Cubic Symmetry Research Articles

The Role of Chemical Pressure in the Formation of the Structure and Barocaloric Properties of Complex Fluorides and Oxyfluorides

The role of chemical pressure as an effective tool in the processes of formation of initial and distorted (as a result of structural transformations) phases, thermodynamic properties, and direct and inverse barocaloric effects in some complex oxyfluorides and fluorides with octahedral, tetrahedral, and spherical anion and cation groups in the structure has been studied. It is found that, due to the small temperature hysteresis and high baric sensitivity of materials, the maximum values of absolute and integral barocaloric characteristics can be implemented at low pressures. Correspondingly, the temperature range of reversibility of thermodynamic cycles based on fluorides/oxyfluorides as solid-state coolants can be expanded.

2M1 phlogopite–muscovite series minerals at increasing pressure to 9 GPa. I Atomic volumes and compressibilities

Muscovite (Ms) and phlogopite (Phl) series mineral is studied in the 2M1 polytype and modeled by the substitution of three Mg2+ cations in the three octahedral sites of Phl [KMg3(Si3Al)O10(OH)2] by two Al3+ and one vacancy, increasing the substitution up to reach the Ms [KAl2□(Si3Al)O10(OH)2]. The series was computationally examined at DFT using Quantum ESPRESSO, as a function of pressure from − 3 to 9 GPa. Crystal structure is calculated, and cell parameters, and geometry of atomic groups agree with experimental values. OH in the Mg2+ octahedrons are approximately perpendicular to the (001) plane, meanwhile when they are in Al3+, octahedral groups are approximately parallel to this plane. From Quantum Theory of Atoms in Molecules, the atomic basins are calculated as a function of the pressure, K+ and basal O show the largest volumes. The bulk excess volume (Vxs) and the excess atomic volumes are analyzed as a function of the composition and the pressure. K+, basal and apical O Vxs show a behavior similar to the bulk Vxs as a function of the composition, keeping qualitatively this behavior as a function of pressure; substituent atoms do not show a Vxs behavior similar to the bulk and their effect consequently is mostly translated to atoms in the interlayer space. Atomic compressibilities are also calculated. Atomic compressibilities are separated in the different sheets of the crystal cell. Atomic moduli of K and basal O are the lowest and the ones behaving as the bulk modulus of the series. The atomic bulk modulus of the H’s is different depending of their position with respect to the (001) plane.

Effect of laser repetition rate parameter in pulsed Laser ablation for synthesis Li4Ti5O12 polyether sulfone nanocomposite for optoelectronic applications

We examine Li4Ti5O12 (LTO) anode component inserted into PES produced by pulsed laser ablation in liquid media method with adjustable its particle size by tuning laser repetition rate, followed by post irradiation, to investigate the capability for using in Rechargeable lithium-ion batteries applications. Thermal analysis illustrates how material characteristics change with temperature. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), and energy dispersive spectra (EDS) are used to assess the compound's phase composition, optical characteristics, and elemental analyses. Without any usual peaks for other impurities, notably rutile and anatase TiO2, the XRD pattern showed a cubic spinel structure with high crystallinity of just LTO structure. The sample's component elements are confirmed by the EDS spectra since only the peaks for the impurities Ti and O could be seen in the spectra. FT-IR revealed that the broad absorption bands appeared at wave numbers in the figure print region because of the stretching vibrations of the octahedral groups (MO6) lattice. The XPS survey spectra reveal the presence of Li, Ti, O, C, and S. TGA revealed that the interaction of hydroxyl groups of PES with functional groups of LTO via hydrogen bonding may result in a temperature shift of breakdown. Electrical conductivity measurements were conducted at various frequencies and temperatures. The generated samples' real and imaginary parts of dielectric parameter characteristics were tested at frequencies ranging from 0.1 to 3 M Hz and temperatures ranging from 200 to 500 K. The temperature variation of the real component of the dielectric constant indicates that these compounds have high electromagnetic absorption and wideband electrical activity.

