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A body-centered cubic (bcc) FeCo(B) is a current standard magnetic material for perpendicular magnetic tunnel junctions (p-MTJs) showing both large tunnel magnetoresistance (TMR) and high interfacial perpendicular magnetic anisotropy (PMA) when MgO is utilized as a barrier material of p-MTJs. Since the p-MTJ is a key device of current spintronics memory, i.e. spin-transfer-torque magnetoresistive random access memory (STT-MRAM), it attracts attention for further advance to explore new magnetic materials showing both large PMA and TMR. However, there have been no such materials other than FeCo(B)/MgO. Here, we report, for the first time, PMA in metastable bcc Co-based alloy, i.e. bcc CoMnFe thin films which are known to exhibit large TMR effect when used for electrodes of MTJs with the MgO barrier. The largest intrinsic PMAs were about 0.6 and 0.8 MJ/m3 in a few nanometer-thick CoMnFe alloy film and multilayer film, respectively. Our ab-initio calculation suggested that PMA originates from tetragonal strain and the value exceeds 1 MJ/m3 with optimizing strain and alloys composition. The simulation of the thermal stability factor indicates that the magnetic properties obtained satisfy the requirement of the data retention performance of X-1X nm STT-MRAM. The large PMA and high TMR effect in bcc CoMnFe/MgO, which were rarely observed in materials other than FeCo(B)/MgO, indicate that bcc CoMnFe/MgO is one of the potential candidates of the materials for X-1X nm STT-MRAM. IMPACT STATEMENT: We discovered large perpendicular magnetic anisotropy, ~0.8 MJ/m3, in metastable alloys, which are also known to exhibit large tunnel magnetoresistance, demonstrating new candidate for spintronic memory applications. [ABSTRACT FROM AUTHOR]

Photoluminescence quantum yield (PL QY) of colloidal quantum dots (QDs) can be improved by growing a shell, but it is rather limited if the shell thickness exceeds a threshold. Lattice mismatch between the core and shell is known to determine this critical shell thickness, securing QDs from defect formation through strain release. However, it cannot explain the recently reported high efficiency QDs with giant shells. Based on CdSe/ZnSe thick shell QDs, this study aims to identify the culprit limiting PL QY. In the shell growth process, the gradual reduction in PL QY is accompanied by a low‐energy tail emission, but the additional compressive strain by the outmost shell eliminates such abnormalities. It is revealed that the zinc vacancy in the shell provides shallow hole trap states. The computational study successfully explains the hole‐accepting zinc vacancy states above the CdSe 1Shh state, raised by compressive strain along radial direction. Additional hydrostatic compressive strain lifts the 1Shh state for this strained heterostructure to minimize the energetic gap with the zinc vacancy states. The finding suggests that critical shell thickness can be limited by atomic vacancy incorporated during shell growth, not by formation of misfit dislocation caused by strain release. [ABSTRACT FROM AUTHOR]

In this work, we study the equiatomic quaternary Heusler alloy (EQHA) CoFeCrP using two methods: density functional theory (DFT) and Monte Carlo simulations. The DFT method allowed us to illustrate the structural, electronic, and magnetic properties of this alloy. The ground state phase diagrams have been presented to show the stable configurations in different physical parameter planes. On the other hand, the Monte Carlo simulations, performed under the Metropolis algorithm, permitted to deduce the critical the behavior of the EQHA CoFeCrP. The structural properties results show that the phase of type I, of this alloy is the most stable configuration. In addition, the band structures and density of states calculations results show that this compound exhibits a half-metallic character with a 100% of spin polarization (SP) at the Fermi-level. The total magnetic moment of the Heusler compound is found to be 4.00 µB. Moreover, it is found that the Slater-Pauling is well described for this alloy. Our results show that this material is a potential candidate for the spintronic applications. This is due to its half-metallicity, its high spin moments, its complete SP polarization, and its high Curie temperature. [ABSTRACT FROM AUTHOR]

Strain engineering is generally employed as an efficient means of tuning the physical properties of a target compound. In this research paper, we investigated the effect of three axial stretches on the structural, electronic, optical, and thermoelectric properties of inorganic Ge-based halide perovskites LiGeBr3. Computations were carried out using Density Functional Theory (DFT) and the semi-classical Boltzmann transport theories. The electronic investigation indicated that LiGeBr3 perovskite exhibits a direct bandgap of 0.480 eV. The findings suggest that the bandgap is highly responsive to strain, which improves the absorption ability in the visible light range (300–500 nm). The relative stability of the strained compounds and the feasibility of their synthesis were robustly demonstrated by the negative formation energies. The transport features were assessed as a function of temperature and yielded interesting results. The electrical conductivity was considerably enhanced under strain, and the highest figure of merit was found at low temperatures (approximately 0.741). Our theoretical discovery proved that strain is an enormously exciting technique for extending semiconductor applications and boosting thermoelectric and solar cell devices. [ABSTRACT FROM AUTHOR]

In this work, we investigate the hydrogen-storage properties of Zr-decorated γ-graphyne monolayer employing Density Functional Theory (DFT) for green energy storage. We predict that each Zr atom decorated on graphyne sheet (2D) can adsorb up to seven H 2 molecules with an average adsorption energy of −0.44 eV/H 2 , leading to a hydrogen gravimetric density of 7.95 wt%, and desorption temperature of 574 K, particularly suited to fuel-cell applications. Decorated Zr atom strongly attached to graphyne due to charge transfer from Zr to graphyne sheet. Hydrogen molecules adsorb on Zr decorated graphyne due to Kubas type of interactions. The 4.05 eV diffusion energy barrier for the movement of Zr atoms may avoid the metal-metal (Zr–Zr) clustering. The stability of Zr+γ-graphyne is confirmed by performing ab-initio molecular dynamics simulations at room temperature and at estimated average desorption temperature. Hence, our calculations show that Zr functionalized on γ-graphyne could be a promising solid-state hydrogen storage material. [Display omitted] • Zirconium binds on graphyne with energy −3.89eV at the hexagonal position. • Each Zr adsorbs 7H2 molecules leading to 7.95 gravimetric weight % of hydrogen. • Average adsorption energy and desorption temperature are −0.44eV/H2 and 574 K. • Presence of diffusion energy barrier (4.05eV) may avoid metal-metal clustering. • Stability of structure verified from AIMD simulations. [ABSTRACT FROM AUTHOR]

