Lattice Parameters Research Articles

Flux Synthesis of Alkaline-Earth Lanthanide Borates as Potential Nuclear Waste Forms.

Neodymium is typically considered the best surrogate for trivalent americium and can be used to identify Am3+ containing materials that are likely to form. We have explored the alkaline-earth lanthanide borate phase space using alkaline-earth halide/carbonate fluxes. This resulted in the synthesis of new compounds AE5Ln(BO3)4X (AE = Ca, Sr; Ln = Pr, Nd, Eu, Tb; X = Cl, Br) and AE3Ln2(BO3)4 (AE = Sr, Ba; Ln = Pr, Nd) as well as the synthesis of two compounds of Ba8Ln2(BO3)6(B2O5) (Ln = Eu, Tb) crystallizing in a new structure type. Ba8Ln2(BO3)6(B2O5) crystallizes in the space group P21/n with lattice parameters a = 8.6002(3) Å, b = 7.9245(3) Å, c = 17.6697(7) Å, and β = 91.3560(10)° for the Eu analogue, and the structure contains isolated LnO8 polyhedra connected into a framework by BO3 and B2O5 units. The fluorescence emission spectra of AE5Ln(BO3)4X (AE = Ca, Sr; Ln = Eu, Tb; X = Cl, Br) and Ba8Ln2(BO3)6(B2O5) (Ln = Eu, Tb) are reported.

First-principles study of non-linear thermal expansion in cadmium titanate by molecular dynamics incorporating nuclear quantum effects

First-principles molecular dynamics (FPMD) simulations were applied for analyzing structural evolutions around the paraelectric-ferroelectric phase transition temperature in the perovskite-type cadmium titanate, CdTiO3. Since the phase transition is reported to occur at the low temperature around 80 K, the quantum thermal bath (QTB) method was utilized in this study, which incorporates the nuclear quantum effects (NQEs). The structural evolutions in the QTB-FPMD simulations are in reasonable agreement with the experimental results, by contrast in the conventional FPMD simulations using the classical thermal bath (CTB-FPMD). Especially, the non-linear thermal expansion of lattice constants around the phase transition temperature was well reproduced in the QTB-FPMD with the NQEs. Thus, the NQEs are of importance in phase transitions at low temperatures, particularly below the room temperature, and the QTB is useful in that it incorporates the NQEs in MD simulations with low computational costs comparable to the conventional CTB.

Water Effect on the Electronic Properties and Lithium-Ion Conduction in a Defect-Engineered LiFePO4 Electrode

Defect-engineering accelerates the conduction of lithium ions in the cathode materials of lithium-ion batteries. However, the effects of defect-engineering on ion conduction and its mechanisms in humid environments remain unclear in the academic discourse. Here, we report on the effect of vacancy defects on the electronic properties of and Li-ion diffusion in a LiFePO4 material in humid environments. The research findings indicate that vacancy defects reduce the lattice constant and unit cell volume of LiFePO4. Additionally, the water molecules occupy the Li-ion vacancies, leading to an increase in the lattice constant of LiFePO4. The computational results of the electronic properties show that the introduction of water molecules induces a transition in LiFePO4 from a semiconductor to a metallic behavior, with a transfer of 0.38 e of charge from the water molecules to LiFePO4. Additionally, the migration barrier for Li ions in the H2O + LiFePO4 system is found to be 0.50 eV, representing an 11.1% increase compared to the pristine LiFePO4 migration barrier. Our findings suggest that water molecules impede the migration of Li ions and provide important insights into the effect of defect-engineering on electronic properties and ion conduction under humid conditions.

