamic characteristics of these compounds were investigated and the dependence of their free energy, entropy and heat capacity on the temperature were analyzed. Finally, the gravimetric hydrogen storage capacities of KTiH3, RbTiH3 and CsTiH3 were calculated to be 3.36, 2.22 and 1.65 wt%, respectively. The hydrogen desorption temperatures of KTiH3, RbTiH3 and CsTiH3 were found to be 209 K, 161 K and 107 K, respectively. To our knowledge, this study represents the very first investigation of XTiH3 compounds and offers valuable references to this hydrogen storage material.

Honeycomb-like puckered PbTe monolayer: A promising n-type thermoelectric material with ultralow lattice thermal conductivity

Inspired by the superior thermoelectric performance of two-dimensional (2D) materials, the electrical transport and thermoelectric properties of honeycomb-like puckered PbTe monolayer were theoretically evaluated using the first-principles calculations and the semiclassical Boltzmann transport theory. The puckered PbTe monolayer is a direct gap semiconductor with wide bandgap of 2.251 eV within Heyd-Scuseria-Ernzerhof (HSE06) hybrid functional in combination with spin-orbital coupling (SOC) effect. Further analysis of formation energy, elastic constant, and ab initio molecular dynamics (AIMD) simulation prove the thermodynamic, mechanical and thermal stabilities of PbTe monolayer. The low thermal transport, small phonon group velocity, large Grüneisen parameters, and short phonon relaxation time greatly suppress the phonon transport and lead to low lattice thermal conductivity of ∼0.75 and ∼0.79 W/m K along the armchair and zigzag directions at 900 K, respectively. An optimal ZT = ~1.55 at the carrier concentration of 3.94 × 10 12 cm −2 is obtained for PbTe monolayer along zigzag direction at 900 K, which demonstrates the great advantages of honeycomb-like puckered PbTe monolayer as promising n- type thermoelectric material. Our present results would not only provide fundamental understanding of thermoelectric transport in honeycomb-like puckered PbTe monolayer, but also shed some light on the theoretical design of low dimensional PbTe-layered nanomaterials in thermoelectric applications. The honeycomb-like puckered PbTe monolayer with ultralow lattice thermal conductivity was designed for n -type thermoelectric material with excellent energy conversion efficiency. • The PbTe monolayer is direct semiconductor with wide band gaps. • The honeycomb-like puckered PbTe monolayer is dynamically and mechanically, and thermally stable. • The PbTe monolayer has low thermal conductivity, especially along armchair direction. • The puckered PbTe monolayer possesses excellent electron transport properties and power factor. • The n -type PbTe monolayer exhibit good thermoelectric properties, which can be used as potential materials for thermoelectric applications.

Construction of the Largest Metal-Centered Double-Ring Tubular Boron Clusters Based on Actinide Metal Doping

Metal doping has been considered to be an effective approach to stabilize various boron clusters. In this work, we constructed a series of largest metal-centered double-ring tubular boron clusters An@B24 (An = Th, Pa, Pu, and Am). Extensive global minimum structural searches combined with density functional theory predicted that the global minima of An@B24 (An = Th, Pu, and Am) are double-ring tubular structures. Formation energy analysis indicates that these boron clusters are highly stable, especially for Th@B24 and Pa@B24. Detailed bonding analysis shows that the significant stability of An@B24 is determined by the covalent character of the An-B bonding, which stems from the interactions of An 5f and 6d orbitals and B 2p orbitals. These results show that actinide metal doping is a feasible route to construct stable large metal-centered double-ring tubular boron clusters, offering the possibility to design boron nanomaterials with special physiochemical properties.

Ab initio investigation of properties and mobility of helium defects in La2Sn2O7 pyrochlore

The accumulated helium atoms mitigate the physical properties of nuclear waste forms through long-time radionuclide decay and thus cause the safety concern. In this work, first-principles calculations were carried out to investigate the effects of helium atoms on the structural, electronic, and mechanical properties of La2Sn2O7 pyrochlore. He atoms cause small volume swelling but no significant influence on its mechanical properties. The formation energy analysis suggests that octahedral interstitial sites are preferred. He interstitial may drive phase change from pyrochlore to the fluorite structure. The local electronic properties have also been analyzed to assess the impact of He clusters. The minimum energy pathway for helium to migration is identified as via O-O interstitial sites with a barrier of 1.39 eV. This work might offer a theoretical foundation for the He damage of the nuclear waste forms.

First-principles study of the electronic and optical properties of homo-doped 2D-hBN monolayer

The two-dimensional (2D) hexagonal boron nitride (h-BN) semiconductor has a wide bandgap and is made up of boron (B) and nitrogen (N) atoms arranged in a honeycomb lattice and connected by strong covalent bonds. We use first-principles based density functional theory (DFT), hybrid functional (GauPBE), and random phase approximation to explore the electronic and optical properties of pristine and 2D-(h-BN)1-xCx, x = 11 % and 22 % (carbon homo-doped 2D h-BN) monolayers. The formation energy analysis showed that the structural stability of carbon homo-doped 2D h-BN monolayer was better than 2D-(h-BN)1-xSx, x = 11 % and 22 % (sulfur homo-doped 2D h-BN) monolayer. The estimated band gaps in the carbon homo-doped 2D h-BN system were 5.9 (pristine), 4.25 (x = 11 % C), and 2.42 (x = 0.22 % C) eV, with the band gap decreasing as the concentration of the C atom increased. The polarization was parallel to the sheet as the carbon-homo doping concentration increased, and the band edge dropped to a minimal energy level, as validated by DFT + RPA calculations. Furthermore, the presence of LFE influence the optical properties of the homo-doped 2D h-BN.

