Search Results (2,266)

Lead-free halide double perovskites have emerged as promising candidates for sustainable optoelectronic and thermoelectric applications due to their tunable band gaps, high stability, and non-toxic nature. In this work, we systematically investigate the structural, electronic, optical, and thermoelectric properties of novel double perovskite compounds Rb₂InCuX₆ (X = F, Cl, Br) using density functional theory (DFT) combined with spin–orbit coupling (SOC). The structural stability of these materials is confirmed by evaluating the tolerance factor, octahedral factor, and negative formation energy. Accurate band structures obtained via the modified Becke–Johnson (mBJ) potential and SOC reveal direct band gaps of 1.49 eV, 0.91 eV, and 0.56 eV for Rb₂InCuX₆ (X = F, Cl, Br), indicating their suitability for solar cell applications. Optical properties, derived from the dielectric functions calculated within the Kramers–Kronig framework over a photon energy range up to 14 eV, show strong absorption peaks in the ultraviolet region, making these materials attractive for high-frequency optical conversion devices. Furthermore, thermoelectric parameters, including the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and power factor, are computed using the BoltzTraP code. Notably, the figure of merit (ZT) approaches 0.80 for Rb₂InCuF₆, close to the ideal value of unity, demonstrating excellent thermoelectric performance over a wide temperature range (200–800 K). Our findings establish Rb₂InCuX₆ (X = F, Cl, Br) as promising lead-free double perovskites for integrated optoelectronic and thermoelectric applications. Full article

The reinforced concrete structures of many bridges and buildings in Taiwan are over 30 years old. Seismic retrofitting of these structures requires an accurate assessment of reinforcement configuration and corrosion conditions to ensure structural safety and seismic performance. In this study, a 1 GHz ground-penetrating radar (GPR) antenna was used to scan reflected signals from single- and double-row reinforcing bars embedded in concrete. Based on established principles reported in previous studies, detailed analyses were conducted, including the use of the approximate circumference method to estimate reinforcing bar dimensions and the determination of spacing between double-row reinforcing bars (6–8 cm). The synthetic aperture focusing technique was first applied to process the original GPR data matrix. Subsequently, physical parameters related to interface diffraction, such as the perimeter S of the reinforcing bar, were extracted using the dielectric constant of the material interface, the calculated power reflection coefficient, and the First Fresnel Zone. These approaches enabled more accurate estimation of reinforcing bar dimensions (e.g., equivalent to #3 bar size) and improved resolution of spacing between double-row reinforcing bars to 3–6 cm. The results demonstrate that using the synthetic aperture focusing technique to process GPR data enhances the ability to determine reinforcing bar dimensions, interpret bar spacing, and improve imaging resolution, thereby providing a reliable reference for the safety assessment of reinforced concrete structures. Full article

The advancement of electrochromic devices, including smart windows, is important for improving energy efficiency in modern society. Nickel oxide thin films are key functional materials in this technology and have attracted significant attention due to their electrochemical activity and optical properties. However, existing theoretical studies have primarily focused on crystalline NiO, while systematic understanding of Li⁺ diffusion mechanisms in amorphous NiO remains limited. In this work, first-principles calculations combined with second-generation Car–Parrinello molecular dynamics simulations and the melt-quenching method are employed to construct amorphous NiO models with varying oxygen content, enabling investigation of oxygen-dependent Li⁺ diffusion behavior. The results show that the Li⁺ diffusion coefficient increases with increasing oxygen content, accompanied by a reduction in diffusion barriers. Analysis of local structural environments further reveals that Li coordination with under-coordinated Ni–O polyhedra plays a key role in facilitating ion migration, providing atomistic insight into the observed diffusion trends. This study establishes a structure–diffusion relationship in amorphous NiO and provides atomistic understanding of how oxygen stoichiometry modulates Li⁺ transport behavior in electrochromic materials. Full article