PtIV-Containing Hexaplatinate(II) [PtIVPtII6O6(AsO2(CH3)2)6]2- and Hexapalladate(II) [PtIVPdII6O6(AsO2(CH3)2)6]2.

The first PtIV-containing discrete polyoxoplatinate(II) [PtIVPtII6O6(AsO2(CH3)2)6]2- (Pt7) and polyoxopalladate(II) [PtIVPdII6O6(AsO2(CH3)2)6]2- (PtPd6) have been prepared and characterized in the solid state, in solution, and in the gas phase. The molecular structures of the noble metal-oxo clusters Pt7 and PtPd6 comprise a central, octahedral PtIVO6 hetero group surrounded by six square-planar MO4 (M = PtII, PdII) units, which are capped by six dimethylarsinate ligands. The polyanions were prepared under simple one-pot aqueous solution conditions by reacting H2Pt(OH)6 with either K2PtCl4 or Pd(NO3)2 in sodium dimethylarsinate buffer (pH 7) at 80 °C. Catalytic studies were performed on Pt7 supported on SBA15-apts for o-xylene hydrogenation at 300 °C and 90 bar H2 pressure and indicated excellent activity and recyclability with low activation temperature.

Effect of ZnO nanoparticles on physical, optical and radiation shielding properties of Bi2O3-B2O3-Cr2O3 glasses

With a composition (in mol %) of 29Bi2O3-70B2O3-(1-x)Cr2O3: xZnO, (where, x = 0, 0.5 and 1) three glass samples were prepared by melt-quenching process. Despite the addition of ZnO nanoparticles, the SEM- morphology studies showed that the synthesized samples were transparent glass-ceramics. XRD studies confirmed that ZnO nanoparticles were homogeneously distributed in the glassy phase. When ZnO nanoparticles were added, oxygen packing density (OPD) was observed to increase, whereas boron-boron separation (dB-B) gradually decreased. The Raman spectra demonstrated that there was transformation of primary glass forming units, [BO3] → [BO4] units from x = 0 to 1 mol% of ZnO nanoparticles in the composition. Two absorption bands (in blue and red regions) have been attributed to the d-d transitions of Cr3+ ions in octahedral symmetry sites. When ZnO nanoparticles were added in the composition, the bandgap (Eo) was found to increase, and the non-linear optical susceptibility (χ(3)) decreased. Various gamma ray shielding properties of the samples have been determined in the energy range of 1 keV–15 MeV with the help of the Windows based program EpiXS. The sample with highest concentration of ZnO nanoparticles in the composition showed better radiation shielding behaviour among the three samples.

Zn_{1-x}Ni_xTe semiconductor nanocrystals in transparent glass for optoelectronic device applications

