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Coupling Weyl quasiparticles and charge density waves (CDWs) can lead to fascinating band renormalization and many-body effects beyond band folding and Peierls gaps. For the quasi-one-dimensional chiral compound (TaSe4)2I with an incommensurate CDW transition at TC = 263 K, photoemission mappings thus far are intriguing due to suppressed emission near the Fermi level. Models for this unconventional behavior include axion insulator phases, correlation pseudogaps, polaron subbands, bipolaron bound states, etc. Our photoemission measurements show sharp quasiparticle bands crossing the Fermi level at T > TC, but for T < TC, these bands retain their dispersions with no Peierls or axion gaps at the Weyl points. Instead, occupied band edges recede from the Fermi level, opening a spectral gap. Our results confirm localization of quasiparticles (holes created by photoemission) is the key physics, which suppresses spectral weights over an energy window governed by incommensurate modulation and inherent phase defects of CDW.

We incorporate Se into the 3D halide perovskite framework using the zwitterionic ligand: SeCYS (+NH3(CH2)2Se-), which occupies both the X- and A+ sites in the prototypical ABX3 perovskite. The new organoselenide-halide perovskites: (SeCYS)PbX2 (X=Cl, Br) expand upon the recently discovered organosulfide-halide perovskites. Single-crystal X-ray diffraction and pair distribution function analysis reveal the average structures of the organoselenide-halide perovskites, whereas the local lead coordination environments and their distributions were probed through solid-state 77Se and 207Pb NMR, complemented by theoretical simulations. Density functional theory calculations illustrate that the band structures of (SeCYS)PbX2 largely resemble those of their S analogs, with similar band dispersion patterns, yet with a considerable band gap decrease. Optical absorbance measurements indeed show band gaps of 2.07 and 1.86 eV for (SeCYS)PbX2 with X=Cl and Br, respectively. We further demonstrate routes to alloying the halides (Cl, Br) and chalcogenides (S, Se) continuously tuning the band gap from 1.86 to 2.31 eV-straddling the ideal range for tandem solar cells or visible-light photocatalysis. The comprehensive description of the average and local structures, and how they can fine-tune the band gap and potential trap states, respectively, establishes the foundation for understanding this new perovskite family, which combines solid-state and organo-main-group chemistry.

The phosphors for pc-LEDs have high thermal stability requirements due to the high operating temperature of LEDs. In addition, there are many phosphors based on SrNb 2 O 6 , but no one has studied Sm3+ or Tb3+ as the luminescent center of SrNb 2 O 6 host. Therefore, two new phosphors based on SrNb 2 O 6 host are proposed in this work. One is an orange phosphor with negative thermal quenching phenomenon using Sm3+ as the luminescent center, and the other is a green phosphor with Tb3+ as the luminescent center. In this work, a series of SrNb 2 O 6 :Sm3+ and SrNb 2 O 6 :Tb3+ phosphors were prepared by the solid-state reaction method. The structure, morphology, chemical composition, absorption properties and luminescence properties of Sm3+ and Tb3+ doped SrNb 2 O 6 samples were studied. Under 405 nm excitation, the SrNb 2 O 6 :Sm3+ samples exhibit the 4f-4f transition of Sm3+ with the strongest emission intensity at 607 nm, the emission intensity of SrNb 2 O 6 :0.03Sm3+ phosphor at 150 °C remains at 100.56% of its room temperature value and the chromaticity coordinates are located in the orange region, with a color purity of 88.19%. Under 307 nm excitation, the SrNb 2 O 6 :Tb3+ samples exhibit the 4f-4f transition of Tb3+ with the strongest emission intensity at 544 nm, the emission intensity of SrNb 2 O 6 :0.09Tb3+ phosphor at 150 °C remains at 7.68% of its room temperature value and the chromaticity coordinates are located in the green region with a color purity of 74.29%. Additionally, Na+ is introduced as a charge compensator in the Sm3+ or Tb3+ doped phosphors, which enhances their luminescence intensity. These results indicate that the two phosphors synthesized in this work have the prospect of application in the field of solid-state lighting. [ABSTRACT FROM AUTHOR]

Based on density functional theory (DFT), a two-dimensional(2D) metal-organic framework (MOF) based on Co and Cu atoms were presented. Based on the phonon dispersion calculations, no imaginary mode is found in the phonon branches, which verifies that the crystal structures of MOF could be stable. Based on the calculation of electronic band structure, it is found that the Cu-based MOF is a metallic system by applying external electric field. While the Co-based MOF undergoes a transition from metal to semiconductor under external electric field. When the external electric field intensity reaches up to 0. 5 eV/Å, the band gap of Co-based MOF is around 0. 1 eV, while this does not happen in the Cu-based MOF. Furthermore, the N2 adsorption and the nitrogen reduction reaction (NRR) were investigated for the Co-based MOF, which shows that the NRR for the Co-based MOF exhibits good performance, and the electric field could enhance this effect of NRR. The free energy of NRR under external electric field of 0. 5 eV/Å is 0. 51 eV lower than that without electric field. Therefore, our study would prospectively guide the experimental researchers on the design of NRR. [ABSTRACT FROM AUTHOR]

Pb‐free perovskites are novel compounds that are currently being studied, essentially for their photovoltaic applications. In this article, the hybrid organic–inorganic perovskite for photovoltaic applications is studied. In fact, the structural and electronic properties of the perovskite FABI3 (B = Sn, Ge, or Pb and FA = formamidinium: CH(NH2)2) applying the density functional theory method executed in the Quantum Espresso framework are studied and discussed. The band structures of these perovskites have been presented; it is shown that these perovskites have a semiconductor nature, with a bandgap value of 1.36 eV for FASnI3, 1.72 eV for FAGeI3, and 1.61 eV for FAPbI3. Also, the density of states and partial density of states have been presented and discussed for each of these materials. Indeed, the structural properties of these perovskites are investigated and demonstrated that the optimized value of the lattice parameter is 6.35 Å for the FASnI3, while for the FAGeI3, this value is 6.3 Å and 6.5 Å for FAPbI3. Moreover, the impact of the lattice parameter on the bandgap value of FABI3 (B = Sn, Ge, or Pb) has been investigated, and it has been demonstrated that as the lattice parameter increases, the bandgap increases. The results of this work can be utilized as a guideline for the development of new efficient, lead‐free perovskite devices, including tandem solar cells. [ABSTRACT FROM AUTHOR]

