Principles Calculations Research Articles

Investigating magnetic properties and Curie temperatures of FeX2 (X=S, Se, Te) monolayers

In recent years, there has been a growing interest in two-dimensional magnetic materials. With their unique properties and tunable characteristics, magnetic monolayers hold significant potential for the next-generation devices. This study employs the first principles calculations to examine the electronic, structural, and magnetic properties of the hexagonal and trigonal FeX2 (X=S, Se, Te) monolayers. The calculations show that only two configurations are dynamically stable which are hexagonal FeS2 and FeTe2. Both H-FeS2 and H-FeTe2 monolayers exhibit metallic behavior in PBE calculations. Furthermore, the results indicate that these monolayers also exhibit ferromagnetic behavior. This ferromagnetic ordering suggests significant interactions between the magnetic moments. The magnetic exchange constants are determined by using 2D Ising model. After determining the magnetic exchange constants, a Monte Carlo simulation is performed to obtain the Curie temperature. Furthermore, the influence of the Hubbard U parameter on the electronic and magnetic structure was also examined, revealing significant modifications in the band structure and magnetic moments. Additionally, magnetic exchange constants were calculated for the PBE+U case, as well as using the TB2J method, to provide a comprehensive understanding of the magnetic properties of the stable structures.

Adsorption behavior of Cl2 on TiC0.89O0.11(001) surface based on the first principle calculation

Based on the first-principles ab initio calculation method of density functional theory (DFT), the adsorption models of Cl2 molecules on both the TiC0.89O0.11(001) intact surface and the carbon vacancy surface were established, followed by calculations and analysis of the adsorption structures, adsorption energy, differential charge density, and density of states (DOS). The results demonstrate that the adsorption process of Cl2 molecules on the TiC0.89O0.11(001) surface involves chemical adsorption, with a higher likelihood of dissociation into Cl atoms during adsorption. These dissociated Cl atoms can potentially interact with surface Ti and/or C atoms to form Ti-Cl bonds, C-Cl bonds, Ti-Cl-C bonds, and Ti-Cl-Ti bonds. Simultaneously, the stability of the adsorbed structure is influenced by both the bonding conditions between Cl atoms and surface atoms and the position of Cl atom adsorption (e.g., whether it is located above the vacancy C). Following adsorption, there is a weakening in the bonding strength of Ti-C or Ti-O bonds on the TiC0.89O0.11(001) surface. During the adsorption process, Cl atoms can either act as electron donors or acceptors. When the Ti-Cl bond structure is formed, Cl atoms function as electron acceptors; however, when the C-Cl bond structure is established, Cl atoms predominantly act as electron donors. Surface Ti atoms act as electron donors while surface C and O atoms function as electron acceptors. Additionally, the presence of surface carbon vacancy enhances the interaction between Cl and Ti atoms, weakens the interaction between Cl and C atoms, and attenuates the interaction between C, O, and Ti atoms in the structure. And it can augment the electron acquisition by Cl2 molecules upon adsorption, reduce the adsorption energy, and promote greater stability in the adsorption structure. All the effects contribute to facilitating TiCl4 formation.

Study of native point defects in Al0.5Ga0.5N by first principles calculations

To explore the formation mechanism of native point defects in high Al content AlGaN film, the first principles methods are applied to study the native point defects in Al0.5Ga0.5N. The different kinds of vacancies, interstitials, and antisites are investigated. The formation energies of Al0.5Ga0.5N with native point defects under different charge states and growth conditions are analyzed and compared. Then, the preferable charge state, donor and acceptor properties of Al0.5Ga0.5N with different native point defects are explicitly obtained. The results show that AlN, GaN, Ali, and VN exhibit donor properties in p-type condition while VGa, VAl, VN, and NGa exhibit acceptor properties and can play roles as compensating center in n-type Al0.5Ga0.5N under metal rich condition. For N rich condition,VGa, VAl, NGa, and NAl are favorable acceptors in n-type Al0.5Ga0.5N. Meanwhile, the charge distribution and bonding state of Al0.5Ga0.5N with native point defects are explored. It is found the N atoms in Ni and NGa form covalent bond and ionic bond with atoms in Al0.5Ga0.5N. Moreover, the band calculation reveals that the removal of N atom in Al0.5Ga0.5N makes the conduction band fatter and the effective masses of electrons increase while the introduction of N point defects make the valence band flatter, increasing the effective masses of holes. Furthermore, the corresponding thermodynamic transition energy levels of defects under different charge states are summarized. It is found that the thermodynamic transitions for VN, Ni, and NAl may likely to happen under certain conditions. The above studies yield a detailed and quantitative description of native point defects in Al0.5Ga0.5N, which helps to get a deeper insight to the growth and doping of AlGaN.

