Band Structure Research Articles

Ab initio analysis of structural, electronic, magnetic, thermodynamic, and elastic properties of Half Heusler alloys ZMnAs (Z = Be, Mg) for spintronics applications

In this study, the structural, electronic, magnetic, thermodynamic, and elastic attributes of ZMnAs (Z = Be, Mg) have been investigated. These Half-Heusler alloys exhibit stability in the ferromagnetic state (FM), as demonstrated by optimization-related energy release. The half-metallicity (HM) of these compounds is examined through the band structures and density of states (DOS). In addition, the crystal field and exchange energies are reported to confirm the control of electron spin. Additionally, the double exchange process and exchange constants were premeditated. In this case, ferromagnetism (FM) is caused by the quantum exchange of electrons, as evidenced by the negative pd exchange energy and the exchange constants, rather than being a result of clustering effects. The quasi-harmonic Debye model, included within the Gibbs code, was utilized to calculate the thermodynamic properties. These two compounds are mechanically stable and show ductile nature confirmed by the value of Poisson's ratio (v), Pugh's ratio (B/G), and Cauchy pressure (CP), which demonstrates the ability to withstand substantial plastic deformation before fracturing. Based on our calculations, the half-metallic (HM) nature, thermodynamic, ferromagnetic, ductile, and high inherent magnetic moment have been evaluated. These alloys are crucial in the advancement of spintronics and renewable energy systems.

Exploring the effect of strong electronic correlations in Seebeck Coefficient of the NdCoO3 compound : Using experimental and DFT+U approach

The presence of complexity in the electronic structure of strongly correlated electron system NdCoO3 (NCO) have sparked interest in the investigation of its physical properties. Here, we study the Seebeck coefficient (α) of NCO by using the combined experimental and DFT+U based methods. The experimentally measured Seebeck coefficient is found to be ∼444 μ V/K at 300 K, which decreases to 109.8 μ V/K at 600 K. In order to understand the measured Seebeck coefficient, we have calculated the PDOS and band structure of the NCO. Furthermore, the calculated occupancy of 6.4 for Co 3d orbitals and presence of large unoccupied O 2p states indicate the covalent nature of the bonding. Apart from this, the maximum effective mass is found to be 36.75 (28.13) me for the spin-up (dn) channel in conduction band indicates the n-type behaviour of the compound in contrast to our experimentally observed p-type behaviour. While, the calculated Seebeck coefficient at the temperature-dependent chemical potential (μ) at 300 K shows the p-type behaviour of the compound. Fairly good agreement is seen between the calculated and measured values of α at U ff = 5.5 eV and U dd = 2.7 eV. The maximum power factor (PF) is found to be 47.6 (114.4)×1014 μW K −2cm−1 s −1 at 1100 K, which corresponds to p (n)-type doping of ∼1.4 (0.7)×1021 cm−3. This study suggests the importance of strong on-site electron correlation in understanding the thermoelectric property of the compound

Self-induced optical pulling in complex photonic band structure

The photonic band gap effect has been proposed to achieve a gradient-induced long-range optical pulling force, but how the properties of the photonic band gap affect the optical pulling force remains to be revealed. In this work, based on the theory of complex photonic band and Einstein–Laub formulation of force density, a concise formula is developed to investigate such unusual optical pulling force. It indicates that the optical pulling force is mainly decided by the imaginary part of the wave vector of evanescent mode in the photonic band gap and the refractive index of the object. A larger imaginary part of the wave vector and a higher refractive index of the object typically result in a larger optical pulling force, which is verified by the numerical simulation. In addition, a critical length is defined to predict the occurrence of optical pulling force. Our work gives an insight into such an optical pulling force based on the complex photonic band and offers guidance for achieving a larger optical pulling force, which is very beneficial to optical sorting and optical conveying.