Systematic improvement of x -dependent unpolarized nucleon generalized parton distributions in lattice-QCD calculation

We present a first study of the effects of renormalization-group resummation (RGR) and leading-renormalon resummation (LRR) on the systematic errors of the unpolarized isovector nucleon generalized parton distribution in the framework of large-momentum effective theory. This work is done using lattice gauge ensembles generated by the MILC Collaboration, consisting of 2+1+1 flavors of highly improved staggered quarks with a physical pion mass at lattice spacing a≈0.09 fm and a box width L≈5.76 fm. We present results for the nucleon H and E generalized parton distributions (GPDs) with average boost momentum Pz≈2 GeV at momentum transfers Q2=[0,0.97] GeV2 at skewness ξ=0 as well as Q2∈0.23 GeV2 at ξ=0.1, renormalized in the modified minimal subtraction (MS¯) scheme at scale μ=2.0 GeV, with two- and one-loop matching, respectively. We demonstrate that the simultaneous application of RGR and LRR significantly reduces the systematic errors in renormalized matrix elements and distributions for both the zero and nonzero skewness GPDs, and that it is necessary to include both RGR and LRR at higher orders in the matching and renormalization processes. Published by the American Physical Society 2024

Charge density wave transition and unusual resistance hysteresis in vanadium disulfide (1T-VS2) microflakes

Abstract We report existence of charge density wave (CDW) transition with unusual resistivity hysteresis in stable micro-flakes of 2D transition metal di-chalcogenide (TMDC) vanadium disulfide (1T-VS2) as ascertained by structural studies, Raman spectroscopy, heat capacity, resistivity measurements and supported by phonon calculations based on density functional theory. The CDW transition occurs at around 296 K on cooling and manifests itself by the onset of resistivity with a negative temperature coefficient, which we identify as the transition temperature (TCDW). The transition is identified by a distinct peak in the heat capacity at T ≈ TCDW along with anomalies in temperature variation of the lattice parameters and complimentary signatures in electron diffraction and temperature-dependent Raman spectroscopy. The temperature-dependent resistivity measurements done with different ramp rates of cooling and heating show strong hysteresis and a low temperature relaxation pointing to the existence of metastable states below the transition. The Raman spectroscopy data show a hysteresis loop below the onset of the CDW transition. The phonon band structure calculations carried out on the 1T-VS2 system show the existence of the phonon mode softening along the diagonal of the Brillouin zone, which is pronounced near the transition temperature implying the prominent role of the mode softening as a driver of the transition. The results imply that the formation of CDW is sensitive to phonon mode softening rather than energy gap opening at the Fermi level.

Fiber optic probe integrated with colloidal nanoparticles with directional diffraction selectivity for magnetic field vector detection

A fiber optic probe integrated with colloidal nanoparticles with directional diffraction selectivity is proposed for wide-bandwidth magnetic field vector detection. The probe is constructed with the multimode fiber in which the end-surface is integrated with the Fe3O4@C colloidal nanoparticles by a silicone tube. The colloidal nanoparticles form a three-dimensional photonic crystal structure by magnetic field for diffraction selectivity. The lattice constant and diffraction angle are adjusted by the intensity and direction of the magnetic field, respectively. Obtaining the directional diffraction light through the magnetic field-induced photonic band gap shift with the wavelength blue shift and reflectivity change is confirmed by theory and experiment. The results show that the maximum sensitivity reaches up to 19.7 nm/mT in response range from 13 mT to 200 mT. For vector detection, the peak wavelength shift from 740 nm to 485 nm and reflectance shift from 71% to 7% covering the 0–45° region is verified. In addition, the proposed method could decouple intensity and direction of the magnetic field completely. The fiber optic probe integrated with colloidal nanoparticles has wide detection range and high sensitivity with rapid response. It will open up new horizons for inspiring design and application of magnetic field vector detection in robot posture control and motion perception.

The thermal expansion of Ti-substituted CaAl12O19

CaAl12O19, which can incorporate Ti as both Ti3+ and Ti4+ (charge coupled substitution with Mg2+), is one of the first minerals to condense from a gas of solar composition and is used as a ceramic. It is variously known as hibonite, calcium hexaluminate (CaO.6Al2O3), and CA6. The lattice parameters and unit cell volumes of Ti-substituted hibonite (P63/mmc) with the formulae CaAl11.8Ti3+0.2O19 and CaAl9.8Ti3+0.54Mg0.83Ti4+0.83O19 were determined as a function of temperature from ~ 10 to 275 K by neutron powder diffraction. The thermal expansion is highly anisotropic with the expansion in c a factor of ~ 5 greater than that in a. The change in a is approximately equal for the two compounds whereas the change in c is almost 50% larger for CaAl11.8Ti3+0.2O19. CaAl11.8Ti3+0.2O19 also exhibits negative thermal expansion between 10 and 70 K. The change in unit cell volume with temperature of both compositions is well described by a two term Einstein expression. The large change in c is consistent with substitution of Ti onto the M2 and M4 sites of the R-block structural unit.