Understanding the properties of lithium vacancy, LiCV, defects in diamond is crucial for optimizing diamond-based semiconductor performance and unlocking its full potential in advanced electronic applications. In this study, we present a comprehensive theoretical investigation of the neutral LiCV defect, resulting from the interaction between a lithium substitutional and a vacancy, in diamond. Employing periodic supercell calculations, we utilize global (B3LYP and PBE0) and range-separated (HSE06) hybrid functionals, as well as a local basis set, within the CRYSTAL17 code to analyze the relaxed lattice structure, formation energy, magnetic properties, and electronic structures of LiCV and other related isolated defects (LiC V and 2V). Our results reveal that LiCV exhibits three distinct spin states (doublet, quartet, and sextet) with significant differences in spin density distributions on first-neighbor carbon atoms. The quartet state is energetically favored by 0.09 eV and 0.88 eV (B3LYP) compared to the doublet and sextet states, respectively. The Li atom is positioned midway between the two vacancies in the LiCV defect, exhibiting a local D3d symmetry. Our findings reveal that the LiCV defect exhibits remarkable stability within the diamond matrix, with its dissociation into LiC and a vacancy (V) demanding a substantial energy barrier of 6.07 eV. In environments rich in vacancies, LiC shows a strong preference for binding with these vacancies, thereby facilitating the formation of LiCV complexes. Raman scattering calculations offer intriguing insights into the LiCV defect, revealing distinctive spectral features that significantly aid in distinguishing this particular defect among isolated lithium LiC and vacancy (V) defects. This observation is crucial, especially considering the challenges in fabricating shallow donors involving interstitial lithium in diamond, where preexisting vacancies can significantly influence the process. The comprehensive analysis provided in this study not only deepens our understanding of the LiCV defect and its physical properties but also enhances our ability to detect this defect during the synthetic process, and to precisely control the formation conditions. This capability is vital for optimizing the electronic properties of diamond for advanced technological applications. [ABSTRACT FROM AUTHOR]

Hydrogen evolution reaction (HER) from seawater electrolysis still faces challenges of low reactivity and chloride ions poison at the active sites, leading to reduced efficiency and stability of electrocatalysts. This study presents edge dislocation strategy aimed at inducing lattice strain in ferric oxide through Mo doping, consequently regulating the catalyst's band structure. Through in situ characterizations and DFT analysis, it is confirmed that lattice strain effectively modulates the band structure, intensifies the hybridization between Mo(d)‐Fe(d)‐O(p) orbitals, thereby accelerating the charge transfer rate of HER. Furthermore, band structure modulated by lattice strain enhances water adsorption capacity, reduces the adsorption energy of Cl−, and optimizes the hydrogen adsorption‐free energy (ΔGH*) for HER. Benefiting from above, the optimized 2%‐Mo‐Fe2O3 catalyst demonstrates HER activity and stability in alkaline seawater electrolysis comparable to that of commercial Pt/C. Additionally, the assembled electrolytic cell utilizing an anion exchange membrane (AEM) maintains long‐term stability for >100 h at 500 mA cm−2, showcasing a sustained catalytic effect. [ABSTRACT FROM AUTHOR]

Acoustic topological insulators have the excellent characteristic of the pseudospin-dependent one-way transmission of sound edge states immune to backscattering. We realize the broadband acoustic pseudospin topological edge states with subwavelength generalized topological insulators, which is achieved by reverse pseudospin-orbit coupling. The subwavelength band and broadband nontrivial bandgap can be achieved by adjusting the topological structure of the scatterers and introducing resonators. The results demonstrate that the resonator can significantly reduce the frequencies of p-states and dstates by introducing resonance scattering; the scattering size and rotation angles change the frequencies of p-states and d-states in opposite directions by adjusting the distribution of the sound field. Then, we experimentally realize the pseudospin-dependent one-way transmission of sound edge states along the interface separating phononic crystals with distinct topological phases. Our research provides a systematic scheme for the design of acoustic topological insulators with versatile applications. [ABSTRACT FROM AUTHOR]

Strain engineering serves as an effective method for optimizing electronic and optical properties in semiconductor devices, with applications including the enhancement of optical emission in Ge and GeSn‐based devices, improvement of carrier mobility, and second harmonic generation in silicon photonics structures. Current methods for deformation characterization in semiconductors, such as X‐ray diffraction and Raman spectroscopy, often require bulky and expensive setups and are limited in vertical resolution. Consequently, techniques capable of measuring lattice strain while overcoming these drawbacks are highly desirable. This study proposes a proof of concept for a cost‐effective, compact, fast, and non‐destructive approach to probe non‐uniform strain fields and additional material properties by exploiting the bulk photovoltage effect. The method is benchmarked with an array of silicon nitride stripes deposited under varying pressure conditions on a germanium substrate. Initially, their surface strains are verified through Raman spectroscopy. The deformations are replicated in a finite element method platform by integrating mechanical simulations with deformation potential theory, thereby estimating the band edge energy landscape. Finally, the study discusses the theoretical behavior of the photovoltage signal, considering semiconductor properties, defects, doping, and deformation. The findings offer insights into the development of advanced techniques for strain and transport analysis in semiconductor materials. [ABSTRACT FROM AUTHOR]

In this paper, the structure and electronic properties of InP/PtS 2 heterojunction as well as the photocatalytic and solar hydrogen production efficiency are studied by first principles. Studies have shown that InP/PtS 2 heterojunction is type II band alignment, typical Z heterostructure, has strong light absorption coefficient in the absorption spectrumand, InP/PtS 2 heterojunction with an indirect bandgap of 1.97 eV，the band edge positions that meet the energy band prerequisites for water splitting across different pH levels，The band edge positions and light absorption capabilities have been modified through biaxial strain, with tensile strain enhancing the absorption capacity within the visible light spectrum ranging from 450 to 800 nm(nm). The InP/PtS 2 heterojunction achieves a solar-to-hydrogen conversion efficiency (ηSTH) of 32.5%, which is higher than that of most heterojunctions. The InP/PtS 2 heterojunction is anticipated to emerge as a promising contender for the next generation of photocatalysts. InP/PtS 2 heterojunction is a typical direct Z-scheme heterojunction, which can change its electronic and optical properties under strain, and may contribute to the fields of water splitting. The solar-to-hydrogen efficiency of the InP/PtS2 heterostructure can reached 32.5%. The absorption coefficient in the visible range is enhanced by the application of strain. [Display omitted] • Compared with InP monolayer and PtS 2 monolayer, InP/PtS 2 heterojunctions have better visible light absorption efficiency. • The InP/PtS 2 heterojunction achieves a solar-to-hydrogen conversion efficiency (ηSTH) of 32.5%, which is higher than that of most heterojunctions. [ABSTRACT FROM AUTHOR]

The structural stability, electronic structure, and optical properties of the novel YxGd1-xN ternary alloys were studied using the FP-LAPW method with the generalized gradient approximation + Hubbard U (GGA + U). Our results reveal that YxGd1-xN alloys can be experimentally synthesized because they exhibit energetic and mechanical stability. All these systems present semiconducting behavior. Both GdN and YN are indirect band gap semiconductors while YxGd1-xN alloys are direct band gap semiconductors for $x = 0.25\comma \; 0.5\comma \; 0.75$ x = 0.25 , 0.5 , 0.75 because of hybridization between d (Y) and Gd(f) orbitals in the vicinity of the Fermi energy level. The f-d coupling induces the major magnetic moments on the Gd atom. The absorption spectra are reasonably high (>105 cm−1) and the bandgap energy and structure spacing match between YN and GaN which made YxGd1-xN alloys suitable for optoelectronic applications. In the absence of experimental work, our results can be useful for further studies. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive investigation into the electronic properties of Hydroxyapatite (HAp) doped with Zinc (Zn) and Cobalt (Co). Five distinct compositions, denoted as 0.15Zn-HAp, 0.15Co-0.15Zn-HAp, 0.30Co-0.15Zn-HAp, 0.45Co-0.15Zn-HAp, and 0.6Co-0.15Zn-HAp (at%,) have been systematically studied employing Density of States (DOS) and band structure calculations. The computed band gap values for these compositions were determined to be 4.6663, 4.6888, 4.7049, 4.7159, and 4.7082 eV, respectively. These results illuminate the profound influence of Zn and Co doping on the electronic structure of Hydroxyapatite. These findings hold significant implications for the potential applications of these materials in diverse technological and biomedical domains. The systematic approach and precise electronic property characterizations presented in this study provide a robust foundation for further advancements in the realm of advanced materials, with particular relevance to the development of innovative materials for use in cutting-edge technologies and medical applications. [ABSTRACT FROM AUTHOR]