Nuclear moments of the antimony isotopes 113−133Sb are measured by collinear laser spectroscopy and used to benchmark phenomenological shell-model and ab initio calculations in the valence-space in-medium similarity renormalization group (VS-IMSRG). The shell-model calculations reproduce the electromagnetic moments over all Sb isotopes when suitable effective g-factors and charges are employed. Good agreement is achieved by VS-IMSRG for magnetic moments on the neutron-deficient side for both odd-even and odd-odd Sb isotopes while its results deviate from experiment on the neutron-rich side. When the same effective g-factors are used, VS-IMSRG agrees with experiment nearly as well as the shell model. Hence, the wave functions are very similar in both approaches and missing contributions to the M1 operator are identified as the cause of the discrepancy of VS-IMSRG with experiment. Electric quadrupole moments remain more challenging for VS-IMSRG.

The crystal family of potassium titanyl phosphate (KTiOPO 4 ) is a promising material group for applications in quantum and nonlinear optics. The fabrication of low-loss optical waveguides, as well as high-grade periodically poled ferroelectric domain structures, requires a profound understanding of the material properties and crystal structure. In this regard, Raman spectroscopy offers the possibility to study and visualize domain structures, strain, defects, and the local stoichiometry, which are all factors impacting device performance. However, the accurate interpretation of Raman spectra and their changes with respect to extrinsic and intrinsic defects requires a thorough assignment of the Raman modes to their respective crystal features, which to date is only partly conducted based on phenomenological modelling. To address this issue, we calculated the phonon spectra of potassium titanyl phosphate and the related compounds rubidium titanyl phosphate (RbTiOPO 4 ) and potassium titanyl arsenate (KTiOAsO 4 ) based on density functional theory and compared them with experimental data. Overall, this allows us to assign various spectral features to eigenmodes of lattice substructures with improved detail compared to previous assignments. Nevertheless, the analysis also shows that not all features of the spectra can unambigiously be explained yet. A possible explanation might be that defects or long range fields not included in the modeling play a crucial rule for the resulting Raman spectrum. In conclusion, this work provides an improved foundation into the vibrational properties in the KTiOPO 4 material family. [ABSTRACT FROM AUTHOR]

In this work, an ab-initio calculation is used to investigate the elastic constants and some other mechanical and thermal parameters of tetragonal Cu2ZnSnS4 (CZTS) quaternary semiconducting bulk material in Kesterite (KS) and Stannite (ST) phases. The Quantum Espresso code within the Ultra Soft pseudo potentials (USPP) and the local density approximation (LDA) approach were used in the calculation. Firstly,, studies are started with the prediction of the elastic stiffness constants Cij and the normal and shear anisotropy factors. Then some other mechanical moduli, especially the isotropic bulk modulus B, the shear modulus G, the Young modulus E, the Poisson’s ratio ν, and the Pugh’s criteria (G/B) are delivered. The analysis of the mechanical stability criteria at equilibrium shows that our elastic stiffness constants Cij of CZTS material obey all the stability conditions. Additionally, some other parameters of the CZTS semiconductor, especially: the Vickers hardness HV, the sound velocity, the Debye temperature θD and the melting temperature Tm were also calculated. The obtained values of the elastic constants Cij and other mechanical and thermal parameters agree well with experimental and other theoretical results of the literature. The Debye temperature θD of the KS phase was found at around 332.7 K, and that of the stannite phase was found equal to 329.1 K, respectively.

Structural, electronic, and elastic properties of SrFCl, one of the alkaline-earth fluorohalides, under high pressure were investigated using the Siesta Package Program within the framework of density functional theory. SrFCl crystallizes in a tetragonal matlockite type structure belonging to the space group P4/nmm at ambient conditions. The phase transformation from a tetragonal matlockite type structure to an orthorhombic type structure belonging to the space group Pmmn occurred in the presence of gradually increasing simulation pressure. The values of lattice parameters, shear modulus, Young's modulus, and bulk modulus, for the obtained structures of SrFCl were investigated. The transition pressure value was calculated by total energy and enthalpy calculations. The electronic properties of SrFCl were also calculated. Band gaps of 6.52 eV for the P4/nmm phase and 3.55 eV for the Pmmn phase were obtained. Thus, it was concluded that the P4/nmm and Pmmn phases of SrFCl have an insulator and a semiconductor character, respectively. In addition to these studies, the mechanical stability of SrFCl was investigated by calculating elastic constants. As a result of this calculation, both phases of SrFCl were mechanically stable. [ABSTRACT FROM AUTHOR]

Full Heusler compounds are a promising material for the next generation of spintronic devices. Here, we present the first investigation of the structural, magnetic, electronic, and thermoelectrical properties of full Heusler compounds CoXZeGe (X = Rh, Ru). The investigation was performed by using both the Generalized Gradient Approximation (GGA) and the Modified Becke–Johnson (mBJ) approximation. Both compounds were crystallized in the Cu2MnAl prototype and in the ferromagnetic phase. The calculated magnetic moment for CoRuZeGe and CoRhZeGe are 1 µB, and 2 µB, respectively. In addition, the band electronic and density of the states' structures prove the half metallic behavior of these compounds with full spin polarization which makes them an excellent choice for the field of spintronics. Moreover, the thermoelectric properties such as the Seebeck coefficient (S), electronic thermal conductivity (κe/τ), power factor, and figure of merit (ZT) have been studied and discussed in detail. Consequently, the investigated compounds were identified as candidate materials for high technological applications. [ABSTRACT FROM AUTHOR]