Doping glass with semiconductors, particularly with nanostructured semiconductors, has attracted attention due to the large optical absorption cross-sections of the latter. Based on this property, Ni^{2+} (5 wt%) doped phosphate glass and Zn_{1-x}Ni_xTe (x = 0.5, 1.0, 5.0 and 10.0 wt% of Ni^{2+}) nanocrystals (NCs) doped phosphate glasses (GCs) were prepared by fusion method and subsequent heat treatment. Influence of Ni^{2+} on structural, thermo-optical and third-order nonlinear optical properties have been analysed through various spectroscopic characterizations. The XRD pattern of the glass (G) exhibits the amorphous nature of the host material while GCs exhibit not only amorphous halo but also the presence of quantum dots (QDs) or nanocrystals (NCs) phases. TEM analysis of the studied GCs samples confirm the presence of quantum dots (QDs) and bulk NCs with an average diameter of approximately 4.2 {pm } 0.3 nm and 13.4 {pm } 0.2 nm, respectively. Several phosphate groups were observed and reported from Raman and FTIR-ATR spectra. The absorption band positions confirmed that Ni^{2+} ions resemble to the octahedral symmetry. The intensity of absorption band around 1352 nm (^3T{_1}(F) rightarrow^3A{_2}(F)) increased with the increase of Ni^{2+} in GCs which is an indicative of the ^{[6]}Ni^{2+} coordination. The emission properties such as emission cross-sections ({sigma }_{emi}) full width at half maxima (FWHM) for the ^1T{_2}(D) rightarrow^3T{_2}(F) (visible) and ^3A{_2}(F) rightarrow^3T{_1}(F) (near-infrared) emission transitions were reported. Among the glass-containing semiconductor nanocrystals (GCs), the emission cross-sections in GC4 sample (x = 10% of Ni^{2+}) are the largest for both the visible (11.88 times 10^{-18} cm^2) and infrared (0.98 times 10^{-20} cm^2) transitions. Thermal diffusivity (D), thermal conductivity (K) and temperature dependent optical path length change (ds/dT) were obtained through time-resolved thermal lens (TL) and thermal relaxation (TR) methods. The D and K parameters do not change significantly with increase of Ni^{2+} ions (0.5–5%) in GCs. Nonlinear-refractive index and nonlinear absorption of the studied samples were also obtained using femtosecond Z-scan technique. The increase of nonlinear absorption coefficient (beta) is observed from GC2 (2.53 {times } 10^{-10} cm/W) to GC4 (7.98 {times } 10^{-10} cm/W). The GC4, sample with 10 wt% of Ni^{2+}, showed the lowest ds/dT (1.22 times 10^{-6} K^{-1}) with good lasing (FOM and emission cross-sections) and nonlinear absorption properties suggesting that it can be a good candidate for visible-red emission light conversion in LED technology.

Impactive cadmium modifications to enhance the structural-optical relationship in nickel borate glasses

Cadmium-doped borate glass composition was prepared via the melt-quenching technique. The nature of the glass structure was detected by X-ray diffraction (XRD). The physical parameters, such as density (ρ) from Archimedes’ principle, molar volume (Vm), Cd2+ ions concentration (NCd), and inter-atomic distance (Ri) were evaluated, providing structural information on glass samples. Fourier transform infrared (FT-IR) analysis was used to study the fundamental vibrational modes of structural units, confirming the conversion of BO3 to BO4 units, indicating a strongly bonded and high connectivity of the network. Some important optical findings were extracted from the analysis of optical absorption spectra. For example, the mitigation in the optical band gap, the increase in Urbach energy, the deterioration in the metallization criterion, and the enhancement in the electron-phonon interaction were obtained with cadmium oxide addition. The nonlinearity characteristics were enhanced, making these glass samples have viability in the non-linear optics sector. The obtained data from the electron spin resonance (ESR) revealed that the nickel ions exist in a divalent oxidation state with octahedral symmetry. Interestingly, the optical absorption transitions of Ni2+ ions were accurately deconvoluted and assigned to octahedral and tetrahedral positions. The equations of ligand field parameters of octahedral Ni2+ ions were correctly presented. The equation of Racah C parameter was deduced for the first time. Then, the ligand field parameters, such as the ligand field strength (10 Dq), Racah parameters (B and C), and other related parameters, were precisely assessed. The covalent nature between Ni2+ ions and the ligands was detected from the nephelauxetic effect.

Ligand field parameters, optical, thermal, magnetic, and structural features of ZnO containing cobalt-borate glasses

This article presents a study of cobalt speciation in borate glass samples, with up to 20 mol. % of zinc oxide. The samples were prepared by the melt-quenching method. The glass properties were presented utilizing a set of complementary investigations of all samples to evaluate structural, optical, thermal, and magnetic properties. XRD technique was exploited to scrutinize the structural nature of samples. Macrostructural modifications were demonstrated using Archimedes’ principle. FT-IR was utilized to probe the internal components of the glass network. Thermograms analysis was used to determine the thermal stability of the samples, which is required for applications. Optical band gap energy was decreased while the Urbach energy was enhanced. Using ligand field theory of cobalt ions, the optical absorption transitions were studied of Co2+ ions. Astonishingly, the usability of ligand field theory to evaluate the optical parameters was presented, in addition to their relation to the structural changes was demonstrated. Non-linearity aspects were enhanced with ZnO addition. Finally, ESR signals confirmed the existence of Co2+ ions in octahedral and tetrahedral symmetry, with a possibility of tetrahedral ions converting to octahedral symmetry. Based on the evaluation of ligand field parameters, besides the structural, optical, thermal, and magnetic features due to ZnO addition, our study reveals a significant potential for utilizing Zn-BNC glass for different optoelectronic purposes.