Structural changes in Ge1−xSnx and Si1−x−yGeySnx thin films on SOI substrates treated by pulse laser annealing

Ge1−xSnx and Si1−x−yGeySnx alloys are promising materials for future opto- and nanoelectronics applications. These alloys enable effective bandgap engineering, broad adjustability of their lattice parameter, exhibit much higher carrier mobility than pure Si, and are compatible with the complementary metal-oxide-semiconductor technology. Unfortunately, the equilibrium solid solubility of Sn in Si1−xGex is less than 1% and the pseudomorphic growth of Si1−x−yGeySnx on Ge or Si can cause in-plane compressive strain in the grown layer, degrading the superior properties of these alloys. Therefore, post-growth strain engineering by ultrafast non-equilibrium thermal treatments like pulse laser annealing (PLA) is needed to improve the layer quality. In this article, Ge0.94Sn0.06 and Si0.14Ge0.8Sn0.06 thin films grown on silicon-on-insulator substrates by molecular beam epitaxy were post-growth thermally treated by PLA. The material is analyzed before and after the thermal treatments by transmission electron microscopy, x-ray diffraction (XRD), Rutherford backscattering spectrometry, secondary ion mass spectrometry, and Hall-effect measurements. It is shown that after annealing, the material is single-crystalline with improved crystallinity than the as-grown layer. This is reflected in a significantly increased XRD reflection intensity, well-ordered atomic pillars, and increased active carrier concentrations up to 4 × 1019 cm−3.

Suppression of Lattice Doubling in Quasi-Skutterudite La3Rh4Sn13: A Comparison of Temperature and Hydrostatic Pressure Routes.

We present structural properties at different temperatures and high-pressure (HP) of La3Rh4Sn13 which is one of the interesting systems in the Remika phase RE3Rh4Sn13 (RE=Sr, Ca, La, Pr, Ce) quasi-skutterudite series using synchrotron diffraction. Data at ambient conditions revealed the presence of several weak reflections, which could be accounted only with a superlattice I* structure (I4132) with lattice parameter a~19.457 Å. However, above 350 K, a complete suppression of the weak superlattice reflections of the I* structure is observed. Data at higher temperatures is found to be well described by the I structure (Pm-3n) having half the lattice parameter compared to the I* structure. HP-XRPD at ambient temperature showed that pressures greater than 7.5 GPa result in similar suppression of the weak I* superlattice reflections. Data at higher pressures is found to be well described by the I structure (Pm-3n), similar to the high-temperature phase. HP Raman measurements demonstrated changes that seem to be consistent with a locally more ordered structure as in the case of the I*→I transition. Our findings on La3Rh4Sn13 open up new avenues to study unexplored HP phenomena, especially the superconductivity in these Remika phase quasi-skutterudites.

Superconductivity investigation of (Bi,Pb)-2223 added with different nanoferrites and their composites