Electric field reconstruction at interfaces plays a crucial role in device performances controlling, for example, Schottky potential barrier and interfacial Rashba effect. Here, scanning transmission electron microscopy (STEM) and ab‐initio calculation are used to estimate the atomic‐scale and large‐scale potential reconstruction at the interface between a metallic oxide SrRuO3 (SRO) thin film and an insulating DyScO3 (DSO) substrate. The intensity and the symmetry of the large‐scale electrostatic reconstruction at the interface is probed by 4D‐STEM discussing the center‐of‐mass shift for different angular ranges detection. Numerical simulations indicate that thermal diffuse scattered (TDS) electrons can be sensitive to large‐scale electric field and experiments based on these diffused electrons near the interface confirm that the electric field extends more in the insulating DyScO3 (DSO) side. The magnitude of the electrostatic drop at the interface estimated by the 4D‐STEM experiment is in accordance with the ab‐initio values for a p‐type reconstruction of the interface plane. Furthermore, an atomically resolved TDS potential asymmetry is observed in real‐space at the SRO/DSO interface by 4D‐STEM. This asymmetry is associated with the formation of a local ferroelectric type dipole at the interfacial unit‐cell revealing unambiguously the balance evolution between antiferrodistortive and ferroelectric instabilities at the interface between a metallic SRO and an insulating DSO. [ABSTRACT FROM AUTHOR]

Abstract Electric field reconstruction at interfaces plays a crucial role in device performances controlling, for example, Schottky potential barrier and interfacial Rashba effect. Here, scanning transmission electron microscopy (STEM) and ab‐initio calculation are used to estimate the atomic‐scale and large‐scale potential reconstruction at the interface between a metallic oxide SrRuO3 (SRO) thin film and an insulating DyScO3 (DSO) substrate. The intensity and the symmetry of the large‐scale electrostatic reconstruction at the interface is probed by 4D‐STEM discussing the center‐of‐mass shift for different angular ranges detection. Numerical simulations indicate that thermal diffuse scattered (TDS) electrons can be sensitive to large‐scale electric field and experiments based on these diffused electrons near the interface confirm that the electric field extends more in the insulating DyScO3 (DSO) side. The magnitude of the electrostatic drop at the interface estimated by the 4D‐STEM experiment is in accordance with the ab‐initio values for a p‐type reconstruction of the interface plane. Furthermore, an atomically resolved TDS potential asymmetry is observed in real‐space at the SRO/DSO interface by 4D‐STEM. This asymmetry is associated with the formation of a local ferroelectric type dipole at the interfacial unit‐cell revealing unambiguously the balance evolution between antiferrodistortive and ferroelectric instabilities at the interface between a metallic SRO and an insulating DSO.

Optoelectronic properties of the quaternary Heusler Ni2MnGa alloy were analyzed by using the full-potential linearized augmented-plane wave (FPLAPW), which is based on density functional theory. We will use the generalized gradient approximation (GGA) and other methods. However, the study of electronic and magnetic properties indicated that the Ni2MnGa is a ferromagnetic material that has a semi-metallic characteristic with a Curie temperature approximately 358 K obtained by the GGA method and thus is considered a promising candidate for incorporation into spintronic devices. Also, the prediction of a more stable structure to this material is obtained by the uniaxial deformation of the basic structure in the austenite phase, producing a tetragonal structure in the martensitic phase at a transformation temperature equal to 132 K. Finally, the optical and thermoelectric properties of the Ni2MnGa alloy show a noticeable structural dependence for the weak values of the photon energies. [ABSTRACT FROM AUTHOR]

The electric quadrupole moment of 49Sc was measured by collinear laser spectroscopy at CERN-ISOLDE to be Qs=−0.159(8) eb, and a nearly tenfold improvement in precision was reached for the electromagnetic moments of 47,49Sc. The single-particle behavior and nucleon-nucleon correlations are investigated with the electromagnetic moments of Z=21 isotopes and N=28 isotones as valence neutrons and protons fill the distinctive 0f7/2 orbit, respectively, located between magic numbers, 20 and 28. The experimental data are interpreted with shell-model calculations using an effective interaction, and ab-initio valence-space in-medium similarity renormalization group calculations based on chiral interactions. These results highlight the sensitivity of nuclear electromagnetic moments to different types of nucleon-nucleon correlations, and establish an important benchmark for further developments of theoretical calculations.

Thermodynamic stability of the hexagonal delta phase has been discussed for the U-50 wt% Zr alloy composition based on the XRD, FESEM, and EDS results, further corroborated by the ab-initio calculations. It has been shown that U-50 wt% Zr composition falls into a two-phase region in the U–Zr phase diagram at about 573 K, in contradiction to the published phase diagram. Crystallographic structure of the delta phase in terms of the atomic occupation has been elucidated using the near-neighbour analysis obtained from the EXAFS results. It is shown here that the (111) plane collapse mechanism of the parent bcc phase is not complete in the delta phase even after the sample was aged for 864 ks (240 h) at 573 K. [ABSTRACT FROM AUTHOR]

Experimental and theoretical studies enabled the reveal of patterns of the microstructure formation in the surface layer of Ti-6Al-4V titanium alloy subjected to ultrasonic impact treatment. The mixed amorphous and nanocrystalline structure of the 200 nm thick uppermost surface layer of titanium dioxide TiO2 was demonstrated using transmission electron microscopy. The 5 µm thick intermediate layer containing nanocrystalline α grains, and the 50–60 µm thick lower layer containing fragmented α-Ti grains with retained β phase were also observed. The refinement of the β-Ti phase during ultrasonic impact treatment was accompanied by the formation of the orthorhombic (α″) martensitic phase. Molecular dynamics simulation of strains of a vanadium-doped titanium crystallite subjected to ultrasonic impact treatment revealed the formation of striped dislocation substructures as well as the development of reversible β→α phase transformations. Ab initio calculations of the atomic structure of V-doped Ti crystallites containing α, β or α″ phases of titanium were carried out. On the basis of the results of the experimental observations, a molecular dynamics simulation and ab initio calculations a mechanism was proposed, which associated the development of the strain-induced β→α″ phase transformations in Ti-6Al-4V alloy with the presence of oxygen. The role of the electronic subsystem in the development of the strain-induced phase transformations was discussed. [ABSTRACT FROM AUTHOR]