X[formula omitted]CoH[formula omitted] (X = Ca, Sr) for hydrogen storage: First-principles computations

The structural, electronic, elastic, optical, phonon, and thermo-physical properties of the tetragonal X2CoH5 (X = Ca, Sr) hydrogen storage compounds were thoroughly examined using first-principles calculations. The negative formation enthalpies (−76.03 kJ/mol.H2 for Ca2CoH5 and −72.55 kJ/mol.H2 for Sr2CoH5) highlight the structural stability of these materials. Phonon calculations revealed no imaginary frequency modes, confirming the dynamic stability of X2CoH5. The mechanical stability of Ca2CoH5 and Sr2CoH5 was evidenced by the compliance of the elastic constants with Born stability criteria. The electronic band structure indicates that Ca2CoH5 and Sr2CoH5 are direct bandgap semiconductors with narrow bandgaps of ∼0.27 and 0.34 eV, respectively. The appraisal of Poisson’s ratio (ν = 0.22 for X = Ca and 0.23 for Sr) and Pugh’s ratio (B/G = 1.47 for X = Ca and 1.56 for Sr) suggests that both metal hydrides exhibit brittle mechanical behavior. Moreover, 3D plots of Young’s modulus (E), shear modulus (G), linear compressibility (β), and Poisson’s ratio (ν) uncover anisotropy within X2CoH5. The hydrogen storage capabilities were scrutinized, and the present materials feature excellent volumetric hydrogen density (95.65 gH2l−1 for Ca2CoH5 and 80.24 gH2l−1 for Sr2CoH5), moderate gravimetric hydrogen density (3.38 wt% for Ca2CoH5 and 2.06 wt% for Sr2CoH5) and high hydrogen desorption temperature (584 K for Ca2CoH5 and 558 K for Sr2CoH5). Notably, the obtained volumetric hydrogen densities are in line with the volumetric capacity criteria set by the U.S. Department of Energy (DOE) for 2025. Finally, the optical and thermo-physical characteristics of X2CoH5 compounds were also investigated in this work.

Enhanced sunlight-driven photocatalysis of non-metal doped zinc oxide via wet impregnation for the removal of organic compounds

Zinc oxide (ZnO), a commonly used photocatalyst, suffers from the rapid recombination of photogenerated charge carriers, and the inability to harvest visible light. Therefore, the green synthesized ZnO from Garcinia mangostana pericarp is modified via non-metal (X) doping of N, P, S, Br, and B with a mass content of 5 % to tackle the aforementioned. The obtained materials were characterized through various modern characterization techniques. The results reveal that amongst the X-doped sample, ZnO-B demonstrates the highest photocatalytic performance. The characteristics of ZnO include good crystallinity as well as a low band gap energy of 2.094 eV, revealing an enhanced visible light absorption activity of the sample. The photoactivity of surveyed ZnO-B was investigated through the degradation of malachite green, methyl orange, and tetracycline, achieving a removal rate of 96.29, 86.59, and 90.32 %, respectively. Simultaneously, the antibacterial properties of the ZnO-X were evaluated for Staphylococcus aureus under sunlight illumination. Moreover, the photocatalysis mechanism of the studied materials was elucidated through the band structure, toxicity, and total organic carbon removal of the post-catalysis solution. The selected boron-doped zinc oxide catalyst also showed excellent reusability after 10 cycles of photocatalysis, retaining ∼ 80 % of its original activity. The obtained results reveal the potential application of non-metal-doped zinc oxide in environmental remediation and water disinfection.

Design of TiO2-based bi-functional catalyst and the catalytic mechanism of enhanced hydrazine borane hydrolysis for hydrogen production

In this study, a scheme of photocatalytic coupled metal catalytic synergistic enhancement of hydrazine borane hydrolysis is proposed, the catalytic reaction mechanism for hydrogen production from hydrazine borane hydrolysis is revealed. In addition, the effects of solvent property, external electric field conditions on the stability of N2H4BH3 molecule are also investigated systematacially. The results show that the band structure of pure TiO2 can be modulated by heterogeneous element N, C, Ni, Ru, the modification effect of co-doping with heterogeneous alloy elements (eg. NiPt@N–TiO2) is best in all doping schemes. The hydrolysis reaction of -BH3 of N2H4BH3 catalyzed by Pt metal is a stepwise dehydrogenation reaction, and the energy barrier of the reaction rate-determining of the B–N bond breakage is 50.49 kcal/mol. There are two possible cleavage reaction pathways for N2H4, which are hydrogen-producing pathway and ammonia-producing pathway, the energy barrier for the reaction rate-determining step is 67.06 kcal/mol and 82.51 kcal/mol, respectively, the hydrogen production reaction takes precedence over the ammonia production reaction. OH− solution is best among the neutral aqueous solution, rich H+, NH4+ and NaOH solution in B–H bond activation of N2H4BH3 molecule, the external electric field can promote the activation of B–H bond in hydrazine borane hydrolysis system, which is positive factor in improving the performance of hydrazine borane hydrolysis.