This study is aimed to investigate the effects of introducing dysprosium (Dy) into Zn-based hydroxyapatite (HAp) at various concentrations (0.45, 0.90, 1.35 and 1.80%). The structural and optical properties of pure and doped HAp were thoroughly examined through theoretical and empirical analyses, including X-ray diffraction, Raman spectroscopy and Fourier transform infrared (FTIR) studies. The results confirmed the successful incorporation of Dy into the HAp lattice without significantly affecting its thermal stability or stoichiometry. The introduction of Dy into Zn-based HAp led to notable alterations in several material parameters. The lattice parameters, crystallinity, lattice stress, strain and anisotropic energy density varied with different Dy concentrations. In comparison with undoped HAp, all Dy-doped Zn-based HAps exhibited reduced crystallite size values, indicating a change in the microstructure. Furthermore, the material density increased from 3.159 to 3.228 g cm−3 with Dy doping. The band gap (BG), an important parameter for optical applications, is consistently decreased from 4.6 to 3.9 eV as the Dy concentration increased. This decrease in BG suggests the potential for improved photocatalytic or optoelectronic properties in Dy-doped Zn-based HAp. Additionally, the linear absorption coefficient (LAC) increased, indicating enhanced light absorption. Overall, this study provides a comprehensive understanding of structural and optical modifications induced by Dy doping in Zn-based HAp. These findings contribute to the potential application of Dy-doped Zn-based HAp in various fields, including biomedicine, photocatalysis and optoelectronics. [ABSTRACT FROM AUTHOR]

In this paper, electronic properties of Janus MSX monolayers (M = Mo, W; X = Se or Te), including electron energy loss near edge structures (ELNES), as K and L2,3 edge spectra of sulfur atoms, have been calculated using a full potential scheme and the augmented plane wave plus local orbitals (APW+lo) method in the framework of density functional theory (DFT). Due to the lack of experimental results, the obtained spectra are compared with the corresponding spectra of MoS2 monolayer. The band structure analysis shows that the Janus MoSSe and WSSe monolayers are direct bandgap semiconductors, while the Janus MoSTe and WSTe monolayers are indirect bandgap semiconductors. In comparison to MoS2, the main structures of the K edge ELNES spectra of sulfur atoms in Janus monolayers occur at lower energies, due to the structural change and increased bond length. The relative reduction of intensities in the main structures predicts the possibility of reducing the number of partial densities of states (PDOS), that is, the reduced p PDOS for the K edge in the corresponding energy range. In the K (L2,3) edge ELNES spectra of the sulfur atom in Janus monolayers and MoS2 monolayers, the main structures are due to the electron transfer to the unoccupied px+py and pz states (3s of sulfur and 4d states of the transition metal). [ABSTRACT FROM AUTHOR]

The theoretical expectation of semi‐polar light emitting diodes (LEDs) is reviewed and compared it to the experimental data. The reported peak internal quantum efficiency (IQE) of non‐polar, and semi‐polar InGaN LEDs are always much lower than the standard polar (0001) oriented LEDs. Calculating the band structure and states including the n‐ and p‐doped layer of LEDs in many orientations, It is found that the inverted polarization‐induced fields for most common semi‐polar orientations like (112¯$\bar{2}$2) or (202¯${\bar{2}}$1) causes the hole ground state to leak out of the quantum well (QW) into the p‐doped GaN above and by this a low wavefunction overlap and a strongly increased probability for non‐radiative recombination with point defect outside the QW. Based on the calculations, (112¯$\bar{2}$1), (101¯$\bar{1}$2), or (101¯$\bar{1}$3) are predicted as best candidates for LEDs with higher IQE at higher current densities than (0001). LEDs in the uncommon semi‐polar (101¯$\bar{1}$3) orientation on sapphire have been realized. The (101¯$\bar{1}$3) LEDs showed the same IQE as (0001) LEDs but at a much higher current density due to the higher overlap of electron and hole wave functions, which is especially useful for micro‐LEDs. [ABSTRACT FROM AUTHOR]

Using density functional theory and Boltzmann equations, this study calculates and compares the electronic, optical, thermoelectric, and thermodynamic properties of bulk and single-layer germanium carbide structures. It has been shown that germanium carbide in the bulk structure has an indirect energy band gap of 1.61 eV. In a single layer structure, it is a metal. Thermodynamic properties including specific heat at constant volume have been investigated using the quasi-harmonic approximation (QHA) package in QE. According to the studies conducted on optical properties, this material shows good reflection in the visible region. In addition, this structure has high electrical conductivity and low thermal conductivity, which is essential for thermoelectric materials. Thermoelectric calculations using semi-classical Boltzmann transfer theory show that the performance of two-dimensional compounds with graphene gives good thermoelectric results. At 100 K, the highest figure of merit (ZT) for GeC is 1.00. Our findings evaluate the GeC compound as a suitable thermoelectric material in the temperature gradient from 100 to 900 K. [ABSTRACT FROM AUTHOR]

The interaction of H, H2, and MgH2 with graphene is investigated using the density functional theory to explore the possibility of exploiting graphene or functionalized graphene as a hydrogen storage medium. The H atom is positioned at various distances from the graphene surface and the energetics are computed in detail. The extent of interaction of the s electron of H with graphene's pz electrons is well brought out. Similar investigations are carried out for H2, MgH2. In the case of H atom, a HC covalent bond is formed. This process turns out to be a prerequisite for proton transfer through graphene. Interactions of H2 and MgH2 with graphene are different from that of H. It leads to the conclusion that functionalized graphene will better substrate/candidate for applications like hydrogen storage. [ABSTRACT FROM AUTHOR]

Zintl materials have received enormous attention in recent time due to their unique structure and thermoelectric efficiency. In this work, quaternary Zintl compounds LaAgZnX2 (X = P, As) have been comprehensively investigated using the FP-LAPW + lo method through first principles approximation. The dynamic stability of the samples is performed through phonon analysis. Birch–Murnaghan equation of states is used to determine ground state parameters. The lattice constant increases while formation energy and bulk modulus B(GPa) decrease by anion replacement from P to As. Band structure calculation shows that LaAgZnP2 is an indirect bandgap semiconductor while LaAgZnAs2 is a direct bandgap semiconductor. The density of states (DOS) demonstrates that the valence band (V.B) is mainly comprised of Zn-d and X-p states while the La-f state is in the conduction band (C.B) along with the minor contribution of the La-d state. Substantial absorption is observed in the low-frequency ultraviolet and visible spectrums for these compounds. Red shifting of the hallmark optic peak occurs due to the anion replacement from P to As. To investigate the electric and thermal conductivities, Seebeck coefficients, and thermopower factor, the Boltzmann transport theory is used to quantify them for these materials. High absorption peaks and figures of merits of these compounds highlight their potential usage in optoelectronics and thermoelectric systems. [ABSTRACT FROM AUTHOR]