Abstract In this study, the impact of different types of nanoferrites additions of Zn0.5Ni0.5Fe2O4 and Ba0.4Sr0.4Ca0.2Fe12O19 nanoparticles and their nanocomposite of (Zn0.5Ni0.5Fe2O4)0.5 (Ba0.4Sr0.4Ca0.2Fe12O19)0.5 on the structural and normal state resistivity of Bi1.6Pb0.4Sr2Ca2Cu3O10, ((Bi,Pb)-2223) superconducting phase were systematically investigated. The samples were synthesised using high purity oxide powders via a solid-state reaction approach. Based on the Rietveld analysis of X-ray diffraction (XRD) data, the tetragonal structure of (Bi,Pb)-2223 was established to be the predominant phase for all composite samples of the three nano-additions' contents. However, a little change to the lattice parameters (a and c) was obtained. Furthermore, the small amounts (0.04 wt. %) of Ba0.4Sr0.4Ca0.2Fe12O19 and (Zn0.5Ni0.5Fe2O4)0.5(Ba0.4Sr0.4Ca0.2Fe12O19)0.5 improved the development of the (Bi,Pb)-2223 phase. The volume fraction of the (Bi,Pb)-2223 phase increased from 86.47 % to 88.73 % and 88.69 %, respectively. Then, it declined to 74.25 % and 71.48 % upon rising x to 0.40 wt. %, respectively, as well as for Zn0.5Ni0.5Fe2O4 nanoparticles up to 0.40 wt.%. SEM images verify the host superconducting matrix's granular structure for all three nanoadditions up to 0.40 wt.%. The existence of three nano additions in the host superconductor matrix is verified by employing energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) analysis. The measurements for the resistivity dependency of temperature presented that, as compared to the pure sample (Tc = 108.67 K), the nano-(Zn0.5Ni0.5Fe2O4)xadded in the (Bi,Pb)-2223 phase exhibits more negative impact than it is with the other two additions.In contrast, the nano-(Ba0.4Sr0.4Ca0.2Fe12O19)x has the highest value of TC with a value of 110.95 K at x = 0.04 wt.%. Furthermore, the superconducting transition width (∆Tc) improved for all composite samples except for the sample at x = 0.04 wt.%, for Ba0.4Sr0.4Ca0.2Fe12O19 and (Zn0.5Ni0.5Fe2O4)0.5 (Ba0.4Sr0.4 Ca0.2Fe12O19)0.5 which showed the sharpest transition width. This suggests that their addition is anticipated to act as artificial pinning centers and strengthen the coupling between the grains in the (Bi,Pb)-2223 ceramic.

Synthesis and Characterisation of Nanocrystalline CoxFe1−xGDC Powders as a Functional Anode Material for the Solid Oxide Fuel Cell

The necessity for high operational temperatures presents a considerable obstacle to the commercial viability of solid oxide fuel cells (SOFCs). The introduction of active co-dopant ions to polycrystalline solid structures can directly impact the physiochemical and electrical properties of the resulting composites including crystallite size, lattice parameters, ionic and electronic conductivity, sinterability, and mechanical strength. This study proposes cobalt–iron-substituted gadolinium-doped ceria (CoxFe1-xGDC) as an innovative, nickel-free anode composite for developing ceramic fuel cells. A new co-precipitation technique using ammonium tartrate as the precipitant in a multi-cationic solution with Co2+, Gd3+, Fe3+, and Ce3+ ions was utilized. The physicochemical and morphological characteristics of the synthesized samples were systematically analysed using a comprehensive set of techniques, including DSC/TGA for a thermal analysis, XRD for a crystallographic analysis, SEM/EDX for a morphological and elemental analysis, FT-IR for a chemical bonding analysis, and Raman spectroscopy for a vibrational analysis. The morphological analysis, SEM, showed the formation of nanoparticles (≤15 nm), which corresponded well with the crystal size determined by the XRD analysis, which was within the range of ≤10 nm. The fabrication of single SOFC bilayers occurred within an electrolyte-supported structure, with the use of the GDC as the electrolyte layer and the CoO–Fe2O3/GDC composite as the anode. SEM imaging and the EIS analysis were utilized to examine the fabricated symmetrical cells.