Novel S-scheme β-Cu2V2O7/Ni/Pg-C3N4 heterojunction photocatalyst for sunlight-induced degradation of RhB

A novel S-scheme β-Cu2V2O7/Ni/Pg-C3N4 nanocomposite photocatalyst has been advantageously established by propelling β-Cu2V2O7 nanoparticles (NPs) on the top layer of porous graphitic carbon nitride (Pg-C3N4) nanosheets (NSs) using a facile co-precipitation approach. Implementing photoelectrochemical and physicochemical techniques, the crystallinity, purity, optical quality, morphology, chemical composition, and charge separation efficiency of the produced samples were examined. The outcomes indicate that metallic Ni and β-Cu2V2O7 NPs were perfectly encapsulated onto the Pg-C3N4 NSs and well-matched band structures between both semiconductors facilitate the creation of an S-scheme charge transfer path. The fabricated pristine and β-Cu2V2O7/Ni/Pg-C3N4 composite samples were utilized as a catalyst for the removal of rhodamine B (RhB) dye under sunlight irradiation. The β-Cu2V2O7/Ni/Pg-C3N4 nanocomposite exhibits exceptional activity within 60 min of radiation exposure (RhB- 98.56%), whereas β-Cu2V2O7 and Pg-C3N4 show reduced activity (RhB-34.4% and 45.68%). The favourable impact of S-scheme nanocomposite establishment boosted photocatalytic behavior using the intrinsic electric field among Pg-C3N4 NSs and β-Cu2V2O7 and surface plasmon resonance (SPR) effect of metallic Nickel (Ni) NPs for delivering e− and h+ pairs and prolonging the life of charge carriers. According to radical scavenging experiments •O2− is the primary reactive species followed by •OH radicals. The produced nanocomposite has the potential to be employed in large-scale photocatalytic water treatment, as evidenced by the photocatalyst's excellent efficiency and reusability after five consecutive experiments.

Numerical simulation of all inorganic CsPbIBr2 perovskite solar cells with diverse charge transport layers using DFT and SCAPS-1D frameworks

All inorganic CsPbX3 perovskites (X = Br and I) are excellent candidates for stable and efficient perovskite solar cells (PSCs). Among them, CsPbIBr2 demonstrated the most balanced characteristics in terms of band gap and stability. Nevertheless, the power conversion efficiency (PCE) of CsPbIBr2-based solar cells is still far from that of Hybrid PSCs, and more research is required in this aspect. Herein, DFT and SCAPS-1D frameworks are employed to explore the optimized device configurations of CsPbIBr2 PSCs. DFT is used to explore the structural and optoelectronic characteristics of CsPbIBr2, while SCAPS-1D is employed to examine various device structures of CsPbIBr2-based PSCs. The band structure demonstrated the direct band gap nature of CsPbIBr2 with a band gap of 2.12 eV. Moreover, we have used TiO2, SnO2, ZnO, WS2, IGZO, CeO2, In2S3, and CdS as ETLs, and Cu2O, CuI, MoO3, NiO, CuSCN, CuSbS2, CBTS, CFTS, and CuO as HTLs for identifying the best ETL/CsPbIBr2/HTL configurations. Among 72 device combinations, eight sets of PSCs are identified as the most efficient configurations. In addition, the influence of various parameters like the thickness of various layers, doping concentration, perovskite defect density, ETLs and interfaces, series resistances, shunt resistances, and temperature on device performance have been comprehensively studied. The results demonstrate Cu2O as the best HTL for CsPbIBr2 with each ETL, and PSC with device structure ITO/WS2/CsPbIBr2/Cu2O/C exhibited the highest PCE of 16.53%. This comprehensive investigation will provide new path for the development of highly efficient all-inorganic CsPbIBr2 solar cells.