• Speciation profiles of NH 3 oxidation were obtained at elevated pressures. • Effects of different promoters (H 2 and CH 4) on oxidation of NH 3 were investigated. • Ab-initio calculations were performed to investigate reaction kinetics of NH 3. • An updated kinetic model was proposed and validated for numerical simulation. • Performances of different kinetic models in literature were investigated. Achieving carbon neutrality in ammonia production is feasible through the utilization of green hydrogen generated via water electrolysis using renewable electricity, alongside nitrogen extracted from the air. Ammonia, as an important hydrogen carrier, has attracted increasing attention among researchers as a prospective zero-carbon fuel. However, to enable its utilization in engines, further investigation into the reaction kinetics of ammonia, particularly its co-combustion with other promoters due to ammonia's inherently low reactivity, is imperative, especially under engine-relevant conditions. In this study, oxidation experiments involving pure ammonia, ammonia/hydrogen, and ammonia/methane were conducted within a variable pressure laminar flow reactor. The temperature range spanned 700–1000 K, with pressures ranging between 10 and 30 bar. Experiments were conducted under very lean conditions (0.02 for pure ammonia experiments and 0.05 for ammonia/hydrogen and ammonia/methane experiments), considering nitrogen, water, and carbon dioxide as final products. The mole fractions of N H 3 , H 2 , C H 4 , O 2 , NO, N O 2 , N 2 O , CO and C O 2 were measured using online continuous gas analyzers and GCs. Furthermore, the rate constants of various H-abstraction reactions in the ammonia sub-model were revised based on ab-initio calculations. An updated kinetic model, demonstrating satisfactory predictive performance concerning the oxidation properties of ammonia under elevated pressures, has been proposed. This model is developed based on data from the present work and that taken from other literature. Noteworthy phenomena related to ammonia oxidation were observed in this investigation. Additionally, further experimental and kinetic studies under engine-relevant conditions are advocated to facilitate the development and validation of accurate kinetic models under these conditions. [ABSTRACT FROM AUTHOR]

In this paper, the electronic properties of CdTe (100) films without impurities and with the addition of O2 molecules were investigated based on calculations from first principles. It was found that when the oxygen concentration increases from 8 to 14 %, the O2 molecule passes the energy barrier more easily, which indicates an increase in the catalytic activity of the CdTe film. Since oxygen affects the catalytic process, we recorded the movement of the band gap depending on the oxygen concentration. According to the calculated results of the study of small diatomic and triatomic clusters (Te, Cd), we found that the inclusion of oxygen atoms or atoms of other kinds in small clusters (Te, Cd) affects the catalytic activity of the studied systems as a whole. [ABSTRACT FROM AUTHOR]

The electronic, magnetic, optical and transport properties of ZnFe2O4 compound are calculated using the density functional theory implemented on Wien2k code with GGA + U approximation. The results obtained are in good agreement with the experimental results. In the visible range, ZnFe2O4 has a coefficient of absorption over 104/cm. The first and main critical point calculated with GGA + U appears at 2.10 eV, which is known as optical absorption edge. In addition, the X-ray Magnetic Circular Dichroic (XMCD) spectra exhibit two peaks in L3 edge revealing the existence of Fe3+ and Fe2+ ions, occupying the octahedral sites. Finally, using XMCD and XAS methods, we can calculate the spin and orbital moments of bulk spinel ferrite ZnFe2O4 compound. [ABSTRACT FROM AUTHOR]

We present a theoretical study of the magnetic properties for the pyrochlore-like NaCu 3 F 7 compound, which surprisingly experience little or no frustration. The magnetic effective exchange interactions were calculated using ab-initio methods explicitly treating the electronic correlation. A model Hamiltonian (quantum Heisenberg Hamiltonian, and for comparison a spin 1/2 Ising Hamiltonian) was built from these interactions and used to determine the zero temperature magnetic order versus magnetic field. The magnetic order at zero magnetic field is non frustrated and associated with the propagation vectorq→=(0,0,0). The magnetization versus magnetic field reveals the existence of a 1/3 plateau that could be observed in high-pulsed magnetic field experiments. Analyzing the magnetic interactions, we highlight the importance of the magnetic ion nature, and the lattice distortion, in the non-frustrated nature of the NaCu 3 F 7 magnetic structure, despite its triangular/Kagome subnetworks. We believe that this non-frustrated behavior could also take place in other triangular copper-based systems., (© 2024 IOP Publishing Ltd.)

Experimental and theoretical studies enabled the reveal of patterns of the microstructure formation in the surface layer of Ti-6Al-4V titanium alloy subjected to ultrasonic impact treatment. The mixed amorphous and nanocrystalline structure of the 200 nm thick uppermost surface layer of titanium dioxide TiO2 was demonstrated using transmission electron microscopy. The 5 µm thick intermediate layer containing nanocrystalline α grains, and the 50–60 µm thick lower layer containing fragmented α-Ti grains with retained β phase were also observed. The refinement of the β-Ti phase during ultrasonic impact treatment was accompanied by the formation of the orthorhombic (α″) martensitic phase. Molecular dynamics simulation of strains of a vanadium-doped titanium crystallite subjected to ultrasonic impact treatment revealed the formation of striped dislocation substructures as well as the development of reversible β→α phase transformations. Ab initio calculations of the atomic structure of V-doped Ti crystallites containing α, β or α″ phases of titanium were carried out. On the basis of the results of the experimental observations, a molecular dynamics simulation and ab initio calculations a mechanism was proposed, which associated the development of the strain-induced β→α″ phase transformations in Ti-6Al-4V alloy with the presence of oxygen. The role of the electronic subsystem in the development of the strain-induced phase transformations was discussed.