Synthesis, structure, spectra, NLO behavior, and in-silico study on anti-tumor and anti-tuberculosis efficacy of (Z)-3-((Z)-3-phenylallylidene)benzo[4,5]imidazo[1,2-c]thiazole-1(3H)-thione

In this study, we report the synthesis of (Z)-3-((Z)-3-phenylallylidene)benzo[4,5]imidazo[1,2-c]thiazole-1(3H)-thione (ThBMT). This compound belongs to an important group of molecules containing two or more heterocyclic moieties. ThBMT was experimentally characterized using IR and NMR spectroscopy. The absolute 3D structure of ThBMT was determined by single-crystal X-ray diffraction, revealing crystallization in the monoclinic space group P21/c with four molecules in the unit cell. First principle theoretical calculations were carried out via the Density Functional Theory (DFT) method with B3LYP and B3LYP-GD3(BJ) functionals using the 6–311++G(d, p) basis set. The geometrical parameters of ThBMT were analyzed and compared to those of optimization, which were found to be consistent. The crystal packing and their intermolecular interactions were studied by Hirshfeld surface analysis, revealing that the most common interactions were C-H⋅⋅⋅N and C-H⋅⋅⋅S. Furthermore, theoretical vibrational wavenumbers were computed, assigned, and compared to the experimental ones. The (1H, 13C) NMR chemical shifts were calculated and compared with experimental values. The compound's nonlinear optical (NLO) properties were also investigated to understand its potential applications in optoelectronics, and compared to those of the benzimidazole fragment. The results showed promising NLO characteristics. Molecular docking and in silico ADMET studies were reported to highlight the biological behavior of ThBMT, indicating anti-tuberculosis properties, and anti-tumor activities against HeLa and HepG2 cancer cell lines.

Rational design of 2D blue phosphorene/Ti2BT2 (T=Se, Te) heterostructures as high-performance anode materials for alkali-metal ion batteries: A first principles study

Blue phosphorene (BlueP) is extensively regarded as an attractive anode for the next generation of metal-ion batteries (MIBs) owing to the rapid ion diffusion and high storage capacity; however, its electrochemical performance is still seriously impeded by the intrinsically low conductivity and poor mechanical stiffness. To overcome the above obstacles, we theoretically designed BlueP/Ti2BSe2 and BlueP/Ti2BTe2 heterostructures, and explored their potential as the anodes of MIBs using first principles calculations. The computational results demonstrate that the resulting heterostructures have excellent thermal and mechanical stability. Moreover, the designed two heterostructures show low ion diffusion barrier (<0.30 eV) with inherent metallicity, which greatly contributes to the rate performance of MIBs. Remarkably, the BlueP/Ti2BSe2 (BlueP/Ti2BTe2) anode delivers high Li/Na/K storage capacities of 492.68 (379.54)/410.54 (379.54)/191.59 mA h/g, and suitable averaged open circuit voltages (OCVs) of 0.56 (0.33)/0.33 (0.10)/0.42 V. This work not only broadens the BlueP-based 2D heterostructures, but also lays a solid foundation for the theoretical design of exceptional anodes.

Chitosan-derived N-doped porous carbon with fiber network structure for advanced lithium‑sulfur batteries

The flexible design and construction of advanced carbon-based sulfur hosts contribute to the rapid redox and reaction kinetics of lithium polysulfides (LiPSs) in lithium‑sulfur batteries (LSBs), laying the foundation for the next generation of high-energy density energy storage devices. Herein, chitosan (CS)-derived porous N-doped carbon with fiber network structure was prepared by a simple freeze-drying method combined with sintering process. The effect of inorganic salt additives on the morphology of CS-derived carbon was investigated by SEM. The types and contents of N-doping were investigated through XPS analysis. The influence of morphology and N content on the performance of LSBs has been explored in detail through cycling and CV testing. In addition, the true active sites in the CS-derived carbon were determined by XPS and first principles calculations. As an active species, pyrrolic N exhibits superior adsorption energy and the most suitable degradation energy barrier for LiPSs. As the optimal electrode, the performance of LSBs under different electrolyte to sulfur (E/S) conditions was further investigated to explore the potential application of CS-KOH electrodes in high-energy density batteries. The results unveil that the influence of E/S on Li2S deposition is quite significant, with a limit of 5 μL mg−1. This work provides a new strategy for the preparation of high-performance advanced carbon-based materials with fiber network structures from polysaccharide biomass, and also promotes the application of CS in energy storage.