The comprehensive first-principles analysis of Ba4Sb4Se11 and [Ba4Sb4Se11]:Sr3+ Selenoantimonate Using DFT demonstrates its semiconductor nature, anisotropic ductile properties, and prospective optoelectronic applications, particularly in solar cells and LED technologies, supported by comprehensive structural, electronic, optical, and mechanical studies. All the relevant parameters were determined in this investigation using the framework of DFT by modified Becke Johnson approximations. These parameters include the extinction coefficient, absorption coefficient, energy loss function, reflectivity, refractive index, optical conductivity, and birefringes. The elastic parameters have been calculated based on anisotropic sound velocities and mechanical stability. These parameters include bulk modulus, shear modulus, Young's modulus, and Poisson's ratio. Based on an analysis of the energy band dispersions, it can be concluded that the examined compounds possess semiconductor properties. The data on elastic parameters suggest that the material exhibits anisotropic and ductile characteristics, which could have potential applications in optoelectronics. The Ba4Sb4Se11 (2.2 eV) and [Ba4Sb4Se11]: Sr3+ (1.68 eV) have a direct band gap, which falls within the visible spectrum showing semiconducting nature. The analysis of the thermoelectric properties of investigated compounds has been conducted using the Boltztrap code, marking a significant in scientific research. The study revealed that these compounds have the potential to be utilized in highly challenging transport conditions. Additional investigations and cooperation are essential for understanding the fundamental processes and enhancing the material for effective utilization in various technological applications for solar cells and LED in the energy and optoelectronic industry. [ABSTRACT FROM AUTHOR]

A series of Cu12-xGaxSb4S13 (x=0,0.05,0.1 and 0.15) samples were synthesized through high-temperature melting method and heat annealing technique combined with spark plasma sintering (SPS). The phase composition, band structure and thermoelectric properties of the samples were characterized and analyzed. The results show that Ga doping can introduce impurity band near the conduction band, acting as donor energy level, thus reducing the hole carrier concentration and increasing the Seebeck coefficient of the samples. At the same time, with the increase of Ga doping content, the thermal conductivity of Ga-doped samples decreases significantly. When the temperature is 770 K, the thermal conductivity of Cu11.85Ga0.15Sb4S13 sample decreases to 1.20 W/mK, which is 29% lower than that of the intrinsic material. Finally, the maximum ZT value of 0.7 is achieved for Cu11.9Ga0.1Sb4S13 sample at 770 K, a 40% improvement over the intrinsic Cu12Sb4S13. [ABSTRACT FROM AUTHOR]

Aiming to efficiently expedite alkaline overall water splitting (OWS) by addressing challenges such as sluggish kinetics and limited stability, a hollow Fe‐doped Ni(OH)2‐NiS@Ni(OH)2 nanorod array with surface nanosheets is devised, featuring a high‐index Fe‐doped Ni(OH)2(101)‐NiS(211) heterostructural interface and an upshifted d‐band center. This nanoarchitecture intensifies the adsorption and interaction of H2O and OH− reactants on the electrocatalyst surface, suitably bonds the *H intermediate in hydrogen evolution reaction (HER) and accelerates electron movement of *H, minimizes the energy requirement of the rate‐limiting phase (*OH → *O) in oxygen evolution reaction (OER) by facilitating O─H cleavage of *OH and optimally adsorbs *O, amplifies the exposure of surface‐active centers, and ultimately reduces the apparent activation energy. Consequently, the overpotentials are as low as 66.4 mV (HER) and 254.9 mV (OER) at 10 mA cm−2, alongside high turnover frequencies of 142 s−1 (H2) and 279 s−1 (O2) at 100 and 300 mV, respectively, markedly outperforming direct‐electrodeposited analogues. When functioning as a bifunctional electrode in OWS, this material merely requires 1.57 V at 10 mA cm−2 and sustains an operation for 168 h, approaching Pt/C||RuO2 benchmark. [ABSTRACT FROM AUTHOR]

The magnetic properties, band structure results, and magnetocaloric effect of GdCo1.8M0.2 with M = Fe, Mn, Cu, and Al are reported. The band structure calculations demonstrate that all the samples have a ferrimagnetically ordered ground state, in perfect agreement with the magnetic measurements. Calculated magnetic moments and variation with the alloy composition are strongly influenced by hybridisation mechanisms as sustained by an analysis of the orbital projected local density of states. The XPS measurements reveal no significant shift in the binding energy of the investigated Co core levels with a change in the dopant element. The Co 3s core-level spectra gave us direct evidence of the local magnetic moments on Co sites and an average magnetic moment of 1.3 µB/atom was found, being in good agreement with the theoretical estimation and magnetic measurements. From the Mn 3s core-level spectra, a value of 2.1 µB/Mn was obtained. The symmetric shapes of magnetic entropy changes, the Arrott plots, and the temperature dependence of Landau coefficients clearly indicate a second-order phase transition. The relative cooling power, RCP(S), normalized relative cooling power, RCP(∆S)/∆B, and temperature-averaged entropy change values indicate that these compounds could be promising candidates for applications in magnetic refrigeration devices. [ABSTRACT FROM AUTHOR]

As a most promising environmental technology, the substantial enhancement of photocatalytic efficiency is still a big challenge for practical applications. In this work, the surface of Bi2O2CO3 (BOC) nanotubes are modified by Cl and I. The as-obtained samples at different hydrothermal temperatures (T) are designated as T-X-BOC (X = Cl, I). X-ray diffraction (XRD), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS) prove that Cl and I merely chemically adsorb on the BOC surface, rather than dope into the crystal lattice. The surface modification of Cl and I slightly increases light absorption range, while significantly promotes the photoelectron migration from bulk to the surface that greatly enhances the carrier separation efficiency. Density functional theory (DFT) calculations further prove that surface Cl and I have adjusted band structure and surface charge distribution. Besides, the surface Cl and I favor the O2 adsorption and trap the surface photoelectrons, thus promoting the formation of •O2–; while the surface Cl and I impede the surface adsorption of H2O, thus refraining the generation of •OH. In the degradation of rhodamine B (RhB), holes and •O2− radicals play the crucial role. Under ultraviolet light irradiation (λ < 420 nm) for 45 min, the RhB degradation ratios over 150-Cl-BOC (94%) and 150-I-BOC (85%) are 4.2 and 3.7 times higher than that of original BOC (18%), respectively. This work demonstrates that the simple surface halogenation modification greatly improves the photocatalytic activity. [ABSTRACT FROM AUTHOR]