Exciton-Exciton Interactions in Van der Waals Heterobilayers

Exciton-exciton interactions are key to understanding nonlinear optical and transport phenomena in van der Waals heterobilayers, which emerged as versatile platforms to study correlated electronic states. We present a combined theory-experiment study of excitonic many-body effects based on first-principle band structures and Coulomb interaction matrix elements. Key to our approach is the explicit treatment of the fermionic substructure of excitons and dynamical screening effects for density-induced energy renormalization and dissipation. We demonstrate that dipolar blueshifts are almost perfectly compensated by many-body effects, mainly by screening-induced self-energy corrections. Moreover, we identify a crossover between attractive and repulsive behavior at elevated exciton densities. Theoretical findings are supported by experimental studies of spectrally narrow, mobile interlayer excitons in atomically reconstructed, h-BN-encapsulated MoSe2/WSe2 heterobilayers. Both theory and experiment show energy renormalization on a scale of a few meV even for high injection densities in the vicinity of the Mott transition. Our results revise the established picture of dipolar repulsion dominating exciton-exciton interactions in van der Waals heterostructures and open up opportunities for their external design. Published by the American Physical Society 2024

Synergistic photocatalysis for bacteria inactivation and organic pollutant removal by S-scheme heterojunction InVO4/Bi5O7I: Performance evaluation and mechanism investigation

The low efficiency of charge carrier separation is a major limitation hindering the application of photocatalytic technology. Constructing S-scheme heterojunction photocatalysts not only effectively promotes the separation of charge carriers, but also maximizes the oxidative and reductive capabilities of the two monomers. In this study S-scheme heterogeneous InVO4/Bi5O7I photocatalyst was synthesized by hydrothermal method combined with calcination. The optimal sample 20 % InVO4/Bi5O7I can completely deactivate Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) in 30 min, remove 20 mg/L TC 76.0 % in 60 min and 20 mg/L BPA 93.0 % in 90 min. Intermediate products of TC and BPA degradation were detected using LC-MS, and possible degradation pathways were proposed. The photocurrent and electrochemical impedance spectroscopy (EIS) tests confirm that InVO4/Bi5O7I exhibits excellent photocurrent intensity and photocarrier migration ability, which are crucial reasons for the enhancement of the photocatalytic performance of the InVO4/Bi5O7I composite. Capture experiments indicate that OH, O2−, h+ and e−are reactive species. EPR further confirms the generation of OH and O2−. Combined with Kelvin probe force microscopy (KPFM) and band structure analysis, it is proposed that InVO4/Bi5O7I has an S-scheme charge transfer mechanism.

First-Principles Calculations on Electronic, Optical, and Phonon Properties of γ-Bi2MoO6.

The wide band gap γ-Bi2MoO6 (BMO) has tremendous potential in emergent solar harvesting applications. Here we present a combined experimental-first-principles density functional theory (DFT) approach to probe physical properties relevant to the light sensitivity of BMO like dynamic and structural stability, Raman and infrared absorption modes, value and nature of band gap (i.e., direct or indirect), dielectric constant, and optical absorption, etc. We solvothermally synthesized wide band gap Pca21 phase pure BMO (≳3 eV) for two different pH values of 7 and 9. The structural parameters were correlated with the stability of BMO derived from elastic tensor simulations. The desired dynamical stability at T = 0 K was established from the phonon vibrational band structure using a finite difference-based supercell approach. The DFT-based Raman modes and phonon density of states (DOS) reliably reproduced the experimental Raman and infrared absorption. The electronic DOS calculated from Heyd-Scuseria-Ernzerhof HSE06 with van der Waals (vdW) and relativistic spin-orbit coupling (SOC) corrections produced a good agreement with the band gap obtained from diffuse reflectance spectroscopy (DRS). The optical absorption obtained from the complex dielectric constant for the HSE06+SOC+vdW potential closely resembled the DRS-derived absorption of BMO. The BMO shows ∼43% photocatalytic efficiency in degrading methylene blue dye under 75 min optical illumination. This combined DFT-experimental approach may provide a better understanding of the properties of BMO relevant to solar harvesting applications.

Boosting the Activation of Molecular Oxygen and the Degradation of Rhodamine B in Polar-Functional-Group-Modified g-C3N4.