Unveiling thermally driven photoluminescence in CVD grown MoS[formula omitted] dendritic flake

High-quality MoS2 nanostructures were fabricated via chemical vapor deposition technique on SiO2/Si substrate. In this paper, the effect of temperature on the photoluminescence behavior of MoS2 dendritic flake is addressed. We scrutinized the photoluminescence spectra of monolayer and multilayer regions of MoS2 in the temperature range 300 K–680 K. Monolayer and multilayer behavior of MoS2 flakes are confirmed by Raman and Photoluminescence spectroscopy. The excitonic peaks from the multilayer regime become less intense and show a red shift compared to the monolayer PL spectra. Thermally-induced bandgap modulation of MoS2 is demonstrated. The excitonic intensity and peak positions reveal pronounced temperature-dependent changes. These changes are explicable through the increased electron–phonon interaction and lattice rearrangements. Furthermore, first principle calculations are employed to glean insight into the impact of atomic rearrangements on the band gap behavior of MoS2. Our research presents a detailed understanding of thermally driven band gap modulation of monolayer and multilayer MoS2, which is essential for designing optoelectronic devices.

Mechanical strain effect on the optoelectronic properties and photocatalysis applications of layered AlN/GaN nanoheterostructure.

The aim of this work is to use first principles calculations to examine the effects of different mechanical strains on the optoelectronic and photocatalytic capabilities of the 2D/2D nanoheterostructure of AlN/GaN. By utilizing the lmBJ (Meta-GGA) and PBEsol (GGA) functional, the bandgap of the nanoheterostructure is calculated and found to be 4.89eV and 3.24eV. Simulated 2D AlN/GaN nanoheterostructure exhibits exceptional optical and electronic characteristics under applied biaxial tensile and compressive strains. The band gap changes from 4.89 to 3.77eV, while the energy gap nature transitions from direct to indirect during tensile strain fluctuations of 0% to 8%. Strain is also found to have a significant effect on the optical absorption peaks. And a 0-8% rise in tensile strain causes the initial absorption peak of the 2D AlN/GaN nanoheterostructure to shift from 4.88 to 4.20eV, which results in a 14% red shift in photon energy for every 2% change in strain. Furthermore, the optimum bandgap and band edge positions of the 2D AlN/GaN nanoheterostructure enable the water redox process to produce hydrogen and oxygen for wide range of pH. Thus, modification via strain may be an effective method for altering the optical as well as electronic characteristics of a 2D AlN/GaN nanoheterostructure, and this study may pave the way for new applications of this material in optoelectronic devices in the future. In the current work, density functional theory is used to explore every attribute of the 2D AlN/GaN nanoheterostructure. To characterize the electronic exchange-correlation, we used the PBEsol functional. In order to prevent any interlayer contact between periodicity of images, a vacuum is produced along the z-direction of approximately 10 Å. To increase the precision of bandgap prediction, the electronic and optical characteristics were computed using the meta-GGA lmBJ functional. To account for interlayer van der Waals interactions, nanoheterostructure computations were performed using the DFT-D3 functional.

Study on interface characteristics of WC-Co doped Y rare earth element cemented carbide cutting tool and its influence on material properties

The influence of doping rare earth element Y on the material properties at the W and C interfaces of WC (0001)/Co (111) was studied using first principles calculations, taking into account adhesion work, interface energy, density of states, and Mulliken population. The grain size of WC-Co cemented carbide doped with rare earth element Y was analyzed before and after doping through cellular automata simulation. The microscopic morphology of the cemented carbide materials before and after doping with Y element was observed and analyzed by experiments, and their mechanical properties were tested. The research results have shown that the interface structure doped with Y has smaller interface energy, greater adhesion work, and stronger interface bonding ability. All four interface models exhibit metallic properties, and the addition of Y element enhancing the metallicity of WC-Co. The W-d and Y-p orbitals undergo orbital hybridization and generate covalent bonds, improving the durability and bonding strength of the material. The bond length of C-W at the interface after doping is smaller than that before doping, and the population is greater than that before doping, indicating an enhanced stability of the interface. After the addition of rare earth element Y, the crystals underwent through-crystal fracture, and the fracture showed irregular shapes, which improved the bonding strength of the interface. Through the cellular automata simulation, it was found that the grain size after doping with Y element was significantly smaller than that before doping, and it was experimentally verified that the doping of rare earth element Y played the role of grain refinement. At the same time, it could reduce the coefficient of friction of the material, and improve the overall performance of the cemented carbide material.