Effects of High Pressure on the Bandgap and the d–d Crystal Field Transitions in Wolframite NiWO4

The pressure effects on the optical and structural properties of NiWO4 have been studied experimentally and theoretically. The fundamental bandgap decreases with a pressure coefficient of −12.0 ± 0.2 meV/GPa. Meanwhile, the Ni2+ d–d transition energies increase at a rate of 7.4–14.8 meV/GPa. Therefore, the energy differences between the fundamental band and the Ni2+ d–d transition bands gradually decrease under pressure, which is beneficial to improve its optical performance. These optical phenomena are associated with structural variations. The shrinkage of the WO6 octahedron enhances the hybridization between the W 5d and O 2p orbitals, resulting in bandgap reduction. The pressure-induced enhancement of the NiO6 octahedral symmetry increases the crystal field splitting, thereby yielding increases in the Ni2+ d–d intraband transition energies. Besides, a pressure-induced structural phase transition is also observed around 20.0 GPa by both angle-dispersive synchrotron X-ray diffraction (ADXRD) and Raman experiments. This study provides valuable insight into the electron–lattice coupling of NiWO4 under compression and an effective way to modulate the electronic structure and optical properties of isomorphic wolframite materials.

BINARY HARD-SPHERE COLLOID-DROPLET MIXTURES WITH THE PYRITE-TYPE STRUCTURE

We investigate the assembly of a binary mixture of patchy colloids and droplets into crystal structures by use of the space-filling principle and Metropolis Monte Carlo simulations. Here, colloids with six patches in an octahedral symmetry attract droplets, whereas the colloid-colloid and droplet-droplet pairwise interactions are purely hard-core repulsions. Within parameter space regions that allow for stable binary crystals, we find the formation of different structure types, which are colloidal analogs of the NaCl phase and pyrite (FeS2) phase, as a function of the droplet-to-colloid sphere diameter ratio. This finding is consistent with theoretical predictions. Notably, while the NaCl structure type is a commonly known structure of hard-sphere colloids and nanoparticles, the formation of the FeS2 structure type from colloidal dispersion has not been explored. Our approach suggests a potential route to obtain colloidal crystals with more complex structures.

The Strong Effect of Fe on the Structural and Optical Properties of CdTiO3

Fe-doped Cadmium titanium oxide (CdTiO3) powders were prepared by the sol-gel method. The samples were characterised by Fourier-transform infrared (FTIR) spectroscopy, Electron paramagnetic resonance (EPR) technique, x-ray diffraction (XRD) and diffuse reflection spectroscopy (DRS). The X-ray diffraction results show well that all the samples displayed the ilmenite structure with the presence of minor traces of Titanium Dioxide (TiO2) and (Cadmium oxide) CdO phases, which ratio was shown to change with various concentrations in Fe. The estimated average particle size of the samples was around 56 nm. The photoluminescence properties of Fe-doped CdTiO3 were investigated. FTIR spectroscopy showed the presence of the Ti-O and CdO vibration bands. The spectra from the diffuse reflectance spectroscopy (DRS) DRS showed a red shift and a strong reduction of the gap energy compared to that of the pure sample (CdTiO3). The crystal structure of the CdTiO3 nano-powder presented a certain level of distortion due to the high concentration of oxygen vacancies. In fact, under (400) nm excitation, a clear green emission consecutive to oxygen vacancies was observed. The luminescence spectra of the Fe- doped CdTiO3 samples revealed that, due to oxygen vacancies, the emission and absorption intensities were both enhanced when the size was decreased. It can be inferred from our studies that the concentration of oxygen vacancies could be increased by reducing the crystallite size. The optical and ESR studies showed that the form of bivalent and trivalent states of iron were observed in distorted octahedral symmetry.