Molecular oxygen activation often suffers from high energy consumption and low efficiency. Developing eco-friendly and effective photocatalysts remains a key challenge for advancing green molecular oxygen activation. Herein, graphitic carbon nitride (g-C3N4) with abundant hydroxyl groups (HCN) was synthesized to investigate the relationship between these polar groups and molecular oxygen activation. The advantage of the hydroxyl group modification of g-C3N4 included narrower interlayer distances, a larger specific surface area and improved hydrophilicity. Various photoelectronic measurements revealed that the introduced hydroxyl groups reduced the charge transfer resistance of HCN, resulting in accelerated charge separation and migration kinetics. Therefore, the optimal HCN-90 showed the highest activity for Rhodamine B photodegradation with a reaction time of 30 min and an apparent rate constant of 0.125 min-1, surpassing most other g-C3N4 composites. This enhanced activity was attributed to the adjusted band structure achieved through polar functional group modification. The modification of polar functional groups could alter the energy band structure of photocatalysts, narrow band gap, enhance visible-light absorption, and improve photogenerated carrier separation efficiency. This work highlights the significant potential of polar functional groups in tuning the structure of g-C3N4 to enhance efficient molecular oxygen activation.

Facilistic preparation of zinc oxide nanoarrays on nickel foam via a one-step chemical bath method for photocatalysis

One-dimensional ZnO nanoarrays (ZnO NAs) were prepared on nickel foam using a one-step chemical bath deposition method. SEM and XRD confirmed the successful preparation of ZnO nanoarrays. TEM and Raman spectroscopy confirmed the preferential orientation of the ZnO nanorods along the (002) crystal plane. The Ni/ZnO NAs composites exhibited excellent photocatalytic degradation activity for ciprofloxacin (CIP) under UV light. UV–visible diffuse reflectance and transient photocurrent response characterization revealed that compared with ZnO nanorod powder, the Ni/ZnO NA composites increased the light absorption and reduced the complexation rate of photogenerated electron-hole pairs, thus improving the photocatalytic efficiency. In addition, the electron work functions of the two substances were calculated by using the crystal faces of Ni (111) and ZnO (002), and the calculation results confirmed the electron transfer paths. Electron transfer pathways further confirmed the possible reaction mechanism of Ni/ZnO NA degradation of CIP. Finally, Mott–Schottky tests were used to investigate the structure of the energy bands of the material and reveal its photocatalytic mechanism.

The analysis of sarcosine phosphate single crystal based on polarized IR and Raman spectra

For the first time, the room temperature polarized IR reflection and Raman spectra of sarcosine phosphate (sar)·H3PO4, in the form of an oriented single crystal have been measured. The polarized spectra are discussed with respect to the crystal structure (X-ray diffraction) data and the literature data on the normal coordinate analysis of the zwitterionic and cationic forms of the sarcosine molecule. Based on the analysis of the spectra and transition dipole moment calculations for each internal mode with respect to the experimental X(a), Y(b) and Z(c) axes, we have been able to determine the directionality and strength of the complicated hydrogen bonds network in the crystal. The A-B-C band structure of the OH stretching vibrations in the strongest hydrogen bonds (HBs) has been assigned. Independent interactions of each HB with light are confirmed based on their polarization properties. The differences within the band of carboxyl group components are ascribed to a rather strong Davydov-type interaction between the carboxyl groups in the title crystal, they may also be caused by participation of the carboxyl-oxygen atom in the medium-strong HB with phosphate-oxygen. These studies are interesting from the point of view of designing strategy for the molecular engineering of new compounds with strong hydrogen bonds, new phase-change materials, as well as crystals with improved optical, magnetic and nonlinear optical properties.