We developed a quantum-chemical approach for ab initio calculations of metastable-induced electron-emission spectra (MIES). In contrast to earlier work, our calculation method accounts for the anisotropy of the MIES spectra with respect to not only the direction of incidence of metastable helium but also to that of electron detection. Since we can freely choose both, incidence and detection direction in our simulation, our method is able to reconstruct MIES spectra which are dominated by Auger deexcitation for any experimental setups and orientation of the studied molecules. Here, we study the dependence of the MIES spectrum on the incidence and detection direction and other experimental parameters and compare the results for the case of adsorbed benzene with experimental data. [ABSTRACT FROM AUTHOR]

5-Hydroxytryptamine (5-HT; serotonin) regulates metabolism and various homeostatic mechanisms in the body, and is involved in depression. These complicated functions of 5-HT are supported by several 5-HT receptor and 5-HT transporter subtypes. The development of agonists/antagonists and activators/inhibitors of 5-HT receptors and transporters is a strong target for drug studies. Toward this purpose, we calculated the conformations and electrical states of ionized 5-HT in aqueous solution using ab-initio methods. When we assumed an ionized 5-HT molecule and three surrounding water molecules, the hydrogen bond network for these four molecules formed a ring shape, resulting in deformation of the pyrrole ring in the indole group of 5-HT. To our knowledge, this is the first finding demonstrating deformation of the indole skeleton. The findings suggest that the direct involvement of water in the binding between 5-HT and its receptors and transporters should be taken account when designing candidate 5-HT active compounds.

Beryllium silicate, recognized as the mineral phenakite (Be 2 SiO 4 ), is a prevalent constituent in Earth's upper mantle. This study employs density-functional theory (DFT) calculations to explore the structural, mechanical, dynamical, thermodynamic, and electronic characteristics of this compound under both ambient and high-pressure conditions. Under ideal conditions, the DFT calculations align closely with experimental findings, confirming the mechanical and dynamical stability of the crystalline structure. Phenakite is characterized as an indirect band gap insulator, possessing an estimated band gap of 7.83 eV. Remarkably, oxygen states make a substantial contribution to both the upper limit of the valence band and the lower limit of the conduction band. We delved into the thermodynamic properties of the compound, including coefficients of thermal expansion, free energy, entropy, heat capacity, and the Gruneisen parameter across different temperatures. Our findings suggest that Be 2 SiO 4 displays an isotropic behavior based on estimated anisotropic factors. Interestingly, our investigation revealed that, under pressure, the compression of phenakite is not significantly affected by bond angle bending., (© 2024 The Authors. ChemPhysChem published by Wiley-VCH GmbH.)

We present the ab - initio temperature and pressure dependent thermoelastic properties of body-centered cubic tungsten. The temperature dependent quasi-harmonic elastic constants (ECs) are computed at several reference volumes including both the phonon and the electronic excitations contribution to the free energy and interpolated at different temperatures and pressures. Good agreement with the experimental ECs on a single crystal at ambient pressure is found. The pressure and temperature dependence of the shear sound velocity measured on polycrystalline tungsten by Qi et al is also in agreement with theory. Some discrepancies are found instead for the compressional velocity at high temperature and this is attributed to the temperature derivative of the bulk modulus, higher in theory than in experiment. These conclusions are reached both by PBE and by PBEsol functionals. The two give elastic properties with a similar pressure and temperature dependence although the latter is closer to experiment at 0 K., (Creative Commons Attribution license.)

Based on the density functional theory and the Boltzmann transport theory, the thermoelectric properties of Mg 2 Si 1 - x Sn x solid solution with x = 0.25 , 0.5 and 075 were investigated. The calculated structural parameters were in good agreement with the previous work and the mechanical and dynamical stabilities were confirmed. The electronic band structure computed using the Tran-Blaha-modified Becke and Johnson (TB-mBJ) exchange potential indicated that the band gap can be tuned by the alloy effect. We combined first-principles calculations and the semiclassical Boltzmann transport theory by considering the electronic transport in the Mg 2 Si 1 - x Sn x solid solution to determine the effect of varying the Sn composition on the thermoelectric performance. Our results have shown exceptionally high electrical conductivity for Mg 2 Sn and higher Seebeck coefficient for Mg 2 Si . The highest figure of merit (ZT) was predicted for Mg 2 Si 1 - x Sn x solid solution with x = 0.5 where ZT has reached 0.55 with carrier concentration charge n = 10 20 cm - 3 (p-type doping) at intermediate temperatures. Consequently, the alloying system with p-type doping may improve the thermoelectric properties compared to the Mg 2 Si and Mg 2 Sn pristine compounds. [ABSTRACT FROM AUTHOR]

We have investigated the structural, elastic and thermodynamic properties of CaX (X = S, Se, and Te) using first-principles calculations. The exchange-correlation functional employed is the generalized gradient approximation of Wu and Cohen (GGA-WC). The estimated structural properties of these compounds are in excellent agreement with experimental data. The stability of the compounds was discussed on basis of the calculated elastic constants Cij, which are in good agreement with the experimental results. The thermodynamic properties of CaX materials are also calculated. Furthermore, the effects of temperature and pressure upon the heat capacities, expansion coefficients and bulk modulus have been calculated and discussed. [ABSTRACT FROM AUTHOR]

This paper studies the elastic, structural, electronic, magnetic, and topological properties of the η-Fe 2 C carbide under pressure by resorting to DFT-GGA's first principle via FPLAPW-WIEN2K and ElaStic1.0 software. Properties were calculated for strain vectors and pressures shown to maintain the orthorhombic structure of the carbide. Electronic bands, Fermi surfaces, and electron states are slightly distorted in the direction of the strain vector considered. The density of states, dominated by the 3d electrons of Fe, and to a lesser extent, by the 2p electrons of C, is lower in the pressure-borne compressed state than in the expanded one, a degree of hybridization existing between these states in certain energy regions, in tandem with a more extended first Brillouin zone and a higher Fermi level, which translates into greater structural stability in the latter state. The resulting magnetic anisotropy is a consequence of the difference in density of states between the spin-up and spin-down configurations, mainly in the orbitals of the aforesaid electrons. The pressure was also found to affect the number of bond, ring, and cage critical points (CP) found, as well as their distance from the atom. Graphic details of the calculation of properties in η-Fe 2 C Carbide. Unit cell. E vs V for different strains. Elastic modules. Electronic structure. DOS. 3-D map of electron charge density. Spin-up and spin-down Fermi surfaces. Image 1 • Properties were calculated for strain vectors and pressures shown to maintain the orthorhombic structure of the carbide, a structural transition being likely depending on the deformation and the pressure applied. The elastic stability and the ductile character of this carbide are confirmed. • The only change of the Fermi level by pressure affects the electronic details of the material in such a way that the density of states (DOS) is modified, thus generating greater electron occupancy for the expanded structure, with direct effects on both the electronic bands and the Fermi surface. • The density of states is lower in the compressed state than in the expanded one, in tandem with a higher Fermi level value, which translates into greater structural stability in the latter. The density of states is dominated by the 3d electrons of Fe, and to a lesser extent, by the 2p electrons of C. • Topologically, critical points (CP), to wit: bonds, rings and cages are found, the pressure affecting the atom-CP distance and the number of said points. • The magnetic anisotropy is a consequence of the difference in density of states between the spin-up and spin-down configurations, mainly in the 3d and 2p orbitals of Fe and C, respectively. • The effect of the pressure on the transition from a compressed to an expanded structure not only decreases the magnetic moment of the carbon and on the interstices, but also increases the magnetic moment of the Fe, which bears a higher magnetic moment in the cell, while the charge in the cell decreases slightly due to the reduced charge in the interstice. [ABSTRACT FROM AUTHOR]