In this study, cerium dioxide (CeO 2) materials doped with one (Gd3+, GDC), two (Gd3+ and Na+, GNDC), and three (Gd3+, Na+, and Eu3+, EGNDC) components were, respectively, prepared, and their high-temperature infrared emissivity was investigated through experimental measurements and theoretical calculations. The experimental results show that GDC exhibits the highest oxygen vacancy concentration, highest conductivity, and narrowest band gap; furthermore, it exhibits an ultralow infrared emissivity (0.202 at 600 °C). The band structure calculations reveal that the Fermi level of GDC shows the highest total density of states, and electrons are more likely to enter the conduction band, which increases the conductivity and thus reduces the infrared emissivity. Furthermore, the infrared reflectance decreases gradually with increasing number of doping components, and the highest infrared reflectance and lowest infrared emissivity for GDC are obtained at 3–5 μm. These findings are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Quaternary chalcogenide compositions have gained much attention because of their promising potential for various optoelectronic applications. The band structure, density of states, and optical properties of CuZn2InS4 and CuZn2GaS4 for kesterite and stannite structures are studied with the full-potential augmented plane wave method as implemented in the Wien2k code. The total energy in equilibrium is calculated for different possible crystal structures. The phase stability and transitions with p–d orbitals are also analyzed. Moreover, the absorption coefficient, dielectric function, and refractive index of these materials are explored within a broad range of energy. We compare the calculated band gap values with available experimental results. [ABSTRACT FROM AUTHOR]

Abstract Exploration of metastable phases holds profound implications for functional materials. Herein, we engineer the metastable phase to enhance the thermoelectric performance of germanium selenide (GeSe) through tailoring the chemical bonding mechanism. Initially, AgInTe2 alloying fosters a transition from stable orthorhombic to metastable rhombohedral phase in GeSe by substantially promoting p‐state electron bonding to form metavalent bonding (MVB). Besides, extra Pb is employed to prevent a transition into a stable hexagonal phase at elevated temperatures by moderately enhancing the degree of MVB. The stabilization of the metastable rhombohedral phase generates an optimized bandgap, sharpened valence band edge, and stimulative band convergence compared to stable phases. This leads to decent carrier concentration, improved carrier mobility, and enhanced density‐of‐state effective mass, culminating in a superior power factor. Moreover, lattice thermal conductivity is suppressed by pronounced lattice anharmonicity, low sound velocity, and strong phonon scattering induced by multiple defects. Consequently, a maximum zT of 1.0 at 773 K is achieved in (Ge0.98Pb0.02Se)0.875(AgInTe2)0.125, resulting in a maximum energy conversion efficiency of 4.90% under the temperature difference of 500 K. This work underscores the significance of regulating MVB to stabilize metastable phases in chalcogenides.

Zintl compounds such as n‐type Mg3(Sb,Bi)2 show promising thermoelectric applications benefiting from their high valley degeneracy and low lattice thermal conductivity. However, the heavier p‐type AMg2X2 (A = Ca, and Yb; X = Bi and Sb) Zintl counterparts even exhibit a higher κlat due to strong chemical bonding. Reducing κlat of AMg2X2 is an important route for improving thermoelectric performance. Herein, it is found that Cd doping at the Mg site in CaMg2Bi2 can weaken intralayer covalent bonds and soften acoustic phonons, as well as fill the optical phonon gap. These effects result in large atomic displacement, low phonon group velocity, and strong lattice vibration anharmonicity. Doping 10% Cd leads to a reduction of 56% in the κlat of CaMg2Bi2. Moreover, Cd doping promotes orbital alignment and thus increases the density‐of‐states effective mass and Seebeck coefficient. Eventually, in conjunction with carrier concentration optimization by Na doping and band structure engineering by Ba doping, a high ZT of ≈1.3 at 873 K in (Ca0.85Ba0.15)0.995Na0.005Mg1.85Cd0.15Bi2 sample is realized. This work highlights the significant role of manipulating chemical bonding in suppressing phonon propagation of semiconductors. [ABSTRACT FROM AUTHOR]

A first-principles method was used to explore the influence of tensile strain on the electrical and optical characteristics of Nb-doped MoSe2. The tensile strain has been discovered to have a higher influence on the electrical structure of the Nb-doped MoSe2 system than pure monolayer MoSe2. According to the energy band structure study, the pure monolayer MoSe2 is a direct bandgap semiconductor, but the system doped with Nb instead of Mo atoms is a p-type-doped semiconductor. The bandgap of the Nb-doped MoSe2 system decreases gradually with the increase of tensile strain, but still maintains the p-type semiconductor properties, and the bandgap of the pure monolayer MoSe2 also decreases gradually with the increase of tensile strain. From the density of states analysis, it is found that for the total density of states of the doped system at different tensile strains, it is mainly contributed by the Mo-4d and Se-4p orbitals. The optical properties analysis showed that the doped system under tensile strain had higher absorption coefficient and reflectance peak than the Nb-doped MoSe2 system without tensile strain. Additionally, the doped system showed redshift phenomenon in both the absorption and reflection peaks as the tensile strain increased. [ABSTRACT FROM AUTHOR]

Improving ferro-piezoelectric properties of niobate-based perovskites is highly desirable for developing eco-friendly high-performance sensors and actuators. Although electro-strain coupling is usually obtained by constructing multiphase boundaries via complex chemical compositions, defect engineering can also create opportunities for novel property and functionality advancements. In this work, a representative tetragonal niobate-based perovskite, i.e., KNbO3, is studied by using first-principles calculations. Two intrinsic types of Nb antisite defect complexes are selected to mimic alkali-deficiency induced excess Nb antisites in experiments. The formation energy, electronic profiles, polarization, and piezoelectric constants are systematically analyzed. It is shown that the structural distortion and chemical heterogeneity around the energetically favorable antisite pair defects, i.e., ( Nb K 4 · + K Nb 4 ′ ), lower the crystal symmetry of KNbO3 from tetragonal to triclinic phase, and facilitate polarization emergence and reorientation to substantially enhance intrinsic ferro-piezoelectricity (i.e., spontaneous polarization Ps of 68.2 μC/cm2 and piezoelectric strain constant d33 of 228.3 pC/N) without complicated doping and alloying. [ABSTRACT FROM AUTHOR]

[Display omitted] In this study, the impact of lead (Pb) doping on the photoelectrochemical (PEC) water splitting performance of tungsten oxide (WO 3) photoanodes was investigated through a combination of experimental and theoretical approaches. Pb-doped WO 3 nanostructured thin films were synthesized hydrothermally, and extensive characterizations were conducted to study their morphologies, band edge, optical and photoelectrochemical properties. Pb-doped WO 3 exhibited efficient carrier density and charge separations by reducing the charge transfer resistance. The 0.96 at% Pb doping shows a record photocurrent of ∼ 1.49 mAcm−2 and ∼ 3.44 mAcm−2 (with the hole scavenger) at 1.23 V vs. RHE besides yielding a high charge separation and Faradaic efficiencies of ∼ 86 % and > 90 %, respectively. A shift in the Fermi level towards the conduction band was also observed upon the Pb doping. Additionally, density functional theory (DFT) simulations demonstrated the changes in the density of states and bandgap upon Pb doping, exhibiting favorable changes in the surface and bulk properties of WO 3. [ABSTRACT FROM AUTHOR]