The effect of vanadium on the magnetic and mechanical properties of B2 FeCo alloy: a DFT approach

FeCo alloys play an important role in soft magnetic materials with a wide range of technological applications due to their high saturation magnetization and Curie temperature. However, these alloys have low ductility at room temperature. The ductility can be improved by the ternary addition of elements such as V. A density functional theory supercell approach was used to generate B2 Fe50Co50-xVx (0 < x < 50) structures and the properties were evaluated at different atomic percentage compositions to determine the ductility at room temperature. The structures were fully optimized to obtain better equilibrium ground-state properties such as lattice parameters and thermodynamic properties for both binary and ternary systems. The stability of Fe50Co50-xVx was evaluated from the heats of formation, elastic properties, and phonon dispersion curves. Furthermore, magnetic strength was evaluated from magnetic moments. It was found that all structures are thermodynamically stable due to the negative heats of formation. The calculated Pugh's ratio and Poisson's ratio confirm that alloying with V effectively improved the ductility. It was also found that Fe50Co50-xVx showed a positive shear modulus for the entire concentration range investigated, in agreement with phonon dispersion curves. The ternary addition of V to the FeCo system resulted in reduced magnetic strength due to a decrease in magnetic moments. These findings reveal that B2 FeCo-V alloys can be used as components and actuators for the automotive industry.

A comparative study of structural, elastic, electronic, thermophysical, and optical properties of cubic binary lave-phase intermetallic compounds of HfX2 (X = cr, mo, and W): An ab initio insight

In the present work, we have made a comparative investigation on the structural, elastic, electronic, thermos-physical, and optical properties of cubic binary lave phase intermetallic compound with the common formula HfX2 (X = Cr, Mo and W) based on Density Functional Theory (DFT) using CASTEP. The result of geometrical optimization has been strongly agreed with the experimental results. The HfW2 compound exhibits larger lattice parameters and volumes than HfMo2 and HfCr2 because of the variation of atomic radii of the exhibiting elements in the studied compounds. The elastic properties show that each of the compounds in the ground state is mechanically stable and has a highly ductile nature. Band structures and energy densities of states have been studied to learn more about electronic properties. These compounds display metallic properties in their electrical band structures. They also have high machinability, a low Debye temperature, low bond hardness, and a remarkably high melting point. Our investigation thoroughly examined the reflectivity, absorption coefficient, refractive index, dielectric function, optical conductivity, and loss function of these metals. The optical absorption, reflectivity spectra, and refractive index of HfX2 (X = Cr, Mo, and W) indicate their potential for use as solar reflectors in the IR-Vis region and UV–Vis absorbers.

Effects of Ti substitution by Zr, on the microstructure and hydrogen storage properties OF Ti2-xZrxCrV (x = 0.5, 1, 1.5, 2) alloys

The effect of the substitution of Ti by Zr on the crystal structure, microstructure, and first hydrogenation behavior of Ti2-xZrxCrV where X = 0.5, 1.0, 1.5, and 2.0 have been investigated. The samples were synthesized by arc-melting and characterized by X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The hydrogenation capacity was measured using a home-made Sieverts apparatus. Pure-Ti2CrV crystallizes in a body-centered cubic structure (BCC). Substitution of Ti by Zr leads to the appearance of a secondary phase, namely a C15 Laves phase for the Ti-containing samples, and C15 Laves phase plus a Zr-rich phase for the X = 2.0 sample. The substitution of Ti by Zr increased the lattice parameters in both phases for all samples. Increasing Zr content made the first hydrogenation faster but reduced the hydrogen capacity.

Light-trapping by wave interference in intermediate-thickness silicon solar cells