Vanadium Oxides in Neuromorphic Computing: Unveiling Insights through First Principles Calculations

Neuromorphic computing represents a revolutionary approach to developing analog non-volatile memory (NVM) devices. This technology relies on electron-correlated materials capable of replicating the functioning of synapses and neurons in the brain, making it ideal for energy-efficient parallel computing applications. Among the myriad of innovative materials suitable for neuromorphic computing, such as conductive polymers, organic semiconductors, and nanowires, among others, electron-correlated transition metal oxides stand out for their ability to undergo metal-insulator transitions either by tuning their oxygen content or the stoichiometry of an intercalating metal ion. In this talk we discuss from a first principles perspective the pivotal role that vanadium oxide has the potential to play in the development neuromorphic computing devices. First, we examine the use of vanadium oxide as a Mott insulator capable of undergoing a stable phase separation process that is suitable for non-volatile electrochemically activated random access memory devices (ECRAM). A stable phase coexistence across multiple segregated vanadium oxides states provides the device the ability express non-volatile memory behavior after precise tunning of oxygen vacancies into VO2. The correlation between these oxides’ formation energies and their oxygen content provides clues on the stable formation of coexisting crystalline phases that provide tunable resistivity based on the relative fraction and distribution of each phase with unusual retention, with an estimated 1% loss over 14 years in ambient conditions. Second, we address the structural and electrical properties of β’-CuxV2O5 based on temperature and Cu content. Ab-initio molecular dynamics calculations provide a close-up view of the correlation between Cu content and mobility and its ability to induce structural distortions to the intercalating β’-CuxV2O5 host that spike close to the insulator-metal transition (IMT).

Study of Electronic and Optical Properties of Low-Dimensional Nanosystems by First Principles Calculations

The development of new techniques for material manipulation at the nanoscale, as well as advanced numerical tools for material design, has opened up new prospects in the engineering of novel low-dimensional systems with properties specifically designed for applications in different fields, from photonics to energy conversion. Zero-, one-, and two-dimensional nanosystems show unique electronic, optical, and transport properties that can be tuned, for instance, by size reduction, passivation, and doping. In this talk, we discuss ab-initio results obtained in the study of structural, electronic, and optical properties of low-dimensional systems, in particular focusing on silicon, germanium, and silicon/germanium nanostructures. The analysis of mechanisms that can be exploited to tune Auger recombination and carrier multiplication processes, as well as of those that affect the formation of the band offset (Type I and Type II) at the nanoscale, will be discussed. At the end, effects induced by anion ordering on electronic and optical properties of metal oxynitrides will be analyzed.

(Invited) Solving the Energy Storage and Energy Conversion Conundrum – Materials to the Rescue

Energy storage systems have witnessed a meteoric rise ever since Sony commercialized the first Li-ion battery in 1994. Over the years, there have been a plethora of cathode, anode and electrolyte systems developed with stable cycle life and high coulombic efficiencies currently deployed in commercial electric vehicles. Similarly, alternate silicon and tin anodes were targeted as the next generation anodes to ubiquitous carbon. Recalcitrant volume expansion and ensuing solid electrolyte interphase (SEI) issues have reverted the focus back to the omnipresent high-energy density Li metal with efforts to overcome the ominous flammability and safety issues. Escalated impending demand for higher energy density have also made sulfur, an economic and common industrial effluent an attractive active material reverting attention back to Li-S batteries. Similarly, the portentous signs of global warming and the concomitant desire for developing green energy solutions have made hydrogen an imperative and attractive energy source providing the impetus for economic proton exchange membrane (PEM)-based water electrolysis (PEMWE) and fuel cells (PEMFCs). Like the energy storage field, PEMWE and PEMFCs have also witnessed intense research activity over the years following the early work on direct methanol fuel cells (DMFC). Developing high performance materials systems for energy storage and super responsive low-cost electrocatalysts still remain the major conundrum for developing high energy density and high-power density energy storage and conversion systems, respectively.This presentation will discuss the materials challenges that need to be overcome in Li-S batteries and PEM-based water electrolysis and fuel cells. Specifically, efforts aimed at achieving high-energy density cathodes and anodes as well as electrolyte additives for meeting the 500 Whkg-1 energy density targets for electric vehicle technology will be discussed. High sulfur (4-6 mg/cm2) loaded confined cathodes with unique ability to trap the pernicious polysulfide species combined with unique theoretical first principles calculations derived functional electrocatalysts exhibiting the propensity to reversibly catalyze the formation of Li2S and elemental S will be discussed. In tandem, progress made in generating new dendrite-free anodes and low-density current collectors exhibiting areal capacities as high as 15 mAh/cm2 with stable cycling over 100 cycles as well as electrolyte additives matching the cathode and anode performances will be outlined. Similarly, the journey into developing innovative low temperature chemical complexation approaches to novel bifunctional metallic nanostructured electrocatalysts first for DMFC systems and later how the unique approaches were modified targeting acid mediated PEMWE and PEMFCs comprising nanoscale metallic and complex ceramic doped oxide systems will be presented and discussed. Specifically, efforts made in the direction of realizing a unitized regeneration fuel cell (URFC) systems will be outlined and discussed in detail.

