Host Crystal Structure Research Articles

A Comparative Study of Congo Red Textile Dye Photodegradation Using ZnO Al and ZnO Al+Mn Nanoparticles

Photodegradation of Congo Red textile dye was successfully carried out using ZnO Al and ZnO Al+Mn nanoparticles synthesized using the bottom-up coprecipitation method. Powder X-ray diffraction provides information that Al and Mn doping successfully inserted in the host crystal structure while maintaining the Hexagonal Wurtzite crystal structure. However, a shift in the diffraction peak caused by the lattice distance changes with the addition of doping. FE-SEM EDS provides information that both nanoparticles are nonuniform sphere-like due to the addition of dopping, and each dopping is detected through EDS spectra. There is a decrease in the gap energy in each sample. ZnO Al nanoparticles have a gap energy of 3.29 eV, and ZnO Al+Mn nanoparticles have a gap energy of 3.28 eV. However, the decrease in the gap energy is not directly related to the percentage and kinetic rate of Congo Red photodegradation. Adding 5 mg of ZnO Al Nanoparticles powder could degrade Congo Red up to 97.9 % within 120 min using UV A radiation or 0.03504/min. At the same time, adding ZnO Al+Mn Nanoparticles powder with the same parameters could only degrade 67.6 % or 0.00759/min. HIGHLIGHTS Energy Bandgap Modification of ZnO Nanoparticles The incorporation of Al single dopants and Al, Mn co-dopants into ZnO nanoparticles synthesized via a bottom-up coprecipitation method significantly alters the energy bandgap. Al single doping resulted in a bandgap of 3.29 eV, while Al, Mn double doping yielded a bandgap of 3.28 eV. Enhanced Photocatalytic Activity of Al-Doped ZnO Al-doped ZnO nanoparticles exhibited superior photocatalytic activity toward the degradation of Congo Red textile dye. With a photodegradation rate constant of 0.03504 min⁻¹, these nanoparticles achieved 97.9 % degradation of Congo Red within 120 minutes. Comparative Photocatalytic Performance of Al, Mn Co-Doped ZnO While Al, Mn co-doped ZnO nanoparticles were synthesized using the same method, their photocatalytic performance for Congo Red degradation was notably lower than that of Al-doped ZnO. The calculated photodegradation rate constant was 0.00759 min⁻¹, resulting in 67.6 % degradation within the same timeframe. GRAPHICAL ABSTRACT

Challenges and Progress in Rechargeable Magnesium‐Ion Batteries: Materials, Interfaces, and Devices

AbstractRechargeable magnesium‐ion batteries (RMBs) have garnered increasing research interest in the field of post‐lithium‐ion battery technologies owing to their potential for high energy density, enhanced safety, cost‐effectiveness, and material resourcefulness. Despite substantial advancements in RMB research, a number of intrinsic challenges remain unresolved, such as the strong Coulombic interaction between Mg2+ and the host crystal structure of cathode materials, sluggish Mg2+ diffusion kinetic, poor electrolyte compatibility, and the formation of passivation films on the Mg anode interface. These issues hinder the commercial applications of RMBs. This review provides a comprehensive overview of the progress in key areas of RMB research, including representative magnesium‐ion storage cathode/anode materials and magnesium‐ion conducting electrolytes. Additionally, recent developments in electrode‐electrolyte interface regulations and pouch‐cell fabrication are outlined, highlighting current challenges and the implementation of effective solutions. Finally, future research directions are proposed to guide the development of high‐performance RMBs with practical applications.

Molecular Origins of Near-Infrared Luminescence in Molybdenum and Tungsten Oxyhalide Perovskites.

Materials with near-infrared (near-IR) luminescence are desirable for applications in communications and sensing, as well as biomedical diagnostics and imaging. The most used inorganic near-IR emitters rely on precise doping of host crystal structures with select rare-earth or transition metal ions. Recently, another class of materials with intrinsic near-IR emission has been reported. The compositions of these materials were initially described as vacancy-ordered halide double perovskites Cs2MoCl6 and Cs2WCl6, but further investigation by some of us on the compound reported as Cs2WCl6 revealed an oxyhalide instead, with a composition Cs2WO x Cl6-x , where 1 < x < 2. Here we demonstrate that the Mo compounds similarly possess the composition Cs2MoO x Cl6-x or Cs2MoO x Br6-x where 1 < x < 2. Preparing the pure halide appears harder for Mo than for W, and we have not succeeded in doing so. The distinctly different composition requires the coordination environment and oxidation state for the Mo and W centers to be reconsidered from what was assumed for the pure halides. In this work, we examine the mechanism for near-IR emission in these materials given their true structures and compositions. We demonstrate that the luminescence is due to the specific d-orbital splitting caused by the presence of oxygen in the distorted [MOX5]2- octahedra (X is Cl or Br). The fine structure in the emission spectra at low temperatures has been resolved and is attributed to vibronic coupling to the Mo-O and W-O bond stretches. Understanding the true structure and composition of these interesting materials, besides explaining the near-IR luminescence, suggests how this desirable emission can be realized and manipulated.