Context: In this paper, the effects of torsional deformation on the electronic properties of intrinsic WSe2 system and Ca-adsorbed WSe2 system were systematically studied by first-principles method. The results show that Ca can be stably adsorbed on the vacancy (H site) of WSe2 surface in all deformation systems, and the adsorption energy of the system without deformation is the highest. Intrinsic WSe2 is a semiconductor with a direct band gap of 1.53 eV. The torsional deformation makes WSe2 change from a direct band gap semiconductor to an indirect band gap semiconductor and finally to a metal property. The adsorption of Ca makes the conduction band of WSe2 move down and increases the number of peaks in the conduction band region. The new density of state peaks are mainly derived from the contribution of W-d, Se-p, and d orbitals of adsorbed atoms in each adsorption system. Mulliken charge analysis shows that Ca transfers most of the valence electrons to the substrate, and the torsional deformation changes the amount of transferred charge. The twist deformation reduces the diffusion barrier of Ca on WSe2 surface from 0.20 to 0.14 eV. The above results provide a basis for the improved application of WSe2 in ion batteries. Methods: In this study, all the first-principles calculations are based on Materials Studio 8.0 software package. The generalized gradient approximation (GGA) functional Perdew-Burke-Ernzerhof (PBE) is used for the electron exchange correlation interactions in all systems. The optimization algorithm uses Broyden-Fletcher-Goldfarb-Shanno (BFGS) to optimize the model structure and calculate the energy. The measured cutoff energy is optimized to 450 eV, and the radius of the vacuum layer in the Z-axis direction is 20 Å. The K-point of 7 × 7 × 1 is selected by Monkhorst–Pack method. The structural optimization criterion is selected, the convergence radius of the force is 0.01 eV/Å, and the displacement radius between atoms is within 0.001 Å distance. The energy convergence radius of each atom is less than 1.0 × 10−6 eV/atom. [ABSTRACT FROM AUTHOR]

The titanium dioxide (TiO2) semiconductor's wide band gap property restricts its application in a variety of fields. To ensure cost-effectiveness and time efficiency, researchers emphasized material modeling and theoretical analysis. This study employs a Density Functional Theory approach to investigate how the presence of transition metal elements (TME) like rhodium (Rh) and rhenium (Re) affects the optoelectronic properties of TiO2. The study was carried out using the VASP software package and the plane-wave pseudopotential technique. The formation energy, electronic band structure, and optical properties of TiO2 were affected by the addition of both Rh and Re as doping materials. The outcomes of the band structure and total density of states (TDOS), point out notable alterations in the energy gap (Eg) of TiO2. The plot of the band structure illustrates that the introduction of Re leads to a more substantial reduction in the TiO2 band gap compared to Rh. The introduction of numerous sub-states into the band gap causes the valence band to approach the conduction band at the Gamma point. The band gap reduction caused by the addition of Rh and Re TME is confirmed by the relocation of the TDOS to lower energies in the doped TiO2 structure. Furthermore, significant changes in the partial density of states of TiO2 upon Re doping have been observed at the bottom of the conduction band, highlighting the effectiveness of Re doping in modifying the electronic band structure of TiO2. The outcomes of band structure and TDOS proved that TME with high atomic mass is certain to decrease TiO2's band gap to the range required for usage as a photocatalytic material. Rh and Re doping in TiO2 alter their optical properties, making them suitable for optoelectronic devices. [ABSTRACT FROM AUTHOR]

In the present study, we investigate the influence of boron (B) and phosphorus (P) (p- and n-type, respectively) doping on the electronic properties of ultra-thin silicon nanowires (SiNWs) by gradient-corrected density functional calculations with the Perdew–Burke–Ernzerhof (PBE) approximation. In the limit of very small diameters (5–8 Å), both pristine and highly active unsaturated SiNWs with orientations along the [001] and [111] directions exhibit electronic states around the Fermi level, indicative of conductive properties. Conduction is further enhanced by the introduction of doping atoms, as demonstrated by the relative change in the band structures of SiNWs with and without B and P doping. This investigation provides an important insight into the electronic states of SiNWs, which are candidates for future electronics or sensing applications. [ABSTRACT FROM AUTHOR]

Biphenylene network (BPN) structures have garnered attention owing to the presence of 4-, 6-, 8-, and 12-membered rings in their unit cells, leading to unique properties. Additionally, the versatility of aluminum (Al) combined with group V elements, particularly nitrogen (N) atoms, presents promising applications across various domains. These factors have motivated us to investigate BPN-AlN structures containing 4-, 6-, and 12-membered rings using density functional theory methods. These rings lead to large holes, making this structure useful for ion storage in energy storage materials. This study contains the stability (thermal, mechanical, and dynamical), structural, electronic, thermoelectric, and optical properties of the BPN-AlN nanosheet. The dynamic stability of the proposed BPN-AlN nanosheet was confirmed by the absence of negative modes in the phonon dispersion spectrum. Furthermore, minimal energy fluctuations in the ab initio molecular dynamics simulation, even at a high temperature of 1500 K, prove the thermal stability of the BPN-AlN nanosheet. This calculation leads to the BPN-AlN nanosheet's high melting temperature. The BPN-AlN nanosheet has exhibited semiconductor behavior with a high indirect band gap of 4.025 eV. By investigating the electron localization function, the BPN-AlN nanosheet shows polar ionic bonds, which introduces this nanosheet as a good candidate for absorbing numerous polar substances like sensors. The Seebeck coefficient exhibits the highest peak values of 359 μV/K (n-type) and 305 μV/K (p-type) at 300 K. Additionally, the ultralow lattice thermal conductivity, approximately 0.46 W/mK at 300 K, confirms the superior thermoelectric properties of BPN-AlN nanosheets. The study of the optical properties of the BPN-AlN nanosheet reveals significant absorption and minimal reflection of ultraviolet light, highlighting the potential of the BPN-AlN nanosheet for applications in ultraviolet protection. The specific electronic and optical properties imply that the BPB-AlN nanosheet may be used in the generation of nano-optoelectronic technology design. [ABSTRACT FROM AUTHOR]

AbstractIn the thesis, we investigate a two-dimensional period slab composite structure composed of steel/epoxy and adhered with a series of heat films. Various types of periodic thermal fields are introduced into the structure by loading diverse powers of heat on the heat films. Leveraging the thermal sensitivity of epoxy, these introduced thermal fields facilitate changes and tuning in the band structures of the composite slab. Therefore, a thermal–mechanical coupling model based on finite element method via commercial software is established to obtain the dispersion curves and transmission spectrums of the period structure. The numerical prediction of band gaps indicates that band structures of composite slabs can be effectively tuned by thermal fields. Furthermore, intelligent waveguides and wave separators are designed by thermal fields with line-type or L-type of thermal defects. The results also exhibit an interesting phenomenon that in-plane wave and out-of-plane wave can be decoupled when T-type of thermal defects with proper heat flux are employed. The results of this research may lay theoretical foundation and provide a novel routine for the designing of intelligent acoustic devices such as waveguides and wave separators. [ABSTRACT FROM AUTHOR]