Probing the electrocatalytic activity of hierarchically mesoporous M-Co3O4 (M = Ni, Zn, and Mn) with branched pattern for oxygen evolution reaction

The large-scale production of hydrogen energy from the electrolysis of water requires earth-abundant and highly efficient oxygen evolution electrocatalysts. Cation substitution in spinel cobaltite is an efficient approach to tune electronic structure and improve their electrocatalytic activity towards oxygen evolution reaction (OER). In this article, for the first time, we have prepared hierarchically nanostructured Mn, Ni and Zn doped Co3O4 having a branching pattern via a simple hydrothermal and calcination method, and the same was used as an electrocatalyst for OER. Different methods confirmed the doping of transition metal ions. The result of structural characterization shows the formation of pure phase samples without impurity. The tetrahedral and octahedral functional groups were explained by FTIR spectroscopy, confirming the formation of a spinel structure. Ni-doped Co3O4 showed an excellent OER performance with a current density of 10 mA/cm2 at an overpotential of 380 mV in 1 M KOH and a Tafel slope of 63.19 mV/dec in alkaline media. The detailed study unveiled that the large surface area, hierarchically nanostructured branching pattern with porous structure, presence of a high amount of oxygen vacancy and the synergistic effect of Ni and Co are beneficial for increased OER activity and stability of Ni-Co3O4.

Triangulating Dopant-Level Mn(II) Insertion in a Cs2NaBiCl6Double Perovskite Using Magnetic Resonance Spectroscopy

Lead-free metal halide double perovskites are gaining increasing attention for optoelectronic applications. Specifically, doping metal halide double perovskites using transition metals enables broadband tailorability of the optical bandgap for these emerging semiconducting materials. One candidate material is Mn(II)-doped Cs2NaBiCl6, but the nature of Mn(II) insertion on chemical structure is poorly understood due to low Mn loading. It is critical to determine the atomic-level structure at the site of Mn(II) incorporation in doped perovskites to better understand the structure-property relationships in these materials and thus to advance their applicability to optoelectronic applications. Magnetic resonance spectroscopy is uniquely qualified to address this, and thus a comprehensive three-pronged strategy, involving solid-state nuclear magnetic resonance (NMR), high-field dynamic nuclear polarization (DNP), and electron paramagnetic resonance (EPR) spectroscopies, is used to identify the location of Mn(II) insertion in Cs2NaBiCl6. Multinuclear (23Na, 35Cl, 133Cs, and 209Bi) one-dimensional (1D) magnetic resonance spectra reveal a low level of Mn(II) incorporation, with select spins affected by paramagnetic relaxation enhancement (PRE) induced by Mn(II) neighbors. EPR measurements confirm the oxidation state, octahedral symmetry, and low doping levels of the Mn(II) centers. Complementary EPR and NMR measurements confirm that the cubic structure is maintained with Mn(II) incorporation at room temperature, but the structure deviates slightly from cubic symmetry at low temperatures (<30 K). HYperfine Sublevel CORrelation (HYSCORE) EPR spectroscopy explores the electron-nuclear correlations of Mn(II) with 23Na, 133Cs, and 35Cl. The absence of 209Bi correlations suggests that Bi centers are replaced by Mn(II). Endogenous DNP NMR measurements from Mn(II) → 133Cs (<30 K) reveal that the solid effect is the dominant mechanism for DNP transfer and supports that Mn(II) is homogeneously distributed within the double-perovskite structure.