Niobate Anodes for High Rate Lithium-Ion Batteries

Fast charging is one of the key performance requirements for next generation lithium ion batteries, and is directly related to the ease of ionic and electronic transport. However, lithium ion diffusion rates of promising anode materials, such as Li4Ti5O12, anatase TiO2, T-Nb2O5 and Nb18W16O93, are still insufficient. Therefore, nanosizing of the active electrode material is a common strategy to increase the effective lithium ion diffusion transport rate, which unfortunately also decreases the volumetric energy/power density and stability of the battery.Recently, we demonstrated nickel niobate, NiNb2O6, for the first time as a new intrinsic high-rate electrode material,[1] which exhibits an intrinsic high rate performance enabled by its suitable host crystal structure without the requirement of realizing nano-architectures. The NiNb2O6 host crystal structure exhibits only a single type of channel for lithium ion intercalation and can be fully lithiated up to Li3NiNb2O6 with a capacity of about 244 mAh/g at low current densities. Interestingly, a high diffusion coefficient of 10-12 cm2/s at 300 K enables fast (dis)charging at high current densities resulting in high capacities of 140 and 50 mAh/g for respectively 10C and 100C. The minimal volume change during lithiation is the origin of the stable reversible lithiation process in NiNb2O6 and leads to a capacity retention of 81% after 20.000 cycles at 100C. The structural stability and electrochemical behaviour were investigated by various experimental techniques and confirmed by density functional theory (DFT) calculations. Finally, full cell systems against LiFePO4 and NCM811 cathodes demonstrate the promising energy storage performance of nickel niobate anodes in practical battery devices.Our results strongly suggest that niobate-based materials are intrinsic high-rate anode materials without the requirement of realizing nano-architectures as typical for numerous titanium- and niobium-based oxides through complex synthesis procedures to minimize the length scales for lithium diffusion. Recently, we have replaced nickel by other transition metal ions to widen the exploration of niobate compounds for fast lithium ion diffusion. Large variations in electrochemical performance are observed, and the latest results will be presented. This will provide a new perspective on the role of intrinsic high-rate electrode materials for realizing ultrafast anode materials for future energy storage devices.[1] R. Xia et al., Advanced Energy Materials 12 (2022) 2102972.

Thermally Promoted Cation Exchange at the Solid State in the Transmission Electron Microscope: How It Actually Works.

Cation exchange offers a strong postsynthetic tool for nanoparticles that are unachievable via direct synthesis, but its velocity makes observing the onset of the reaction in the liquid state almost impossible. After successfully proving that cation exchange reactions can be triggered, performed, and followed live at the solid state by an in situ transmission electron microscopy approach, we studied the deep mechanisms ruling the onset of cation exchange reactions, i.e., the adsorption, penetration, and diffusion of cations in the host matrices of two crystal phases of CdSe. Exploiting an in situ scanning transmission electron microscopy approach with a latest generation heating holder, we were able to trigger, freeze, and image the initial stages of cation exchange with much higher detail. Also, we found a connection between the crystal structure of CdSe, the starting temperature, and the route of the cation exchange reaction. All the experimental results were further reviewed by molecular dynamics simulations of the whole cation exchange reaction divided in subsequent steps. The simulations highlighted how the cation exchange mechanism and the activation energies change with the host crystal structures. Furthermore, the simulative results strongly corroborated the activation temperatures and the cation exchange rates obtained experimentally, providing a deeper understanding of its phenomenology and mechanism at the atomic scale.

Cation-defect-induced self-reduction towards efficient mechanoluminescence in Mn2+-activated perovskites.

Mechanoluminescent (ML) materials have shown promising prospects for various applications, e.g. in stress sensing, information anti-counterfeiting and bio stress imaging fields. However, the development of trap-controlled ML materials is still limited, because the trap formation mechanism is not always clear. Here, inspired by a defect-induced Mn4+ → Mn2+ self-reduction process in suitable host crystal structures, a cation vacancy model is creatively proposed to determine the potential trap-controlled ML mechanism. Combined with the theoretical prediction and experimental results, both the self-reduction process and ML mechanism are clarified in detail, where the contribution of and defects dominates the ML luminescent process. Electrons/holes are mainly captured by the anionic/cationic defects, followed by the combination of electrons and holes to transfer energy to the Mn2+ 3d states under mechanical stimuli. Based on the multi-mode luminescent features excited by X-ray, 980 nm laser and 254 nm UV lamp, together with the excellent persistent luminescence and ML, a potential application in advanced anti-counterfeiting is demonstrated. These results will deepen the understanding of the defect-controlled ML mechanism, and inspire more defect-engineering strategies to develop more high-performance ML phosphors for practical application.