Vanadium borate (V₃BO₆) has recently been synthesized and identified as a promising material for use in energy storage applications, particularly as a potential anode for lithium-ion batteries. However, despite previous studies highlighting its electrochemical performance, a comprehensive understanding of its intrinsic mechanical, thermal, and vibrational properties remains limited. The compound crystallizes in an orthorhombic phase with the Pnma (No. 62) space group. To explore its intrinsic physical characteristics, full geometry optimization of the unit cell and atomic positions was performed using density functional theory (DFT) within the CASTEP framework. The Perdew–Burke–Ernzerhof (PBE) functional under the generalized gradient approximation (GGA) was used to model exchange–correlation effects. A plane-wave cut-off of 408 eV and a 6 × 6 × 13 Monkhorst–Pack grid were employed to ensure numerical convergence. The optimized lattice constants (a = 9.9025 Å, b = 8.4751 Å and c = 4.5354 Å) are highly consistent with experimental data, which confirms the reliability of the computational approach adopted. The elastic behaviour was further investigated using the first-principles strain-energy method, yielding nine independent elastic constants consistent with orthorhombic symmetry. The calculated bulk and shear moduli, along with the anisotropy parameters, suggest that V₃BO₆ has a favourable balance of mechanical robustness and moderate ductility. A Vickers hardness of 10.95 GPa and a B/G ratio of approximately 1.93 corroborate these findings. Additional parameters, such as Poisson’s ratio, Debye temperature and average sound velocities, were derived to gain deeper insight into the material’s thermomechanical performance. These results provide a solid theoretical foundation for understanding the mechanical stability and potential anode suitability of V₃BO₆ in lithium-ion battery systems. Full article

The twist angle serves as a geometric tuning parameter in two-dimensional layered materials, enabling modulation of interlayer coupling and band structures without altering the chemical composition. In this work, six commensurate twisted bilayer WSe₂ configurations with rotation angles of 0°, 9.4°, 13.14°, 21.9°, 27.8°, and 60° were systematically investigated using first-principles density functional theory. Structural optimization, together with calculations of electronic structures, density of states, charge redistribution, effective masses, and optical properties, was performed. The results show that AA (0°) and 2H (60°) stackings exhibit the largest and smallest interlayer separations, respectively, whereas intermediate twist angles yield similar average spacings but distinct local stacking registries. All configurations remain indirect-gap semiconductors, with the valence band maximum located at K and the conduction band minimum near the Q point along the K–Γ path. The band gap increases from 1.450 eV at 0° to 1.579 eV at 27.8°, before decreasing to 1.333 eV at 60°, indicating strong twist-angle modulation of interlayer coupling. Density-of-states analysis shows that the valence-band edge mainly originates from Se-p and W-d hybridized states, whereas the conduction-band edge is dominated by W-d states, with intermediate angles exhibiting enhanced band folding and localization features. Charge-density analyses further reveal notable interfacial charge redistribution, which is most pronounced at 9.4°. Optical responses in the in-plane directions are nearly identical and significantly stronger than those along the out-of-plane direction. Optical absorption mainly occurs in the ultraviolet region, with band-edge features appearing in the near-infrared range. Intermediate twist angles exhibit broader dielectric responses in the visible region and extended long-wavelength tails, indicating enhanced interband transition channels. These results demonstrate that twist-angle engineering enables effective tuning of electronic and optical properties in bilayer WSe₂, providing theoretical guidance for the design of tunable optoelectronic devices. Full article

The precise control of non-metallic inclusions is crucial for high-end GCr15 bearing steel. This study investigates cerium (Ce)-induced inclusion modification mechanisms. Smelting experiments with 0 to 0.017 wt% Ce additions, high-temperature in situ observations, thermodynamics, and first-principles calculations were used to evaluate inclusion evolution and aggregation behaviors. Without Ce, coarse Al₂O₃ and MnS phases dominate. As Ce increases to 0.017 wt%, inclusions evolve sequentially into CeAlO₃, Ce₂O₃, and ultimately, finely dispersed Ce₂O₂S and CeS. Thermodynamics indicate CeAlO₃ nucleates preferentially, acting as heterogeneous nucleation sites for MnS. In situ observations and interparticle force calculations reveal an aggregation tendency order of Al₂O₃ > CeAlO₃ > Ce₂O₃ > Ce₂O₂S. Furthermore, first-principles simulations confirm that Ce₂O₂S possesses the lowest formation energy and optimal stability, wherein Ce effectively modifies coarse inclusions into fine, well-dispersed spherical particles. Coupled with its intrinsic deoxidizing and desulfurizing effects, Ce addition synergistically modifies coarse inclusions into fine, well-dispersed spherical particles. These findings elucidate the rare-earth modification micro-mechanisms, providing a theoretical foundation for manufacturing high-quality bearing steel. Full article