Cu-doped ZnCdS-based photocatalyst for efficient photocatalytic hydrogen production by photothermal assistance

In solar energy utilization, photocatalytic hydrogen production has been widely researched. To address issues such as low efficiency of photocatalysts, Cu-doped Zn0.5Cd0.5S composite photocatalysts were prepared using a hydrothermal method for photocatalytic hydrogen production. The Cu/Zn0.5Cd0.5S photocatalyst was characterized using XRD, XPS, SEM, TEM, UV–vis-DRS, fluorescence spectrophotometer, and electrochemical workstation. The results indicate that Cu doping alters the crystal and band structures of Zn0.5Cd0.5S. Hydrogen production experiments were conducted under xenon lamp irradiation, and at 45 °C, the highest hydrogen production rate was 2.72 and 1.63 times that of single Zn0.5Cd0.5S and Cu-doped Zn0.5Cd0.5S at room temperature (25 °C), respectively. Cu doping imparted a photothermal effect to the photocatalytic hydrogen production experiment, enhancing its efficiency.Cu doping captured electrons by replacing some Zn, constructing an internal electric field, forming defect energy levels, which hindered electron-hole recombination. Additionally, Cu ions acted as a plasma, inducing a plasma effect during hydrogen production, accelerating the rate of solar energy conversion to thermal energy, thus improving hydrogen production efficiency. This research not only provides a photocatalyst for photocatalytic hydrogen production but also utilizes it for photothermal synergistic catalysis.

Design and optimization of (FA)2BiCuI6-based double perovskite solar cells using kesterite CBTS as hole transport layer for high power conversion and quantum efficiency

This work introduces the design of a novel architecture for double perovskite solar cells (DPSCs) utilizing (FA)2BiCuI6, known for its enhanced stability relative to single perovskite materials for production of efficient, ultra-thin solar cells. The proposed architecture features a unique device configuration of ITO/WO3/(FA)2BiCuI6/Cu2BaSnS4/W, incorporating a Kesterite type Cu-based quaternary chalcogenide material, Cu2BaSnS4 known as CBTS, is used as hole transport layer (HTL) with a bandgap of 1.9 eV, WO3 as the electron transport layer (ETL) with a 2.6 eV bandgap, and (FA)2BiCuI6 as the absorber layer with a 1.55 eV bandgap. The study provides an in-depth theoretical analysis of the energy band structure, defects, and quantum efficiency of the DPSC, highlighting the device’s post-optimization photovoltaic parameters. Remarkably, the optimized DPSC demonstrated superior performance with a PCE of 24.63%, Voc of 1.16 V, Jsc of 25.67 mA cm−2, and FF of 82.87%. The research also explores the effects of various factors on photovoltaic performance, including temperature, interface defect, and generation and recombination rates, as well as work function of back contact materials. The results underscore the exceptional potential of (FA)2BiCuI6, especially when combined with the HTL CBTS, in significantly reducing sheet resistance and enhancing the overall performance of solar cells. The design is validated using the SCAPS-1D simulation software tool.

Nitrogen: A promising doping strategy for high-performance ovonic threshold switching selectors

The Ovonic Threshold Switching (OTS) selector serves as an essential component in the development of three-dimensional high-density memory integration technology. Nevertheless, the state-of-the-art high-performance OTS materials usually contain toxic elements such as arsenic (As), posing significant risks to both environmental and human health. Nitrogen (N), which belongs to the same group as arsenic (As), has emerged as a highly promising alternative for As doping. However, the underlying mechanisms that govern N-based OTS materials have not yet been extensively investigated. In this study, we delve into the effects of N doping on the structural, bonding, and electronic properties of amorphous GeSe (a-GeNSe) by ab initio molecular dynamics simulations to bridge the knowledge gap. Our findings indicate that upon N doping in a-GeSe, the formation of robust Ge-N bonds, along with N-centered tetrahedral and triangular structures, resulting in the sluggish atomic movement that enhances the thermal stability and endurance of a-GeNSe. The OTS characteristics are significantly influenced by the material’s electronic band structure, and thus the relatively slow performance drift can be attributed to the stabilization of mid-gap states, a result of N doping which effectively slows down the aging process of chalcogenide glass. Moreover, the increased mobility gap in a-GeNSe raises the threshold voltage (Vth), making it more compatible with commercially available phase-change memory materials. Our findings reveal the extensive impact of the N element on a typical OTS material and offer valuable perspectives for alternative doping strategies that could potentially supplant As practices.