The power conversion efficiency of crystalline silicon (c − Si) solar cells have witnessed a 2.1% increase over the last 25 years due to improved carrier transport. Recently, the conversion efficiency of c − Si cell has reached 27.1% but falls well below the Shockley-Queisser limit as well as the statistical ray-optics based 29.43% limit. Further improvement of conversion efficiency requires reconsideration of traditional ray-trapping strategies for sunlight absorption. Wave-interference based light-trapping in photonic crystals (PhC) provides the opportunity to break the ray-optics based 4n 2 limit and offers the possibility of conversion efficiencies beyond 29.43% in c − Si cells. Using finite difference time domain simulations of Maxwell’s equations, we demonstrate photo-current densities above the 4n 2 limit in 50 − 300µm-thick inverted pyramid silicon PhCs, with lattice constant 3.1µm. Our 150µm-thick PhC design yields a maximum achievable photo-current density (MAPD) of 45.22mA/cm 2. We consider anti-reflection coatings and surface passivation consisting of SiO 2 − SiN x − Al 2 O 3 stacks. Our design optimization shows that a 80 − 120 − 150nm stack leads to slightly better solar light trapping in photonic crystal cells with thicknesses <50µm, whereas the 80 − 40 − 20nm stack performs better for cells with thicknesses >100µm. We show that replacing SiN x with SiC may improve the MAPD for PhC cells thinner than 100µm. For a fixed lattice constant of 3.1µm, we find no significant improvement in the solar absorption for 50 and 100µm-thick cells relative to a 15µm cell. A substantial improvement in the MAPD is observed for the 150µm cell, but there is practically no improvement in the solar light absorption beyond 150µm thickness.

Van der Waals mid-wavelength infrared detector linear array for room temperature passive imaging.

Passive imaging for mid-wave infrared (MWIR) is resistant to atmospheric pollutants, guaranteeing image clarity and accuracy. Arrayed photodetectors can simultaneously perform radiation sensing to improve efficiency. Room temperature van der Waals (vdWs) photodetectors without lattice matching have evolved rapidly with optimized stacking methods, primarily for single-pixel devices. The urgent need to implement arrayed devices aligns with practical demands. Here, we present an 8 by 1 black phosphorus/molybdenum sulfide (BP/MoS2) vdWs photodetector linear array with a fill-factor of ~77%, fabricated using a temperature-assisted sloping transfer method. The flat interface and uniform thickness facilitate carrier transport and minimize pixel nonuniformities, showing an average peak detectivity (D*) of 2.34 × 109 cm·Hz1/2·W-1 in the mid-wave infrared region. Compared to a single pixel, push-broom scanning passive imaging is eight times more efficient and further enhanced through mean filtering and fast Fourier transform filtering for strip noise correction. Our study offers guidance on vdWs arrayed devices for engineering applications.

Wafer-scale mesoporous GaN distributed bragg reflectors with enhanced luminescence for Eu doped β-Ga2O3 thin films

Wafer-scale Mesoporous GaN (MP-GaN) distributed Bragg reflectors (DBRs) with high reflectivity (>99 %) are prepared by electrochemical etching, and then are used as the substrate in growth of large-area europium (Eu) doped Ga2O3 thin films via the pulsed laser deposition (PLD) technology. X-ray diffraction analysis shows that all Ga2O3 thin films with different doping concentration have monoclinic β-Ga2O3 structures with [−201] orientation. The angle of β-Ga2O3 (−201) peak decreases as Eu contents increases, which is due to the fact that Eu3+ substituting for Ga3+ rises the lattice constant of β-Ga2O3. With the increase of Eu doping, the photoluminescence (PL) of the Ga2O3 thin film is enhanced. The epitaxial relationship is β-Ga2O3 (−201) || GaN (0001) with β-Ga2O3 [010] || GaN [-12-10]. Compared to the sample without DBRs, wafer-scale Ga2O3 thin films with MP-GaN DBRs exhibit a markedly increased PL intensity, which is attributed to improved internal quantum efficiency (IQE) of Ga2O3 thin films and enhanced light extraction efficiency (LEE) related to the light reflection effect of MP-GaN DBRs.

Synthesis and characterization of cubic δ–phase stabilized Bi2O3 electrolytes by triple rare earth cation doping for intermediate temperatures SOFCs

Face–centered cubic–Bi2O3 (δ–phase), a high–ion conductor, is an essential solid electrolyte option, particularly for low–low–temperature SOFC applications. It is widely accepted that δ–Bi2O3 exhibits higher conductivity than the YSZ electrolytes typically utilized in HT–SOFC units. The present study investigates the structural, thermal, surface, and conductivity characteristics of the Bi2O3 electrolytes co–doped with Tb–Sm–Gd rare earth. The XRD data indicate that, except composition 20Tb20Sm20Gd, all compositions are stabilized with the cubic δ–phase at room temperature. The estimated lattice constants additionally suggest lattice contraction, confirming that the partial cation substitutes between host Bi3+ and rare earth cations are successful. The DTA curves do not have any endothermic or exothermic peaks, indicating a possible phase transition. Arrhenius plots prove that DC conductivity decreases as the dopant ratio increases, implying a drop in polarization power. The highest conductivity is found to be 0.131 S/cm for the composition 10Tb10Sm10Gd.