Analysis of site symmetries of Er3+ doped CaF2 and BaF2 crystals by high resolution photoluminescence spectroscopy

The understanding of complex relationships between luminescent properties, local symmetry of an emitting center, and the host crystal structure provides a better insight into optical properties of materials. In this work, the alkaline earths CaF2 and BaF2 fluoride crystals doped with 0.1 mol% ErF3 were investigated. The crystals structure has been studied using a synchrotron and laboratory X-ray diffraction. The C3v and C4v sites symmetry were determined using erbium probed high resolution emission spectroscopy (HRPL) at low temperature (LT) of 10 K. The considerable difference in room temperature (RT) optical properties for CaF2 compared to BaF2 crystals was observed. Such difference in absorption intensity of 4.7 times of erbium 4G11/2 manifold in UV, and 7.5 times in green emission from 4S3/2 manifold, could be due to the distinction in the host crystals cationic radius (ΔrCa,Ba) and the dopant-host ionic radius (ΔrCa-Er, ΔrBa-Er). Those Δr differences influence the structure and lead to the following symmetry formation: In CaF2, the C4v and C3v isolated centers were identified, with the determined Er3+- F−i bond lengths of 2.734 Å and 4.735 Å respectively; In BaF2, only C3v isolated centers were identified with the determined Er3+- F−i bond lengths of 5.380 Å. The present work is the first study that takes into account correlations of optical properties, the local symmetry and the structure in mentioned fluorides crystals, and it could be a step forward in the lanthanide doped optical materials systematics.

Front Cover: Enhanced Host‐Guest Association and Fluorescence in Copolymers from Copper Salphen Complexes by Supramolecular Internalization of Anions (ChemPlusChem 3/2023)

The cover picture shows a fluorescent Cu-Salphen host crystal structure interacting with an anion guest pink sphere that emits in the yellow-green region represented by fireflies, as well as the counterparts linked to a polymer chain represented as a blue ribbon, which yields blue-shifted hyperchromic cyan luminescence due to the protection from its coil conformation. They emerge from the UNESCO's World Heritage Site Central University City Campus of the National Autonomous University of Mexico. More information can be found in the Research Article by G. Zelada-Guillén, M. V. Escárcega-Bobadilla, and co-workers.

Zaltoprofen-layered double hydroxide hybrids to enhance zaltoprofen solubility and dissolution rate

The zaltoprofen-LDH hybrid was successfully synthesized by coprecipitation method, and its dissolution profile and solubility in different fluids, that simulate the gastro-intestinal environment, were investigated. The zaltoprofen-LDH hybrid stoichiometry was determined by EDS and TGA, and the Zn0.70Al0.30(OH)2Z0.30·0.76H2O chemical formula was obtained, which well compares to the Zn/Al molar ratio of the pristine LDH (nitrate-LDH hybrid: Zn0.73Al0.27(OH)2(NO3)0.27·0.44H2O), synthesized to prepare the zaltoprofen-LDH physical mixture for the dissolution tests. The XRPD results confirmed the successful insertion of the zaltoprofen in the interlayer space of the LDH structure: the 003 reflection, detected at d-value of 8.7 Å in the pristine LDH, was observed at d-value of 21.8 Å, and the drug occupied a gallery of about 17 Å. Based on the zaltoprofen size (9.9 × 4.9 Å), a drug arrangement in which the molecules form a monolayer of partially superimposed drug anions into the brucite-like layer is suggested. The DSC peak due to the melting process of the pure zaltoprofen was not observed in the zaltoprofen-LDH hybrid, thus indicating the loss of the long-range structural order in the active principle. FT-IR spectroscopy confirmed that the zaltoprofen entered the host structure in the anionic form (COO−). Deep insights in the drug-LDH interaction were obtained by 13C and 27Al solid state NMR: the zaltoprofen molecules strongly interacted with the LDH layers involving the COO- and the OH moieties respectively, while the packing of the drug molecules in the layers was comparable to the conformation of the pure zaltoprofen crystals. The zaltoprofen anion insertion caused local structural changes within the host crystal structure. The solubility and dissolution tests, performed on the synthesized hybrid and compared to the pure zaltoprofen and zaltoprofen-LDH physical mixture, demonstrated enhanced solubility and dissolution rate of the drug in the hybrid system.