An ab-initio investigation of physical characteristics of GdSc1-xTMxO3(TM=Ti; x=0.25, 0.5, 0.75) for photo influenced (NIR)memory storage and allied devices

In the present study, we have computed the structural, electronic, and optical characteristics of pristine GdScO3 and GdSc1-xTMxO3 (TM = Ti; x = 0.25, 0.5, 0.75) for improved performance of Resistive Random Access Memory (RRAM) devices. All calculations have been performed using the Tran Balha-modified Becke Johnson (TB-mBJ) approximation within the framework of the WEIN2K simulation package. Herein, the effect of Ti-dopant (transition metal, i.e., TM) with varying concentrations has been observed, especially in tuning the energy band gap. The structural analysis of composites reveals structural stability and a significant reduction in bulk modulus with increasing dopant concentration, leading to enhanced electrical conductivity. The band structure analysis reveals that the band gap tends to decrease with increasing concentrations of Ti-dopant.As regards total density of states (TDOS), it has been found that with increasing concentrations of Ti, dopant extra states appear in the conduction band. This is the reason behind the formation of the conducting filaments (CF) within the active layer of RRAM devices. The partial density of states (PDOS) elaborates that for all studied composites, the formation of the conduction band (C.B.) and valence band (V.B.) is a consequence of the hybridization of Sc-3d, Gd-5d, and Ti-4d states, along with the minute contribution of O-2p states. Optical characteristics disclose the photoresponse of all studied composites, wherein GdSc0.25Ti0.75O3 exhibits wide range absorption, henceforth making it a making it a more suitable candidate for photoinfluencing, especially in near infrared (NIR) RRAM devices.

High Electron Mobility in Si-Doped Two-Dimensional β-Ga2O3 Tuned Using Biaxial Strain.

Two-dimensional (2D) semiconductors have attracted much attention regarding their use in flexible electronic and optoelectronic devices, but the inherent poor electron mobility in conventional 2D materials severely restricts their applications. Using first-principles calculations in conjunction with Boltzmann transport theory, we systematically investigated the Si-doped 2D β-Ga2O3 structure mediated by biaxial strain, where the structural stabilities were determined by formation energy, phonon spectrum, and ab initio molecular dynamic simulation. Initially, the band gap values of Si-doped 2D β-Ga2O3 increased slightly, followed by a rapid decrease from 2.46 eV to 1.38 eV accompanied by strain modulations from -8% compressive to +8% tensile, which can be ascribed to the bigger energy elevation of the σ* anti-bonding in the conduction band minimum than that of the π bonding in the valence band maximum. Additionally, band structure calculations resolved a direct-to-indirect transition under the tensile strains. Furthermore, a significantly high electron mobility up to 4911.18 cm2 V-1 s-1 was discovered in Si-doped 2D β-Ga2O3 as the biaxial tensile strain approached 8%, which originated mainly from the decreased quantum confinement effect on the surface. The electrical conductivity was elevated with the increase in tensile strain and the enhancement of temperature from 300 K to 800 K. Our studies demonstrate the tunable electron mobilities and band structures of Si-doped 2D β-Ga2O3 using biaxial strain and shed light on its great potential in nanoscale electronics.

Material Design and Discovery in Full-Heusler Compounds: A Comprehensive First-Principles Analysis of XMg2Hg, XMgHg2, and X2MgHg (X = Sc, Li)

This study conducts a comprehensive first-principles analysis of the structural, mechanical, phonon dispersion, and electronic properties of XMg2Hg, XMgHg2, and X2MgHg (X = Sc and Li) compounds. Using energy-volume curves, cohesive and formation energy, and phonon dispersion analyses, we confirm the stability of these compounds. Our calculations reveal that Li2MgHg and ScMg2Hg are more stable in the cubic structure with space group F4¯3m (216), whereas other compounds are stable in the Fm3¯m (225) structure. Phonon dispersion calculations indicate dynamical stability for all compounds except Li2MgHg in the Fm3¯m structure and Sc2MgHg and LiMg2Hg in the cubic structure with space group F4¯3m (216). Mechanical stability is confirmed through the calculation of elastic constants, with Sc-based compounds showing higher bulk modulus, shear modulus, and Young's modulus compared to Li-based compounds. Electronic properties, analyzed through density of states and band structure calculations, confirm the metallic nature of these compounds, with significant contributions from Mg atoms at the Fermi energy. The study also identifies distinct electronic features such as flat electron bands and a Dirac point at the Gamma point for ScMgHg2​. Pressure-dependent studies indicate these materials are normal metals without topological phase transitions.