Computational insights into the structure and decomposition behaviors of 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide under high pressure up to 10 GPa.

Inspired by the recent successful synthesis of the energetic compound 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide (ICM-102), which displayed a good balance between high energy and sensitivity, the response of the structure and decomposition behaviors of ICM-102 to high pressure was systematically investigated using first principle calculations. ICM-102 exhibited a graphite-like layer structure, with the c-axis and the a-axis mainly contributing to the distance between the molecular planes. As the pressure increased from 1atm to 10 GPa, this distance decreased from 3.166 to 2.689 Ǻ. The hydrogen bonds had the most contribution to the non-covalent interactions within the same molecular planes, resulting in the b-axis discontinuity. However, van der Waals interactions gradually appeared between molecular planes as the pressure increased to 2.5 GPa. Based on the analysis of crystal orbitals, the distribution of π bonds and the Laplacian bond order (LBO), it was determined that the generation mechanism of H2O molecules involved the cleavage of N-Oc (coordinated oxygen atoms), followed by intermolecular hydrogen transfer reactions, and ultimately the formation of H2O molecules through competition with H atoms in the amino groups within the same molecules. More importantly, the pressure dependence of LBO values for N-Oc revealed that high pressure could inhibit the ICM-102 decomposition process due to reinforcing hydrogen bonds and van der Waals interactions. This work will deepen our understanding of the stability of ICM-102 under high pressure and provide a helpful reference for its potential detonation applications. All simulations, including geometry optimization and vibration analysis under quasi-hydrostatic pressure, were conducted using the CP2K code. The PBE function and the Goldk-Teter-Hutter (GTH) pseudopotential with the double-ζ-with-polarization (DZVP) basis set were employed. Additionally, the semiempirical dispersion correction D3 (BJ) was used to account for the intermolecular dispersion force. The simulations were performed under periodic boundary conditions, with a finest grid level cutoff set to 400 Ry for the Γ point. The Broyden-Flecher-Goldfarb-Shanno (BFGS) optimization method was used, with tighter convergence criteria applied for the subsequent calculations of infrared spectra. Finally, the wave-function analysis, such as non-covalent interaction and LBO, was conducted using the Multiwfn and VMD packages.

Theoretical insight into physical characteristics of lead-free perovskites Rb2TlSbX6 (X = Cl, Br, I) for optoelectronic devices.