Understanding electron transport in halogenated graphene nanoribbons and possible application as interconnects

To analyse the suitability of zigzag graphene nanoribbons (ZGNRs) as interconnects, the influence of halogen (F, Cl, Br, and I) passivation on ZGNRs has been analysed in terms of structural stability, electron transport, and thermal conductivity, as well as the performance parameters of the interconnects. The computation is performed using first-principle density functional theory with a non-equilibrium Green’s function approach, while the performance parameters of the interconnects such as delay and power delay product are computed using a HSPICE simulator tool. The formation energy analysis confirms the stability trend for halogen-passivated ZGNRs as F > Cl > Br > I. With moderate stability, the I- and Br-passivated ZGNRs have relatively better current–voltage characteristics in comparison to F and Cl. However, the Cl-passivated ZGNRs have relatively better interconnect parameters in comparison to other proposed halogenated systems (one edge and both edges), measured in terms of kinetic inductance and quantum capacitance. Another requirement of any good interconnect is less delay and less average power, which have also been computed and found to be relatively better in the case of Cl-passivated ZGNRs. Thus, among the halogen-passivated GNRs tested, those that are Cl-passivated defend their selection for interconnect applications well.

Controlling the magnetic alignment at the MnGa/Co2MnSi interface: A DFT study

The MnGa/Co2MnSi is a common electrode in Magnetic Tunnel Junctions (MTJ). We study the MnGa/Co2MnSi interfaces using spin-polarized Density Functional Theory. We have focused on the interface stability and the effect of the interface arrangements -at the atomic scale- on its electronic and magnetic properties. Depending on how the atomic species interact at the interface, the MnGa/Co2MnSi electrode can show either antiferromagnetic or ferromagnetic behavior, modulating the spin transfer through the system. Antiferromagnetic ordering appears due to Mn-Mn interlayer interactions across the MnSi-Mn interface and is thermodynamically stable for Co-poor and Mn-rich growth conditions. Mn atoms have magnetic moments of −2.97 μB and 2.31 μB. On the other hand, a ferromagnetic behavior could be engineered under Co-rich and Mn-poor conditions, as demonstrated by the interface formation energy analysis. Such magnetic ordering emerges at the Co-Ga interface since direct Mn-Mn interlayer interactions disappear; Mn atoms have magnetic moments of ∼ 3.00 μB and ∼ 2.8 μB for the Co2MnSi and MnGa films, respectively. Our findings lay the foundations to guide experimental efforts in designing electrodes that could potentially generate efficient tunneling behavior in perpendicular Magnetic Tunnel Junctions, which are the heart of novel MRAMs.

Is lithium brine water?

With the development of light and rechargeable batteries for electric vehicles, global demand for lithium has increased considerably in recent years. This has drawn more attention to how lithium is produced, especially on primary extraction operations such as those at the Salar de Atacama in Northern Chile. There are concerns that brine extraction at the Atacama could irreversibly damage the basin's complex hydrological system. However, differing opinions over the definition of water have frustrated basic action measures for minimizing impacts of operations like these. Some lithium industry stakeholders have historically described brine as a mineral, while others emphasize that brine is also a type of water in a complex network of different water resources. In this communication, we show that brines are undeniably a type of water. We support this position by investigating brine's water molecular structure using molecular dynamics simulations and comparing Gibbs formation energy of the brine using thermodynamic principles. Molecular dynamics show that the structure of water molecules in brine is similar to the structure of molecules in pure water at a pressure of 1.2 atm. The analysis of Gibbs formation energy shows that more than 99% of the brine's formation energy is directly from water, not dissolved minerals.

Heavy carrier doping by hydrogen in the spin-orbit coupled Mott insulator Sr2IrO4

Highly efficient carrier doping into the spin-orbit coupled Mott insulator ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ is achieved by low-energy hydrogen ion beam irradiation at low temperature. We demonstrate that heavy doping of hydrogen into a ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ epitaxial thin film induces a large increase in conductivity by band-filling control via electron doping, which is confirmed by Hall effect measurements. The introduction of a large amount of hydrogen and its distribution along the depth direction are clarified by nuclear reaction analysis. The doped interstitial and substitutional hydrogens act as electron donors with minimum perturbation to the lattice, as evidenced by crystal structural analysis and first-principles calculations of the defect formation energy for doped hydrogen. The hydrogen-doping method offers a strategy toward realization of novel quantum phases in strongly correlated spin-orbit entangled systems.

First principles investigation of the Structural, Mechanical, Electronic Properties and Debye temperature of W-Co alloys

In this paper, we have investigated the crystal structure, mechanical properties, electronic properties and Debye temperature of W-Co alloy according to the first principles method. The configurations investigated are W15Co1, W14Co2, W12Co4 and W8Co8 alloys, respectively. The results show that W-Co alloy still maintains a cubic lattice, and the lattice constant is lower than that of pure W. The formation energy analysis shows that the thermodynamic stability of W-Co alloy decreases with the increasing Co concentration. According to the mechanical stability criterion, it is concluded that W8Co8 alloy is mechanically unstable. Based on the elastic constant and other mechanical parameters analysis, the mechanical strength of W15Co1, W14Co2 and W12Co4 alloys is weaker than that of pure W. However, the B/G ratio and Poisson's ratio of W15Co1, W14Co2 and W12Co4 alloys are greater than that of pure W, indicating that Doping Co can improve the ductility of pure tungsten. Besides, the anisotropy, melting point and hardness, and Debye temperature of W-Co alloy is also evaluated.