2D Rhenium Dichalcogenides: From Fundamental Properties to Recent Advances in Photodetector Technology

AbstractVan der Waals (vdW) materials of transition metal dichalcogenides (TMD) family with semiconducting properties are currently at the forefront of research in the field of optoelectronics. The ability to couple them with one another at atomic interface precision in a synergistic way opens up unprecedented opportunities to design photodetectors of broad spectral range with excellent figures of merits not accessible to discrete materials. Recent years have seen a surge of interest in group VII TMD materials (ReS2 and ReSe2) due to their strong optical response from bulk to monolayer and good ambient stability. Their band gap energies spanning over visible and near‐infrared ranges and the strong linear polarization sensitivity stemming from the distorted octahedral symmetry, are ideally suited for polarization‐sensitive photodetectors. This review aims at providing a comprehensive understanding of the fundamental properties, optical identification of various structural features, long‐debated question of band gap nature and interlayer coupling, and recent advances in the development of photodetectors based on ReS2, ReSe2, and their vdW heterostructures with other layered materials of practical importance. We critically review various conceptual device designs implemented based on band engineering, emphasize on the merits of these photodetectors and their potential applications, and provide an outlook for future prospects.

Landau theory and self-assembly of spherical nanoclusters and nanoparticles with octahedral symmetry

Spherical nanoclusters and nanoparticles are rising materials whose functional design provides many useful applications ranging from catalysis, molecular sensing, gas storage to drug targeting and delivery. Here, we develop phenomenological crystallization theory of such spherical structures with octahedral symmetries O and O_h. Within the developed theory, we propose a method, which is based on constructing irreducible octahedral density functions and allows to predict the positions of structural units in the spherical nanoobjects. The proposed theory explains the structures of the simplest known metal nanoclusters, some metal-organic polyhedra and membrane protein polyhedral nanoparticles, and also predicts more complex chiral spherical structures and achiral assemblies characterized by the geometry of semiregular polyhedra. A relationship between the constructed irreducible octahedral functions and spherical lattices, obtained by mapping a plane hexagonal order onto a spherical surface through an octahedron net, is discussed as well.

Role of Local Structural Distortions on the Origin of j = 1/2 Pseudo-Spin State in Sodium Iridate

Na2IrO3 (NIO) is known to be a spin–orbit (SO) driven j = 1/2 pseudo-spin Mott–Hubbard (M–H) insulator. The mixing of j = 1/2 pseudo-spin derived from t2g orbitals with the eg orbitals has not been probed yet from the viewpoint of local structural distortions. Using a combination of theoretical calculations and X-ray spectroscopy, we show that the energetics in the vicinity of Fermi level (EF) is governed by SO interactions, electron correlation, and local octahedral distortions. The j = 3/2 and 1/2 pseudo-spin states have an admixture of both t2g and eg characters due to a local structural distortion. Reduction of the local octahedral symmetry also enables Ir 5d–O 2p hybridization around the EF resulting in an M–H insulator with enhanced charge-transfer character. The possibility of the Slater insulator phase is also ruled out by a combination of the absence of room-temperature density of states in valence band spectra, calculated moments, and temperature-dependent magnetization measurements.

Shannon Information Entropy Sum of a Free Particle in Three Dimensions Using Cubical and Spherical Symmetry

In this paper, the plane wave solutions of a free particle in three dimensions for Cubical and Spherical Symmetry have been considered. The coordinate space wave functions for the Cubical and Spherical Symmetry are obtained by solving the Schrdinger differential equation. The momentum space wave function is obtained by using the operator form of an observable in the case of Cubical Symmetry. For Spherical Symmetry, the same is obtained by taking the Fourier transform of the respective coordinate space wave function. The wave functions have been used to constitute probability densities in coordinate and momentum space for both the symmetries. Further, the Shannon information entropy has been computed both in coordinate and momentum space respectively for (L is the length of the side of the cubical box) values for Cubical Symmetry and for values in Spherical Symmetry keeping (k is the wave vector and p is the momentum of the free particle) constant. The values obtained for the Shannon information entropies are found to satisfy the Bialynicki-Birula and Myceilski (BBM) inequality at larger values () in case of Cubical Symmetry and for values of and in Spherical Symmetry.