In this paper, we used the ab-initio calculations, based on the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), to simulate the magnetic properties of ZnO, doped and co-doped with manganese and carbon, respectively. For this purpose, we have used two different approximations: the Local Density Approximation (LDA) and the Local Density Approximation-Self-Interaction Correction (LDA-SIC). Numerical results are presented for the compound Zn1 − 0.06Mn0.06O1−xCx when doping and co-doping is performed with Mn and C as doping elements. Total and partial DOSs are given for different concentrations using the two approximations, LDA and LDA-SIC. It is found that for 6% with doping by Mn the system becomes magnetic. The co-doping with carbon changes the behavior of the system : it becomes also magnetic for 4, 6 and 10% concentrations within both, LDA and LDA-SIC approximations. Furthermore, we have discussed the type of mechanism of exchange interaction and found that the double exchange is responsible for the appearing magnetism in the system, within the LDA and p-d interaction for LDA-SIC approximation. For 10% of carbon, we have found that the critical temperature approaches 280 K in the LDA approximation solely; and is about 305 K in the LDA-SIC approximation. [ABSTRACT FROM AUTHOR]

Thermodynamic data for crystalline white and grey tin were assessed using an extended Einstein model from 0 K. Ab-initio simulations in the framework of density functional theory (DFT) with the quasiharmonic approximation (QHA) were carried out to define the heat capacities for both phases of tin from 0 K up to room temperatures. Good agreement was observed between theoretical and experimental heat capacities, which makes it possible to combine theoretical and experimental data to determine the standard entropies. Data for the liquid phase were described using a two state model. During the assessment, careful analysis of the experimental data was carried out. In order to fulfil the need for a precise evaluation of S o 298 we needed to use an additional technique using multiple Einstein functions, which allows the experimental heat capacity and enthalpy data for the solid phase to be approximated accurately from 0 K up to the melting point and to estimate solid phase transition entropy and enthalpy which are difficult to measure due to a high activation barrier. Additional measurements of heat capacity were carried out where existing data were scarce. • Thermodynamic data for α and β Sn were assessed from 0 K. • Cp of β-Sn were measured in the temperature interval 80–372 K. • Ab-initio simulations to define the Cp for α and β Sn were carried out. • Multiple Einstein functions were used for a precise evaluation of S o 298. • Two-state model was used for the liquid phase. [ABSTRACT FROM AUTHOR]

The electronic, mechanical, and optical properties of the Kagome staircase compounds, Mn3V2O8 and Ni3V2O8, have been investigated using the VASP (Vienna ab-initio Simulation Program) that was developed within the density functional theory (DFT). The spin polarized generalized gradient approximation has been used for modeling exchange-correlation effects. The electronic band structures for both compounds and total and partial density of states corresponding to these band structures have been calculated. Spin up (spin down) Eg values for Mn3V2O8 and Ni3V2O8 compounds are 0.77 eV indirect (3.18 direct) and 1.58 eV indirect (0.62 eV) direct, respectively. The band gaps of both compound is in the d-d character. Bulk modulus, shear modulus, Young's modulus, Poisson's ratio, anisotropic factors, sound velocity, and Debye temperature were calculated and interpreted. [ABSTRACT FROM AUTHOR]

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Abstract We investigated the electrical properties and electronic structure of defect-containing chalcopyrite AgIn 5 Te 8 and chalcopyrite AgInTe 2. We found p-type AgIn 5 Te 8 had worse electrical properties than AgInTe 2 , which is probably attribute to its lower mobility due to defects at its cation sites. Such defects would do the most to degrade its electrical properties because both compounds have similar valence band structure near the Fermi energy level. Conversely, n-type AgIn 5 Te 8 might be a better thermoelectric material than AgInTe 2 , if not for its lower mobility, because it has better band structure, with multiple electron pockets at the high symmetry points in its conduction band. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Structural, optoelectronic and thermoelectric properties of rare earth Zintls Ca 3 RESb 3 (RE = La, Ce and Pr) isostructural with anti-Th 4 P 3 are studied in cubic I 4 − 3d space groups. Structural parameters are reliable with experimental results and lattice parameters are decreasing due to lanthanide contraction from La to Pr. Cohesive energy and enthalpy indicate that Ca 3 PrSb 3 is more stable than the others. Electronic properties reveal the direct bandgap semiconductors character of these compounds at the central symmetry, these compounds are and are increases going from La to Pr. Based on their optical characteristics, all material are active in the infrared region. Because of their optical dynamic quality, they could be used in optoelectronic devices. Based on their thermoelectric characteristics, they are effective thermoelectric materials as thermoelectric generator. [ABSTRACT FROM AUTHOR]