Tetravalent Doping in Fluorite-Based Ferroelectric Oxides for Reduced Voltage Operations.

First-principles calculations show a reduced energy barrier for polarization switching via a bulk phase transition by doping of hafnium-zirconium oxide (HZO). The tetragonal P42/nmc phase serves as a transition state for polarization switching of the polar orthorhombic Pca21 phase. Due to the high symmetry of the tetragonal phase, dopants can form more energetically favorable local oxygen bonding configurations in the tetragonal phase versus the orthorhombic phase. Significant bond strain is observed in the orthorhombic phase due to the low symmetry of the host crystal structure which decreases the relative stability of the doped orthorhombic phase compared to the doped tetragonal phase, thereby significantly lowering the barrier for switching but slightly affecting the polarization of the orthorhombic phase. Si is a promising dopant for an efficient ferroelectric device with minimal disturbance in the electronic structure parameters. Ge doping is suitable for stabilizing the tetragonal phase which shows a high k value.

Order and disorder in the modulated phase hp‐Mg9Ge5.1

AbstractSingle crystals of Mg9Ge5.1(2) were obtained at a pressure of 5 GPa in the temperature range 723 to 1273 K. The metastable high‐pressure phase exhibits a crystal structure, which may be described as a host‐guest variety of an UCl3‐type framework. The atomic arrangement is characterized by a host crystal structure Mg9Ge3 with disordered germanium guests (≈2 Ge per formula unit) in the channels. The composite arrangement undergoes incommensurate modulation. Upon heating at ambient pressure, the phase transforms into the thermodynamically stable compounds Mg2Ge and Ge at 496(5) K. Measurements of the magnetic susceptibility indicate diamagnetic behavior between 75 and 350 K.

Boron induced c-axis growth and ammonia sensing signatures of spray pyrolysis deposited ZnO thin films – Relation between crystallinity and sensing

Boron (B) doping in zinc oxide (ZnO) using spray pyrolysis has always led to deterioration of host crystal structure. Unlikely, here, we report the optimized spray pyrolysis deposition parameters for the development of c-axis oriented boron-doped ZnO thin films. As the B concentration increases from 2 to 10 mol%, the hexagonal crystal structure exhibited a highly oriented (002) plane with an increased texture co-efficient. In particular, 2 mol% B dopants promoted the growth of the (101) and (100) planes and increased the crystallite size. Tensile stress in the c-axis plane of 10 mol% B-doped ZnO films leads to the red shift in the band gap (from wide to narrow). Furthermore, 10 mol% B dopants resulted in the enhanced ammonia sensing performance at room temperature. The sensing performance of all the deposited B-doped ZnO films revealed that influence of enhanced planes of host structure energetically favoured the ammonia adsorption.

Role of crystal water in luminescence properties of copper-doped hydronium alunite

Copper-doped hydronium alunite [(H3O)Al3(SO4)2(OH)6:Cu], a novel luminescent sulfate material, exhibiting blue luminescence was successfully synthesized under hydrothermal conditions. The originality of this luminescent material is such that the host crystal structure consists of crystal water (hydronium ions and hydroxyl radicals). Herein, we reported the results of a detailed investigation of changes in luminescence characteristics of the material with heat treatments. It was found that the material’s emission intensity was significantly reduced by heat treatment at temperatures ≥318 °C. The effect of varying amounts of copper and the extent of dehydration on the emission intensity was also investigated. As a result, a clear tendency was obtained that the luminescence intensity decreased as the weight loss increased due to dehydration. Thus, the presence of copper and crystal water are important factors affecting the luminescence of the material.

Nickel Niobate Anodes for High Rate Lithium‐Ion Batteries

AbstractFast charging is one of the key requirements for next‐generation lithium‐ion batteries, however, lithium‐ion diffusion rates of typical electrode materials are limited. Nanosizing of active electrode material is a common strategy to increase the effective lithium‐ion diffusion transport rate, but it also decreases the volumetric energy/power density and stability of the battery. In this work, nickel niobate NiNb2O6 is demonstrated for the first time as a new intrinsic high‐rate anode material for lithium‐ion batteries without the requirement of realizing nano‐architectures. The NiNb2O6 host crystal structure exhibits only a single type of channel for lithium‐ion intercalation and can be fully lithiated with a capacity of about 244 mAh g−1 at low current densities. Interestingly, a high diffusion coefficient of 10−12 cm2 s−1 at 300 K enables fast (dis)charging at high current densities resulting in high capacities of 140 and 50 mAh g−1 for 10 and 100C respectively. The minimal volume change during lithiation is the origin of the stable reversible lithiation process in NiNb2O6 and leads to 81% capacity retention after 20 000 cycles at 100C. Finally, full cell systems against LiFePO4 and Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathodes demonstrate the promising energy storage performance of nickel niobate anodes in practical battery devices.