Novel optoelectronic and thermoelectric properties with broad compositional range, non-toxic nature and structural stability make halide-based double perovskites fascinating for flexible optoelectronic devices. In this work, the structural electronic, optical and transport properties of Rb2TlSbX6 (X = Cl, Br, I) were studied using density functional theory for optoelectronic devices. The elastic analysis demonstrates ductile nature, mechanical stability, anisotropic behaviour and feasibility for flexible optoelectronic devices. The band structure study using Tran-Blaha-modified Becke-Johnson (TB-mBJ) potential shows that all studied materials have direct bandgap. In addition, the bandgap of Rb2TlSbCl6 is more appropriate for optoelectronic devices. The small loss and maximum absorption in visible regions make these materials prime candidates for optoelectronic devices. The transport features indicate that all the studied double perovskites reflect p-type semiconducting behaviour as highlighted by positive Seebeck coefficient values. Furthermore, the high power factor values of Rb2TlSbX6 (X = Cl, Br, I) double perovskites make them suitable for thermoelectric device applications at high temperatures. Based on electronic optical and thermoelectric properties Rb2TlSbCl6 is the best candidate for flexible optoelectronic devices. In this paper, structural optimization of Rb2TlSbX6 (X = Cl, Br, I) double perovskites was conducted utilizing the Wien2k software based on first principle calculations with Perdew-Burke-Ernzerhof's generalized-gradient approximation (PBE-sol approximation). The TB-mBJ potential was employed to compute the accurate band gap of studied materials. The thermoelectric properties are evaluated with BoltzTraP code, showing a predominance of P-type charge carriers in all studied perovskites. This methodological strategy verifies the material's remarkable stability and optical properties and offers a solid framework for examining its potential in optoelectronic devices.

Oxygen-assisted enhancing magnetism of cobalt-doped MoS2 and MoS2/graphene by first-principles calculation

The electronic structure and the magnetic properties are performed on Co doped MoS2 (MoS2-Co) and Co doped MoS2/graphene (MoS2/Gr-Co) systems based on the first principles calculations. When two Mo atoms are substituted by two Co atoms, the magnetic moments of two Co co-doped MoS2 (MoS2-2Co) and MoS2/Gr (MoS2/Gr-2Co) are 5.96 µB and 6.40 µB. The magnetic moment of MoS2-2Co increases by 0.44 µB and the transition from half-metal to metal occurs after introducing the graphene layer. Further introducing an O atom in MoS2-2Co and MoS2/Gr-2Co, the hybridization between Co-3d and O-2p is significantly stronger than that between Co-3d and S-3p.

Transfer learning relaxation, electronic structure and continuum model for twisted bilayer MoTe2

Large-scale moiré systems are extraordinarily sensitive, with even minute atomic shifts leading to significant changes in electronic structures. Here, we investigate the lattice relaxation effect on moiré band structures in twisted bilayer MoTe2 with two approaches: (a) large-scale plane-wave basis first principle calculation down to 2.88°, (b) transfer learning structure relaxation + local-basis first principles calculation down to 1.1°. We use two types of van der Waals corrections: the D2 method of Grimme and the density-dependent energy correction, and find that the density-dependent energy correction yields a continuous evolution of bandwidth with twist angles. Based on the above results. we develop a complete continuum model with a single set of parameters for a wide range of twist angles, and perform many-body simulations at ν = −1, −2/3, −1/3.

Exploring high-performance environmental barrier coatings for rare earth silicates: A combined approach of first principles calculations and machine learning

RE2Si2O7 is promising materials for environmental barrier coating (EBC), but the vast phase space poses challenges for the screening of RE2Si2O7. It follows that a combined approach of first principles calculations and machine learning is proposed for this problem, with establishing a comprehensive database comprising β-, γ- and δ-RE2Si2O7 (RE=La–Lu, Y, Sc) and correlating their mechanical/thermal properties on structural characteristics. It is revealed the [O3Si–O–SiO3] structure and polyhedron distortion affect mechanical properties of RE2Si2O7, while criteria for selecting RE2Si2O7 with low thermal conductivity are identified, including complex crystal structures, chemical bond inhomogeneity, and strong non-harmonic lattice vibrations. Also, the machine learning model accurately predicts the coefficient of thermal expansion (CTE) and minimum thermal conductivity (λmin) of RE2Si2O7, with volume and mass variations identified as critical factors, respectively. This integrated approach efficiently screens RE2Si2O7 for EBC application and enables rapid assessments of their thermal properties.

Structural, electronic, thermoelectric and optical properties of 2D hexagonal beryllium telluride under DFT investigation