Abstract Atomic structure evolution induced by thermal relaxation is investigated in Fe 80 P 11 C 9 metallic glass by a suite of techniques. The topological structure of Fe 80 P 11 C 9 metallic glasses characterized by the Voronoi polyhedrons varies with relaxation proceeding. Meanwhile, the results of partial pair distribution functions and local composition distribution indicate that the degree of the chemical order for different species changes and the solvent-solute correlation significantly enhances. Moreover, the Mössbauer spectra measurements suggest that significant element redistribution occurs during the structural relaxation. Hence, only topological structure change is insufficient to describe the structural relaxation. These results manifest that the structural relaxation can be described via heterogeneity degeneration, which is also supported by the small angle X-ray scattering measurements. Highlights • Synchrotron XRD and AIMD are used to study the relaxation process of a Fe-based metallic glass. • Enhancement of the solvent-solute correlation accompanied by the topological structure change occurs during relaxation. • Heterogeneity degenerates upon relaxation. [ABSTRACT FROM AUTHOR]

Abstract Nanotwinning exhibits strengthening effects in many metals, semiconductors, and ceramics. However, we show from ab - initio calculations that nanotwins significantly decrease the strength of thermoelectric semiconductor Mg 2 Si. The theoretical shear strength of nanotwinned Mg 2 Si is found to be 0.93 GPa, much lower than that (6.88 GPa) of flawless Mg 2 Si. Stretching the Mg Si bond under deformation leads to the structural softening and failure of flawless Mg 2 Si. While in nanotwinned Mg 2 Si, the Mg Si bond at the twin boundary (TB) is expanded to accommodate the structural misfit, weakening the TB rigidity and leading to the low ideal shear strength. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Abstract The three-dimensional (3D) growth pattern, preferred growth directions and the underlying growth mechanism of magnesium alloy dendrite are investigated via 3D experimental characterization and multiscale mathematical simulations. It is found that the formation of the dendritic microstructure is associated with the magnitude of surface energy anisotropy. The results based on synchrotron X-ray tomography and electroback scattered diffraction techniques show that typical 3D morphology of the α-Mg dendrite exhibits an 18-primary-branch pattern, with six along the < 11 2 ¯ 0 > basal direction, and the other twelve along the < 11 2 ¯ 3 > nonbasal direction. The underlying mechanism is investigated by performing relevant atomistic calculations at the ground state and the elevated temperatures in light of density functional theory (DFT) and quasi-harmonic approximation (QHA). The results indicate that the preferred growth direction for the α-Mg dendrite growth is < 11 2 ¯ x > rather than < 10 1 ¯ x > , and the anisotropic surface energy decreases as the temperature increases. Subsequent analysis further confirms that the preferred growth directions of the α-Mg dendrite at different temperatures correspond consistently to those orientations with higher surface energy anisotropy, i.e., the < 11 2 ¯ 0 > and < 11 2 ¯ 3 >. Accordingly, the 3D phase-field simulations are performed to investigate the growth behavior of the α-Mg dendrite, with the anisotropic strength determining via DFT-based calculations. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract High-pressure X-ray diffraction studies on MgCu 2 type phase of UOs 2 have been carried out up to 36 GPa. The compound remains in its parent phase up to 12 GPa with bulk modulus 261 GPa. Beyond 12 GPa, a first order phase transformation is observed. The phase transition is sluggish in nature and completes at 20.1 GPa. The high-pressure phase is found to be a hexagonal cell with lattice parameters a = 3.013 Å and c = 4.267 Å. Charge density calculations show that uranium tetrahedra in the lattice are responsible for the phase transition. The density of state plots at Fermi level, wherein a pseudogap originates at high pressures, confirms the existence of a high pressure phase and uranium site is found to contribute significantly to such changes in density of state. The retrievable high pressure phase is found to be the least compressible among uranium intermetallic compounds with bulk modulus of 366 GPa. [ABSTRACT FROM AUTHOR]

Abstract We study from first principles the stability of neutral and charged oxygen vacancies in lutetium oxyorthosilicate, Lu 2 SiO 5 , as well as its possible modification due to the presence of Ce 3 + , as present in commercial scintillators. We show that the neutral oxygen vacancy with the lowest formation energy forms at the oxygen sites within the [SiO 4 ] tetrahedra instead of the interstitial oxygen site bonded exclusively to lutetium atoms. The discrepancy with a previous study is attributed to the quality of the pseudopotential. Support for these results is found by performing a bonding analysis of the oxygen sites, as well as oxygen vacancy calculations in the iso-structural Y 2 SiO 5 compound. In addition, we find that the incorporation of Ce 3 + ion does not affect the stability of oxygen vacancies in Lu 2 SiO 5. [ABSTRACT FROM AUTHOR]

Structural and electronic properties of bulk Cu 3 N and monolayer Cu 2 N under ab -plane strain have been evaluated from first principles. Furthermore, the electronic structure of a layered AgCu 2 N system was studied. Structural optimizations were performed within the GGA approach, and band structures were obtained with the modified Becke-Johnson (MBJLDA) exchange-correlation potential. Compressive strain leads to a decrease of a band gap in the Cu 3 N parent compound and Cu 2 N atomic sheet, whereas tensile strain causes an opposite effect on band structures of these systems. Furthermore, some transitions between direct and indirect band gaps, induced by tensile strain, are revealed in these materials. The monolayer Cu 2 N is found semimetallic. The hypothetical AgCu 2 N compound is predicted to be a semiconductor with the degenerate indirect R - Γ and R - M gaps, which are close in value to the direct R - R gap. The findings presented here suggest that tensile strain and a doping with Ag atoms are promising tools for band gap engineering in Cu 3 N-based materials, thin films and heterostructures in particular. [ABSTRACT FROM AUTHOR]