Bandgap modification in 0D tellurium iodide perovskite derivatives via incorporation of polyiodide species.

Halide perovskites provide a versatile platform for exploring the effect of non-covalent interactions, including halogen bonding, on material properties such as band gap, luminescence, and frontier orbital landscape. Herein we report six new zero-dimensional tellurium iodide perovskite derivatives, consisting of [TeI6]2- octahedra charge balanced by one of several X-Py cations (X = H, Cl, Br, I, and Py = pyridinium). These compounds also feature robust halogen bonding between [TeI6]2- octahedra and polyiodides in the form of I2 (1-4), I3 - (5), or adjacent octahedra (4 and 6). These relatively strong non-covalent interactions (NCIs) are modeled by natural bond order (NBO) and second order perturbation theory (SOPT) calculations. NCIs are responsible for reducing the bandgap of these materials (measured via diffuse reflectance spectroscopy) relative to those without polyiodide species. They also affect inner sphere bonding in the metal halide, exacerbating [TeI6]2- octahedron asymmetry as compared to previously published compounds, with greater asymmetry correlating with higher van der Waals overlap of halogen-halogen contacts. We also demonstrate the ability of hydrogen and carbon bonding (which dominates in the absence of polyiodides) to affect inner sphere tellurium iodide bonding and octahedral symmetry.

Broad intrinsic luminescence properties in Nb4TeO12 mixed-metal niobate tellurite

Mixed-metal oxides composed of Nb5+(d0) and Te4+(p-) cations generally exhibit excellent optoelectronic properties due to the stereoactive lone pair of electrons in the structure. In this work, a mixed-metal niobate tellurite Nb4TeO12 was prepared using solid state reaction method. The polycrystalline samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), optical absorption, photoluminescence (PL) and dynamic properties. This sample shows characteristic indirect electronic transitions with an interband energy of 3.01 eV. The bottom of conduction band and the top of valence band are +0.37 eV and +3.38 eV, respectively. Using a Nd:YAG pulsed laser as the excitation light source, the intrinsic luminescence of Nb4TeO12 was investigated over a wide temperature range of T = 10–300 K. The broad band emission peaking at 513 nm corresponds to the self-activating luminescence of the niobate octahedral group [NbO6]7−. The luminescence decay curve did not depend on the laser excitation energy, and it showed a non-exponential characteristic with two decay lifetime components. The experiments also preliminarily studied the performance of the luminescence application of Nb4TeO12.

Activation-induced layered structure in NiCoAl by atomic modulation for energy storage application

The surface activation of alloys favors their electrochemical interactions, ion diffusivity, and the rapid kinetics of ions and electrons, leading to the formation of self-supported layered double hydroxides (LDHs) in them. However, the formation of LDHs at different depths in the alloy upon activation, their electronic/atomic structures, and their electrochemical charge storage mechanism, have not been thoroughly explored. Herein, Ni ion-substituted CoAl alloys are prepared by arc melting and activated by KOH electrolyte, which is responsible for the modulation of the atomic configuration as confirmed by XRD. Raman depth mapping demonstrates how the LDHs vary with depth upon activation and that the octahedral and tetrahedral symmetry sites of CoO and Co3O4 are responsible for the formation of the layered structures of CoOOH and Co(OH)2, respectively. The activated Ni10Co85Al5 has a superior volumetric capacitance of 4.15 F/cm3 at 0.5 mA/g, which is 38.6 times that of an unactivated one, and excellent cyclic stability up to 5000 cycles, and a voltage of 0.54 V generated from a fabricated supercapacitor cell. X-ray Absorption Spectroscopy (XAS) analysis indicates greater charge transfer by Co than by Ni and the modulation of the local atomic structures facilitates electrochemical charge storage in Ni10Co85Al5. This work presents an easy route for the development of advanced LDHs, and the mechanism of electrochemical charge storage in them.