First-principles calculations are employed to systematically investigate the dynamic evolution from Al(O_h) to Al(T_d) in zeolites induced by proton–cation exchange (Cu⁺, Li⁺, Na⁺, NH₄⁺). The protons directly bonded to Al(O_h) are found to be essential for structural stability. Single cation exchange preserves the six-coordinated Al(O_h), while double exchange triggers spontaneous conversion to four-coordinated Al(T_d), accompanied by stepwise detachment of two water molecules. Different cations exhibit variations in spatial occupation patterns and water-binding strength. The coordination effect of metal cations and the hydrogen bonding effect of NH₄⁺ dominate the transformation of the aluminum coordination configurations. Protons directly bonded to Al(O_h) serve as strong Brønsted acid sites. Single exchange indirectly reduces the activity of adjacent protons, whereas double exchange eliminates Al–O–H bonds to stabilize Al(T_d). This work reveals a cooperative mechanism among cation species, exchange number, water binding, and electronic coupling that controls the Al(O_h) to Al(T_d) transformation, providing a theoretical basis for activating Al species and for designing high-performance catalysts with controlled acid site distributions via ion exchange. Full article

The hot-spot temperature in oil-immersed 3D wound core transformer has a significant impact on its performance. The complexity of the winding structure and the characteristics of oil flow increase the difficulty of temperature field analysis. To address this challenge, this study aims to propose a comprehensive thermal network model for oil-immersed 3D wound core transformers to accurately calculate the winding average temperature rise and local hot-spot temperature rise with high efficiency. First, based on the principle of constant thermal resistance, a detailed model of high- and low-voltage winding is calculated using 2D finite element simulation technology. An equivalent model is established to obtain the equivalent thermal conductivity. This model considers various variables, including wire diameter, external insulation dimensions, and the vertical and longitudinal spacing of the windings. Next, multiple types of thermal resistance are defined using the thermoelectric analogy method, and a global thermal network model of the oil-immersed 3D wound core transformer is constructed. Using the Gauss–Seidel method and relevant heat transfer theory, factors such as the flow of transformer cooling oil are taken into account, which allows for the calculation of the average temperature rise and local hot-spot temperature rise in the windings. This approach effectively reduces calculation time while ensuring accuracy. Finally, a 50 kVA oil-immersed amorphous alloy 3D wound core transformer is used as a case study, and temperature field experimental tests are conducted to verify the accuracy of the proposed analytical model. Full article

The structural, mechanical, electronic, and optical properties of cubic double perovskite oxides A₂TiSiO₆ (A = Ca, Sr, Ba) were systematically investigated using first-principles density functional theory calculations. Structural optimization within the GGA–PBE framework confirms that all compounds crystallize in a stable cubic phase. The negative formation energies indicate thermodynamic stability and potential experimental synthesizability. Ab initio molecular dynamics (AIMD) simulations performed at 300 K further confirm the dynamical stability of all compounds under finite-temperature conditions. The Born–Huang stability criteria performed elastic constant analysis establishes mechanical stability and the derived mechanical moduli indicate the presence of rigid but brittle behavior with moderate amounts of elastic anisotropy. Calculation of the electronic band structure reveals that all the compounds are direct wide-bandgap semiconductors, with the HSE06 bandgaps of Ca₂TiSiO₆, Sr₂TiSiO₆ as well as Ba₂TiSiO₆ being 2.61, 2.50 and 2.37 eV, respectively. The optical property analysis has shown that they are strong in terms of their absorption in the visible–ultraviolet region, with high dielectric constants and good refractive indices, which makes them appropriate in optoelectronics and photovoltaic applications. On the whole, A₂TiSiO₆ double perovskites are promising for use as wide-bandgap materials in the development of superior optoelectronic devices. Full article