Flux Crystal Growth, Structure, and Optical Properties of LiLa3Ti2S3O6: An Oxysulfide Phase Derived from K2NiF4-Type Structure.

Single crystals of a new titanium oxysulfide, LiLa3Ti2S3O6, were grown from a KI molten salt. Single-crystal X-ray diffraction analysis revealed that LiLa3Ti2S3O6 crystallizes in the space group Pnma with lattice parameters of a = 11.7319(4) Å, b = 3.94787(14) Å, and c = 20.6885(6) Å. In this structure, the one-dimensional chains of corner-sharing TiO5S octahedra are further corner-linked via equatorial and apical oxygen atoms to form unique corrugated two-dimensional perovskite-type layers in the ab plane with one octahedral thickness. These layers were intervened along the c-axis by the LaS rock-salt layers corrugated concomitantly with the perovskite-type layers, and LiO2S2 tetrahedral chains were located between these two types of two-dimensional layers. LiLa3Ti2S3O6 can be viewed as a modified K2NiF4-type structure with TiO5S octahedral layers stacked in a zigzag manner along the c axis. The oxysulfide has a direct-type band gap of 1.85 eV, based on UV-vis-NIR diffuse reflectance measurements. First-principles calculations showed that the conduction band minimum mainly consists of Ti 3d orbitals, and the valence band maximum consists of S 3p, O 2p, and Li 2s orbitals. The electronic structures near the Fermi level are similar to those of the structurally related photocatalytic oxysulfides Y2Ti2S2O5 and La5Ti2CuS5O7.

Tailoring the geometry of visible and near-infrared light active CuSe nanostructure for enhanced photocatalytic activity

Semiconductor photocatalysts play a pivotal role in fostering a sustainable environment by harnessing solar energy directly into chemical energy to achieve various photocatalytic processes. Therefore, a visible-infrared active photocatalyst is the next level of demand for solving the alarming environmental issues. In this regard, the present article reports the investigations of crucial mechanisms and conditions leading to pure and defect-free hexagonal 2D CuSe nanosheets (NSs) and the influence of their structural architecture on visible-infrared active photocatalytic performance. Here, it was achieved by the conventional hydrothermal method by varying the pH of the reaction mixture. XRD analysis was used to examine the crystal structure and lattice parameters of CuSe NSs. The presence of H+ ions was suggested to significantly influence the observed anisotropic crystallite growth across different pH conditions. EDS and XPS analysis exhibited the purity and stoichiometry of 2D CuSe NSs, revealing that the obtained stoichiometry was consistent with CuSe composition. The morphological characteristics were investigated using FE-SEM as well as HR-TEM analyses, and the specific surface area was determined using Brunauer-Emmett-Teller analysis in which a significant change occurred in response to the variation in reaction conditions. The optical properties of optimized 2D CuSe NSs show excellent absorption in the visible and near-infrared region utilizing full solar with a notable decrease in emission intensity, suggesting a reduction in recombination rates due to pH-induced changes in the nanoarchitecture. Herein, methylene blue, a well-established model dye, was used as a probe to assess the photocatalytic activity of the synthesized CuSe NSs. Notably, the CuSe NSs synthesized under neutral conditions demonstrate a remarkable methylene blue degradation efficiency, reaching approximately 98 % within approximately 45 minutes, indicating a high degradation rate. Finally, an in-depth exploration into the intricacies of photocatalytic performance, degradation mechanisms, and the recyclability test was conducted, accompanied by a thorough investigation into the feasibility of CuSe NSs for their practical application in photocatalytic wastewater treatment.