Employing density functional theory within the Wien2k code, first‐principle calculations are conducted to explore the impact of applied pressure up to 80 GPa on the structural, mechanical, thermal, and electronic characteristics of BaPbO3. Demonstrating metallic behavior with ductile attributes, BaPbO3 exhibits a decreasing anisotropic nature under escalating pressure. Evaluation of cubic elastic constants, optimization curves, and enthalpy of formation indicates the compound's mechanical and thermodynamic stability under high pressure conditions. Calculated values of C11 and C44 reflect heightened resistance to unidirectional compression and increased stiffness under pressure. These mechanical properties position BaPbO3 as a promising candidate for diverse industrial applications across varying pressure ranges, including utilization in piezoelectric materials (0–20 GPa) and high‐pressure sensors. Additionally, charge density contours suggest a combination of ionic (Ba─Pb) and covalent bonding (Pb─O) within the compound's constituent atoms. The material can exhibit potential applications as a piezoelectric sensor at 0–20 GPa, high‐pressure actuators ≈20 GPa, and as a high melting temperature resistive substrate for laser welding and cutting materials. [ABSTRACT FROM AUTHOR]

We discover a unique structural-modified diamond that exhibits similar symmetry and band gap energy to that of the pure diamond. We study a complex carbon-vacancy-hydrogen in the diamond using the density-functional-theory method. The defective models are created by adding H-interstitial (Hi, where i = 1, 2, 3 and 4) in the 3D diamond C-monovacancy. The result shows that carbon-vacancy-hydrogen defects significantly decreased the symmetry from Td to C2V. Likewise, the volumetric size of the systems is widening up to 48.70 %, while the optimized band gap energies are narrowing. Additional states appeared in the C-monovacancy, H1-V, H2-V, and H3-V systems which further improved electron mobility. The Hi compensates the C-monovacancy which further serves as a deep donor. Interestingly, H4-V exhibits similar symmetry and band gap energy to that of the pure diamond, but its volumetric size is 48.70 % wider. [ABSTRACT FROM AUTHOR]

In this work, [KNbO3]0.98-[A(Ni1/2Sn1/2)O3]0.02(A = Ba, Sr, Ca) photocatalytic materials were prepared using a solid-state method. The results show that changing the A-site doping element while keeping the B-site doping element constant leads to systematic variations in the band structure of KNbO3-based materials. The analysis reveals that as the ionic radius of the A-site dopant decreases, the conduction band and valence band of the samples exhibit an overall negative shift along the energy axis. The more negative conduction band energy level is favorable for electron reduction and hydrogen gas production. The hydrogen evolution rates of [KNbO3]0.98-[A(Ni1/2Sn1/2)O3]0.02(A = Ba, Sr, Ca) under simulated sunlight are 165.798 µmol/(g·h) (A = Ca), 151.697 µmol/(g·h) (A = Sr) and 119.487 µmol/(g·h) (A = Ba), respectively. [ABSTRACT FROM AUTHOR]

The superconductivity of CaC6 as a function of pressure and Ca isotopic composition was revisited using DFT calculations on a 2c–double hexagonal superlattice. The introduction of superlattices was motivated by previous synchrotron absorption and Raman spectroscopy results on other superconductors that showed evidence of superlattice vibrations at low (THz) frequencies. For CaC6, superlattices have previously been invoked to explain the ARPES data. A superlattice along the hexagonal c-axis direction is also illustrative of atomic orbital symmetry and periodicity, including bonding and antibonding s-orbital character implied by cosine-modulated electronic bands. Inspection of the cosine band revealed that the cosine function has a small (meV) energy difference between the bonding and antibonding regions, relative to a midpoint non-bonding energy. Fermi surface nesting was apparent in an appropriately folded Fermi surface using a superlattice construct. Nesting relationships identified phonon vectors for the conservation of energy and for phase coherency between coupled electrons at opposite sides of the Fermi surface. A detailed analysis of this Fermi surface nesting provided accurate estimates of the superconducting gaps for CaC6 with the change in applied pressure. The recognition of superlattices within a rhombohedral or hexagonal representation provides consistent mechanistic insight on superconductivity and electron−phonon coupling in CaC6. [ABSTRACT FROM AUTHOR]

This paper is a theoretical study of the piezoresistivity of germanene nanoribbons (GeNRs) of various structural modifications (arm-chair and zig-zag) with acceptor structural defects. Gallium atoms were chosen as impurities. A phenomenological expression for the band structure of nanoribbons (NRs) deformed by tension and compression is proposed. The dependencies of the longitudinal component of the elastic conductivity tensor on the relative deformation of tension and compression, the concentration of impurities, and the width of the NR are analyzed. [ABSTRACT FROM AUTHOR]

Covalent organic framework (COF) materials have aroused tremendous interest in photocatalytic applications due to their tunable pore structure and photoelectric properties. The regular nanopore of COF itself presents a strongly confinement effect, which provides a unique regulatory effect for photons, electrons, protons, and other quantum‐scale reaction groups. However, due to the weak surface electron coupling and transfer ability between the reactive groups and basic elements of its structural units, the activity of pure COFs photocatalyst is still not satisfactory. Therefore, the confinement modification strategy of confining low‐dimension entities within COFs has been proposed, thus realizing new active sites construction and band structure regulation has been intensively studied, but yet to be summarized systematically. In this paper, the semi‐conductivity of COFs is discussed dialectically based on photocatalytic thermodynamics, and the influence of internal linkage motifs and stacking behaviors on the band structure is collected. Then, the basic understanding of confinement characteristics and their influence on photocatalytic performance in dynamics is further explained according to the spatial dimension classification of low‐dimension entities. And the application and mechanism of these COF‐based confined catalysts in energy conversion reactions are discussed in detail. Lastly, the current challenges and development prospects of COF‐based confined hetero‐photocatalysts are discussed. [ABSTRACT FROM AUTHOR]

We concentrate on the skin effects and topological properties in the multilayer non-Hermitian Su–Schrieffer–Heeger (SSH) structure, by taking into account the nonreciprocal couplings between the different sublattices in the unit cells. Following the detailed demonstration of the theoretical method, we find that in this system, the skin effects and topological phase transitions induced by nonreciprocal couplings display the apparent parity effect, following the increase of the layer number of this SSH structure. On the one hand, the skin effect is determined by the parity of the layer number of this SSH system, as well as the parity of the band index of the bulk states. On the other hand, for the topological edge modes, such an interesting parity effect can also be observed clearly. Next, when the parameter disorders are taken into account, the zero-energy edge modes in the odd-layer structures tend to be more robust, whereas the other edge modes are easy to be destroyed. In view of these results, it can be ascertained that the findings in this work promote to understand the influences of nonreciprocal couplings on the skin effects and topological properties in the multilayer SSH lattices. [ABSTRACT FROM AUTHOR]

Aiming to address the vibration noise problems on ships, we constructed a piezoelectric phononic crystal (PC) plate structure model, solved the governing equations of the structure using the partial differential equations module (PDE) in the finite element softwareCOMSOL6.1, and obtained the corresponding energy band structure, transmission curves, and vibration modal diagrams. The application of this method to probe the structural properties of two-dimensional piezoelectric PCs is described in detail. The calculation results obtained using this method were compared with the structures obtained using the traditional plane wave expansion method (PWE) and the finite element method (FE). The results were found to be in perfect agreement, which verified the feasibility of this method. To safely and effectively adjust the bandgap within a reasonable voltage range, this paper explored the order of magnitude of the plate thickness, the influence of the voltage on the bandgap, and the dependence between them. It was found that the smaller the order of magnitude of the plate thickness, the smaller the order of magnitude of the band in which the bandgap was located. The magnitude of the driving voltage that made the bandgap change became smaller accordingly. The new idea of attaching the PC plate to the conventional plate structure to achieve a vibration damping effect is also briefly introduced. Finally, the effects of lattice constant, plate width, and thickness on the bandgap were investigated. [ABSTRACT FROM AUTHOR]