Assessing carbon footprints has become increasingly important globally as a key tool for quantifying environmental impacts and supporting sustainable decision-making. However, although allegorical floats—central elements of large-scale parades in internationally recognized cultural festivals such as the Rose Parade in Pasadena, USA (RPP), the Rio de Janeiro Carnival, Brazil (RJC), the Black and White Carnival in San Juan de Pasto, Colombia (BWC), and the Fruit and Flower Festival in Ambato, Ecuador (FFF)—represent significant expressions of cultural heritage and artistic creativity, their environmental impact has received limited attention in sustainability research. The primary objective was to quantify the carbon emissions associated with constructing these temporary structures. The methodology integrated geometric surface estimation with carbon accounting principles commonly applied in life-cycle assessment. Emissions were calculated based on the material composition of the structural, covering, and finishing stages, and normalized using two indicators: kilograms of CO₂ equivalent (kg CO₂e) per square meter of float surface area and kg CO₂e per float. Results indicate that emission intensity varies substantially across festivals, with RJC exhibiting the highest value (approximately 9 kg CO₂e/m²) due to extensive use of synthetic materials, while BWC demonstrates the lowest intensity (approximately 4.3 kg CO₂e/m²) as a result of greater reliance on wood- and paper-based components. When assessed per float, the large scale of RJC structures leads to emissions exceeding 30,000 kg CO₂e per float, whereas FFF floats generate less than 1000 kg CO₂e due to their smaller dimensions and use of natural materials. This research constitutes the first comparative carbon assessment of allegorical float construction and advances the emerging intersection of cultural heritage studies and environmental sustainability. Full article

The structural and magnetic properties and band structure results of HoCo_3−xSi_x compounds are reported. First-principles GGA+U+SO calculations, compared with magnetometry experiments, provide deep insight on the magnetic properties of the HoCo₃ compound. They show that HoCo₃ is a robust ferrimagnet, with strongly localized Ho-4f moments in excellent agreement with neutron data and itinerant Co-3d magnetism, where inclusion of the interstitial contribution brings the Co moments into very good agreement with the experimental data. The electronic structure reveals sharp Ho-4f states well below E_F, exchange-split Co-3d bands crossing E_F, and noticeable Ho-5d–Co-3d hybridization that mediates the antiparallel Ho–Co coupling and explains the non-negligible interstitial moment, providing a consistent microscopic picture that supports the experimentally observed increase in magnetization upon Co-Si substitution. Metamagnetic transitions are shown in magnetization isotherms. The observed transitions are broad and can be explained by the distribution of internal magnetic fields which arises from differences in the local environments of cobalt atoms. The magnetic properties were correlated with the theoretical results. Two transitions were revealed below room temperature, one due to a transition to a noncollinear magnetic structure and the other due to a temperature-induced metamagnetic transition. Full article

O3-type layered transition-metal oxides are widely regarded as promising cathode materials for sodium-ion batteries due to their intrinsically high sodium content and favorable energy density. Nevertheless, their practical rate capability is hindered by sluggish Na⁺ transport and relatively high diffusion barriers. To address this issue, elemental substitution has emerged as an effective modification strategy. In this work, fluorine (F), characterized by strong electronegativity and a small ionic radius, is introduced to partially substitute oxygen in the bulk lattice of O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NNFM). First-principles calculations demonstrate that F incorporation leads to an expansion of the interlayer spacing along the c-axis and a weakening of Na–O interactions, both of which facilitate Na⁺ migration. Among the considered configurations, Mn-adjacent substitution exhibits the lowest formation energy, indicating enhanced thermodynamic stability. Furthermore, electronic structure analysis reveals a reduced band gap (from 0.515 eV to 0.342–0.356 eV) and strengthened O-2p/Mn-3d orbital hybridization, contributing to improved electronic conductivity. These findings provide atomistic insights into F-induced modulation mechanisms and suggest an effective pathway for optimizing Na⁺ transport in O3-type cathodes. Full article