Oxygen isotope fractionation between carbonate minerals and water is used as an environmental proxy to estimate mineral formation temperatures or isotopic composition of precipitating fluids. To date no experimental data on the oxygen isotope fractionation factor between smithsonite (ZnCO 3 ) and water, α( 18 O) smithsonite-water  = ( 18 O/ 16 O) smithsonite  / ( 18 O/ 16 O) water , exist. Therefore, in the present study experimental work on smithsonite synthesis in the temperature range between 25 and 80 °C is coupled with ab-initio based theoretical calculations. Laboratory precipitation experiments took place in titanium reactors at elevated pCO 2 (~10 atm) in order to induce the formation of smithsonite from hydrozincite (Zn 5 (CO 3 ) 2 (OH) 6 ), which is the precursor phase initially formed at 25 °C and low pCO 2 (pH ~ 6.8). The constant α( 18 O) smithsonite-water  = (1000 + δ 18 O smithonite ) / (1000 + δ 18 O water ) value reached at a reaction time ≥ 10,000 min (7 days) suggests near equilibrium conditions. Based on the experimentally obtained temperature relation of α( 18 O) smithsonite-water at 25, 40, 60, and 80 °C the integrated equation can be linearly described by the function: 10 3 lnα 18 O smithsonite − water = 2.79 ∗ 10 6 / T 2 – 0.95 ± 0.06 ∗ 10 6 / T 2 + 0.60 where the temperature is in Kelvin. The ab initio calculations suggest that this relation can be described in the temperature range from 0 to 100 °C as: 10 3 lnα smithsonite − liquid water = 3.21 ∗ 10 6 / T 2 – 3.63 ± 0.025 ∗ 10 6 / T 2 + 0.90 The α( 18 O) smithsonite-water values from the experimental approach fit within error to the theoretical relationship from the literature and the above ab initio calculations. Difference in slope between the experiment and theoretical obtained equation likely reflects modeling inaccuracies, whereas kinetic effects cannot be completely ruled out in the experimental approach. The obtained α( 18 O) smithsonite-water values match with the general sequence of Zn 2+  < Fe 2+  < Mn 2+  < Ca 2+ for mono-cation trigonal Me-carbonate minerals suggesting incorporation of lighter oxygen isotopes in the carbonate mineral at increasing cation radius as indicated from thermodynamic considerations. Potential applications of oxygen isotope fractionation during smithsonite formation for natural aqueous surroundings are discussed. [ABSTRACT FROM AUTHOR]

We have fabricated a pseudo single crystal of cementite under a rotating magnetic field and investigated its easy and hard axes of magnetization, and determined its magnetocrystalline anisotropy energy. The obtained results are as follows: the hard and easy axes of cementite are the a- and c -axes of the orthorhombic structure with the space group Pnma , respectively. The hard axis observed experimentally was in good agreement with that obtained by an ab initio calculation; however, such consistency was not observed for the easy axis. The magnetocrystalline anisotropy energy was determined as 334 ± 20 kJ/m 3 at 5 K. [ABSTRACT FROM AUTHOR]

Density functional theory (DFT) and coupled-cluster (CCSD(T)) theory have been applied to investigate the geometric, growth pattern, bonding, stability, dissociation, adsorption and electronic properties of arsenide doped boron clusters B n As (n = 1–9). Vertical ionization potential (VIP), vertical electron affinity (VEA), HOMO-LUMO energy gap ( E g ), binding energy ( E b ), chemical hardness ( η ), and radial distribution functions (RDFs) of B-As and B-B interactions have also been investigated and discussed for the most stable isomers. The results show that the As-dopant atom prefers to locate in peripheral regions for the studied sizes. Arsenic atom can obviously enhance the stability of B n As clusters. [ABSTRACT FROM AUTHOR]

In the present study, the formation mechanism of tearing topography surface (TTS), which is observed after slow strain-rate tensile tests of H-charged pearlitic specimens, was investigated in detail. The TTS always appeared at the subsurface of failed H-charged specimens, where H atoms were concentrated after room-temperature electrochemical H-charging. The TTS consisted of stepped flat surfaces and dimpled surfaces. The flat surface was caused by the coalescence of sharp micro-shear cracks, not micro-voids, of H-enriched cementite (θ) platelets in a pearlite colony, namely brittle transcolonial fracture. The regions surrounding the flat surface were H-depleted due to the migration of H atoms into neighboring micro-shear cracks during tensile deformation. As a result, the H-depleted regions were fractured by the typical coalescence of micro-voids, namely relatively ductile shear cracking, resulting in dimpled surfaces after tensile fracture. These results mean that the TTS region, strictly speaking, the flat surface region, which is generated by transcolonial fracture inside the TTS region, is an initial site of H-induced cracking of pearlitic steel. The ab-initio calculations of the energy value of H desorption from a C vacancy in θ supported the recent report that H atoms are concentrated inside the θ platelets after H charging. [Display omitted] [ABSTRACT FROM AUTHOR]

Using the first-principles calculations within the Korringa-Kohn-Rostoker (KKR) method combined with the coherent potential approximation (CPA), the structural, optical and magnetic properties of rare-earth nitride HoTMN doped with transition metal (TM) atoms (Ti, V, Cr, Mn, Co and Ni) are investigated as a function the generalized gradient approximation and self-interaction correction (GGA-SIC) approximation. The optical properties are studied in detail by using ab-initio calculations. Using GGA-SIC we have showed that the bandgap value is in good agreement with the experimental value. Using GGA-SIC approximation for HoN, we have obtained a bandgap of 0.9 eV. Some of the dilute magnetic semiconductors (DMS) like HoTMN under study exhibit a half-metallic behavior, which makes them suitable for spintronic applications. Moreover, the optical absorption spectra confirm the ferromagnetic stability based on the charge state of magnetic impurities. [ABSTRACT FROM AUTHOR]

The structural and electronic properties of wurtzite Tl x In 1− x N materials have been investigated from first principles within the density functional theory (DFT). Band structures were obtained with the modified Becke-Johnson (MBJLDA) approach. A narrow band gap of 63 meV, induced by a strong spin-orbit coupling, is predicted in the hypothetical thallium nitride. The band gap inversion in TlN suggests that this compound is a promising candidate for a topological insulator. The lattice parameters of Tl x In 1− x N alloys exhibit a linear behavior as a function of a Tl content x . An incorporation of Tl atoms in these systems leads also to a linear decrease of a band gap. For x > 0.3 a very narrow energy gap, analogous to that of the pure TlN, is revealed. The band gap reduction of 26 meV/%Tl is comparable in value to those reported in the literature for dilute Bi-doped GaSb and InSb. The Tl-doped InN systems are promising materials for infrared optoelectronic devices. [ABSTRACT FROM AUTHOR]