In cation–anion co-doping, rare earth elements excel at regulating the electronic structure of perovskites, leading to their improved photocatalytic performance. In this regard, the impact of co-doping rare earth elements at the Ba and Ti sites in BaTiO3 on its electronic and photocatalytic properties was thoroughly investigated based on 2 × 2 × 2 supercell structures of BaTiO3 with different La concentrations of 12.5% and 25% using DFT calculations. The band structure, density of states, charge density difference, optical properties, and the redox band edge of the co-doped models mentioned above were analyzed. The results indicated that the BaTiO3 structure co-doped with 25% La at the Ti site exhibited higher absorption in the visible range and displayed a remarkable photocatalytic water-splitting performance. The introduced La dopant at the Ti site effectively reduced the energy required for electronic transitions by introducing intermediate energy levels within the bandgap. Our calculations and findings of this study provide theoretical support and reliable predictions for the exploration of BaTiO3 perovskites with superior photocatalytic performances. [ABSTRACT FROM AUTHOR]

The electronic and optical properties of hydrogenated silicene at different torsion angles are investigated using the density functional theory (DFT). It was found that when silicene was hydrogenated, the Si atoms were pulled out of plane due to covalent interactions between the Si and H atoms, increasing their flexural height to 0.731 Å. Torsional deformation decreases the structural stability of hydrogenated silicene and its adsorption energy decreases with increasing twist angle. Under the effect of torsion deformation, the bandgap of hydrogenated silicene increases and then decreases. The bandgap is 2.168 eV at a torsion angle of 0∘, indicating a wide bandgap semiconductor. Mulliken's charge population analysis shows that charge transfer occurs between Si–H atoms, with Si atoms losing electrons and becoming positively charged and H atoms gaining electrons and becoming negatively charged. From the analysis of optical properties, the torsional deformation induced the maximum absorption and reflection peaks of all the hydrogenated silicene systems to appear in the ultraviolet region. Compared with the system without torsional deformation, these peaks exhibit varying degrees of red and blue shifts. The above findings provide guidance for the application of silicene in nanooptoelectronic devices. [ABSTRACT FROM AUTHOR]

ZnO is one of the most promising mid-high temperature thermoelectric materials because of low cost, easy preparation and favorable chemical stability. Herein, the influence mechanism of Alkaline earth metal Ba doping on the thermoelectric properties of ZnO was studied. It is found that Ba doping can effectively improve the carrier mobility and electrical conductivity for that Ba doping can shorten the Zn–O bond and enhance the overlap and hybridization of electron orbitals. The electronic density of states of Zn and O is significantly enhanced. The highest power factor of ∼7.95 μWcm−1K−2 was obtained at 873 K, which is ∼1.4 times higher than that of the undoped sample. Due to the decrease of Young's modulus caused by Ba doping and the enhancement of phonon scattering of heavy element, the thermal conductivity decreases obviously in the whole temperature range. Ba doping enhanced the effect of phonon glass-electron crystal, and the ZT value of ∼0.345 was obtained at 873 K, which is ∼3.52 times as that of the pristine ZnO. The results indicated that alkaline earth metal doping is an effective way to improve the thermoelectric properties of ZnO functional materials. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have shown high optical absorption and consequently provide high conversion efficiency with stable performance. In our work, CH3NH3PbI3 (MAPbI3) as an absorber layer is analyzed for different crystalline structures. Cubic, tetragonal, and orthorhombic phases of perovskite material are investigated to check the impact of the crystalline structure on the solar cell performance. Both density of states and band structure are studied using Quantum-ESPRESSO package depending on density functional theory. Then, all relevant parameters were employed in SCAPS software and comprehensive study was done for examining the effect of the crystalline structure of perovskite layer on the solar cell performance. In-depth, analyses were conducted to evaluate key parameters, including open circuit voltage (Voc), short circuit current (Isc), fill factor (FF), and power conversion efficiency (PCE) considering the variations of perovskite layer thickness and bulk defect densities. The obtained results indicate that cells with cubic MAPbI3, which shows a notably higher bandgap of 1.7 eV and an enhanced optical absorption coefficient, especially in the higher wavelength range (around 105 cm−1), show better performance for almost all three scenarios. Cubic MAPbI3 cells achieve relatively higher peak efficiency of 26% when the absorber layer thickness is almost 900 nm. The investigation into absorber bulk defect densities reveals the critical role of defect levels in PSC performance. Adjusting defect levels from 1014 cm−3 to 1018 cm−3 results in deteriorating trends in Voc, Jsc, FF, and PCE. Jsc remains stable until a defect level of 1017 cm−3, highlighting a threshold where defects begin to impact charge carrier generation and separation. Doping effect has been studied, PCE remains stable until a critical doping level of 1016 cm−3 after which it drops significantly which indicates that doping is cautioned against due to its adverse effects on material and carrier transport. This finding holds significant promise for experimental solar cell fabrication, as it suggests that cubic MAPbI3's superior bandgap and enhanced optical absorption could lead to more efficient and robust photovoltaic devices in real-world applications. [ABSTRACT FROM AUTHOR]

Perovskite solar cells (PSCs) have shown high optical absorption and consequently provide high conversion efficiency with stable performance. In our work, CH3NH3PbI3 (MAPbI3) as an absorber layer is analyzed for different crystalline structures. Cubic, tetragonal, and orthorhombic phases of perovskite material are investigated to check the impact of the crystalline structure on the solar cell performance. Both density of states and band structure are studied using Quantum-ESPRESSO package depending on density functional theory. Then, all relevant parameters were employed in SCAPS software and comprehensive study was done for examining the effect of the crystalline structure of perovskite layer on the solar cell performance. In-depth, analyses were conducted to evaluate key parameters, including open circuit voltage (Voc), short circuit current (Isc), fill factor (FF), and power conversion efficiency (PCE) considering the variations of perovskite layer thickness and bulk defect densities. The obtained results indicate that cells with cubic MAPbI3, which shows a notably higher bandgap of 1.7 eV and an enhanced optical absorption coefficient, especially in the higher wavelength range (around 105 cm−1), show better performance for almost all three scenarios. Cubic MAPbI3 cells achieve relatively higher peak efficiency of 26% when the absorber layer thickness is almost 900 nm. The investigation into absorber bulk defect densities reveals the critical role of defect levels in PSC performance. Adjusting defect levels from 1014 cm−3 to 1018 cm−3 results in deteriorating trends in Voc, Jsc, FF, and PCE. Jsc remains stable until a defect level of 1017 cm−3, highlighting a threshold where defects begin to impact charge carrier generation and separation. Doping effect has been studied, PCE remains stable until a critical doping level of 1016 cm−3 after which it drops significantly which indicates that doping is cautioned against due to its adverse effects on material and carrier transport. This finding holds significant promise for experimental solar cell fabrication, as it suggests that cubic MAPbI3's superior bandgap and enhanced optical absorption could lead to more efficient and robust photovoltaic devices in real-world applications. [ABSTRACT FROM AUTHOR]