Oxygen stoichiometry critically governs the phase stability and physical properties of transition-metal oxides, yet a unified understanding of how oxygen-stoichiometry-driven phase reconstruction underlies the cooperative evolution of multiple physical properties in SrCoO_x remains lacking. Here, high-quality epitaxial brown millerite SrCoO_2.5 and perovskite SrCoO_3−δ thin films were grown by pulsed laser deposition under controlled oxygen conditions. Their structural, magnetic, electrical, optical, and photocatalytic properties were systematically compared. SrCoO_2.5 exhibits antiferromagnetic insulating behavior, infrared-dominant transmittance, and higher photocatalytic activity, whereas SrCoO_3−δ shows ferromagnetism, much lower resistivity, and strong optical opacity. First-principles calculations reveal that oxygen-stoichiometry-driven phase reconstruction strongly modifies the electronic structure, accounting for the distinct magnetic, transport, and optical responses. These results establish a direct correlation between oxygen stoichiometry, structural transformation, and multifunctional properties in SrCoO_x, highlighting oxygen-vacancy ordering as an effective route to tailoring correlated oxide functionalities. Full article

The dielectric response provides an integral description of polarization mechanisms across frequency ranges and constitutes a key physical basis for understanding ferroelectric behavior. Here, we systematically investigate the broadband dielectric response of Group-II metal oxide (BeO, MgO, CaO, ZnO, and CdO) monolayers using first-principles calculation. In the low-frequency regime, ionic polarization governs the dielectric response. A distinctive feature is the LO–TO degeneracy at the Γ point accompanied by a V-shaped nonanalytic LO phonon dispersion. d-state hybridization increases with the metal atomic number, resulting in higher Born effective charge, which works together with phonon softening, reduced mass and unit cell area to significantly strengthen the ionic dielectric contribution. The quasiparticle band gap decreases with the metal atomic number, driving redshifts of the dielectric function and wide band optical response from the deep-ultraviolet to the near-infrared. Particularly, CdO exhibits the strongest electronic polarization, with an optical dielectric constant of 2.68 and a static refractive index of 1.64. This work establishes a complete dielectric spectrum from ionic to electronic polarization, providing theoretical guidance for polarization engineering and design of two-dimensional ferroelectric devices. Full article

Designing stable and multifunctional perovskite materials with tunable electronic and optical properties is crucial for advancing next-generation optoelectronic and high-temperature applications. In this study, the structural, electronic, optical, mechanical, and thermal properties of XYO₃ (X = Nb, Ta; Y = Ag, Au) cubic perovskites were systematically investigated using density functional theory (DFT). Each compound crystallized into a cubic perovskite structure and was found to be both thermodynamically and dynamically stable. Hybrid functional (HSE06) calculations indicate semiconducting behavior with band gaps of 1.885 eV (NbAgO₃), 1.298 eV (NbAuO₃), 3.074 eV (TaAgO₃), and 1.801 eV (TaAuO₃). The density-of-state analysis reveals strong hybridization between the O-2p and Nb/Ta-d orbitals, which hints at mixed ionic/covalent bonding. Optical properties exhibit large absorption coefficients (about 10⁶ cm⁻¹) in the ultraviolet range and at lower reflectivity, especially of NbAgO₃ and TaAgO₃, indicating efficient light absorption. NbAgO₃ and NbAuO₃ possess moderate direct band gaps, making them suitable for optoelectronic and photovoltaic applications, whereas the wide bandgap of TaAgO₃ is beneficial in ultraviolet optoelectronic devices. Mechanical analysis confirms the ductile nature of all compounds, with TaAuO₃ exhibiting the highest ductility. Thermal analysis indicates that NbAgO₃ and TaAgO₃ exhibit higher lattice rigidity and thermal conductivity, but NbAuO₃ and TaAuO₃ are more anharmonic and have higher thermal expansion. Overall, these results demonstrate the multifunctional potential of XYO₃ perovskites for applications in optoelectronics, photovoltaics, ultraviolet devices, flexible electronics, and high-temperature environments. Full article