In this study we have investigated structural, electronic, thermoelectric and optical properties of monolayer beryllium telluride compound in the hexagonal lattice phase (h-BeTe) using first principle calculations under density functional theory (DFT) approach. Using the frequency dependent phonon dispersion curves, we have analyzed the stability of the h-BeTe compound. The investigation of structural properties, including density of states (DOS) and band structure, demonstrates that h-BeTe is a direct bandgap semiconductor material with bandgap value of 3.054 eV. The h-BeTe compound exhibits exceptional thermoelectric behavior for a temperature range of 50–800 K, as confirmed by the calculated thermoelectric parameters, including thermal conductivity, electrical conductivity, Seebeck coefficient and figure of merit (ZT). It is vital that h-BeTe exhibits exceptional thermoelectric properties specifically, the figure of merit (ZT > 0.9) provides the efficiency of h-BeTe compound in temperature range of 300–800 K. The optical properties of h-BeTe are investigated for the first time with its interaction in applied external electric field based on various optical parameters such as real and imaginary dielectric constant, refractive index n(ω), extinction coefficient k(ω), absorption coefficient α(ω) and reflectivity R(ω). The optical properties analysis reveals the monolayer hexagonal beryllium telluride to be mostly active in the visible-UV spectrum. These findings have the potential to foster researchers to explore h-BeTe compound experimentally for possible optoelectronic applications.

Component design and stable SESAM mode-locking of the disorder middle entropy Yb:CaSrBaF6 single crystal.

To the best of our knowledge, this is the first report on continuous and passively mode-locked operation of the multi-component fluoride CaSrBaF6 crystal. A novel disorder laser material, Yb:CaSrBaF6 (Ca0.33Sr0.33Ba0.33F2) of multi-component middle entropy crystal was designed and grown by temperature gradient technique (TGT) for the first time. X-ray diffraction (XRD) and X-ray fluorescence (XRF) analysis of Yb:CaSrBaF6 crystal reveals that Ca2+, Sr2+, and Ba2+ of near equal atomic ratio (1:1:1) have formed a homogeneous single-phased fluorite solid solution. The first principle calculation further shows that Ca2+, Sr2+, Ba2+ ions tend to be evenly distributed in the matrix crystal. The total formation energy is the lowest -547.17 ev and the structure is also the most stable at this time. The spectral properties of the crystal are systematically characterized. The emission cross section of 2F5/2→2F7/2 transition at 1040 nm is 0.62 × 10-20 cm2 with the larger full width at half maximum (FWHM) of 60.5 nm. The evenly disordered distribution of various cations and lattice distortion effect leads to the more diverse local structure and the diversity of luminescence, which can cause non-uniform broadening of the spectrum. Meanwhile, the Yb:CaSrBaF6 crystal generated a continuous wave (CW) output power of 1.128 W, corresponding to a slope efficiency of 32% and an optical-to-optical conversion efficiency of 28.7% at 1055.4 nm. By implementing a semiconductor saturable absorber mirror (SESAM) for stable mode-locked laser operation, when the absorbed pump power reached 3.79 W, the laser ran into continuous wave mode-locking (CWML) regime, the maximum average output power of 123 mW was generated and the pulse duration of 89 ps was achieved at a pulse repetition rate of 54.6 MHz, with a pulse energy of 2.25 nJ and a pulse peak power of 25 W. Better laser performance could be expected after optimizing pump core diameter and elimination of dispersion. All results show that Yb:CaSrBaF6 crystal is regarded as a what we believe to be novel laser materials, which also provide a reference for the development of disordered material and other rare earth ions doping.

Study of optoelectronic and thermoelectric properties of K2XSbCl6 (X= In, Au) double perovskites for energy conversion devices: A DFT insight

Density functional theory (DFT) method based on first principles calculations are performed to explore the novel halide perovskites K2InSbCl6 and K2AuSbCl6. This study explores them for the first time to investigate their structural, electronic, optical, and thermoelectric properties. After relax the structure, we computed some parameters such as lattice constant (21.2195, 20.256) bohr, ground states energy (−32681.329187 eV, −59010.453287 eV), and formation energy (−2.06 eV, −1.433 eV) observed for K2XSbCl6 (X = In, Au) compounds respectively. The K2InSbCl6 reveals a direct band gap (1.03 eV), while K2AuSbCl6 shows an indirect band gap (1.01 eV). Hence, both materials express semiconducting behavior. Furthermore, the calculated optical characteristic is favorable for optoelectronics devices. The real dielectric function ε1(ω) for K2XSbCl6 (X = In, Au) 4.0 and 4.25 and the absorption coefficient shows maximum absorption in the visible region. The thermometric response of both compounds is calculated with Boltzmann's theory. To check the material efficiency, considered the thermal parameters, electrical conductivity, thermal conductivity, Seebeck coefficient, and power factor. The zT values of K2InSbCl6 is 0.74 and 0.77 for K2AuSbCl6. The present study of these novel compounds provides an overview of the physical properties of optoelectronics and thermoelectric applications.