Dilute Element Compounds: A Route to Enriching Inorganic Functional Materials.

The development of functional materials calls for ever-enriching the inorganic material database. Doping is an effective way of achieving this purpose. Herein, we propose the concept of dilute element compounds (DECs), which contain a small amount of a dopant element distributed in a host crystal structure in an ordered manner. Different from dilute alloys or solid solutions, the DECs could be more resistant to segregation and are ideal for dispersing functional elements for applications such as single-atom catalysts. It is also expected that the DECs will serve as a route to discovering new inorganic functional materials by controlling phase transitions and tuning intrinsic properties of the host materials with applications including, but not limited to, thermoelectrics and solid-state electrolytes for secondary batteries. As an initial work, we quantify the diluteness of DECs and find the limits of diluteness in existing DECs. We further provide a classification scheme for the DECs to guide future discoveries.

Suppressing ion migration of CsPbBr x I3-x nanocrystals by Nickel doping and the application in high-efficiency WLEDs

All inorganic perovskite nanocrystals CsPbX3(X = Cl, Br, I) are the great potential candidates for the application of high-performance light emitting diodes (LED) due to their high Photoluminescence Quantum Yield (PLQY), high defect tolerance, narrow full-width half-maximum and tunable wavelength of 410–700 nm. However, the application of red-emitting (630–650 nm) CsPbBr x I3-x nanocrystals are perplexed by phase segregation due to the composition of mixed halides and the difference in halide ion mobility. Herein, we provide an effective strategy to suppressing the migration of Br/I ions through Ni2+ doping via a facile Hot-Injection method and the PLQY was improved as well. DFT calculations show that the introduction of Ni2+ causes a slight contraction of the host crystal structure, which improves the bond energy between Pb and halides and reduces the level of surface defects. Therefore, the phase stability is improved by Ni2+ doping because the phase segregation caused by ion migration in the mixed phase is effectively inhibited. Meanwhile, the non-radiative recombination in the exciton transition process is reduced and the PLQY is improved. What’s more, benefiting from the suppressed ion migration and enhanced PLQY, we combine the Ni2+-doped CsPbBr x I3-x nanocrystals with different Br/I ratios and YAG: Ce3+ phosphors as color conversion layers to fabricate high efficiency WLED. When the ratio of Br/I is 9:11, WLED has a color coordinate of (0.3621, 0.3458), the color temperature of 4336 K and presents a high luminous efficiency of 113.20 lm W−1, color rendering index of 94.9 under the driving current of 20 mA and exhibits excellent stability, which shows great potential in the application of LED.

An Ab Initio Perspective on the Key Vacancy Defects of KMgF3

Perovskite-type KMgF3, which represents a distinct class of multifunctional materials, has drawn immense interest in the advanced technological fields due to its various attractive properties. However, these properties are strongly influenced by the presence of various vacancy point defects in the host crystal structure. This drives us to gain a detailed knowledge of the defect chemistry in KMgF3 by investigating geometry, electronic structure, defect formation energies, and charge transition levels. To achieve reliable results, we have adopted hybrid density functional calculations. To find out the stable growth condition for all possible vacancy defects and vacancy cluster defects in KMgF3, calculations of defect formation energies under different chemical potential range have been carried out. Among all the vacancy defects considered in this study, the calculated formation energy for VMg in a −2 charge state is found to be a more negative value as the Fermi energy level approached toward the conduction band minimum irrespective of the chemical potential range. The present study explored the role of different vacancy defects in creating impurity states in the band gap region by detailed analysis of electronic structure in each case. It has been observed that the impact of anion vacancy and their aggregation on the electronic structure of KMgF3 is much more prominent than that of cation vacancy. The electrical and optical properties of KMgF3 in the presence of various defects have been described on the basis of calculated thermodynamic and optical charge transition levels, respectively. It has been revealed that the cation vacancy defects are not likely to form deep defect states, while anion vacancy and their aggregation act as deep donor defects. The mixed cluster vacancy of K and F pair behaves differently with respect to Mg and F pair in the optical property. The cation vacancies have hardly any contribution to the observed optical spectrum, which is consistent with experimental observation. Thus, an unambiguous and ultimate clarification of the fundamental absorption and emission processes in KMgF3 has been accomplished in the present study.

Preparation of neodymium‐doped LiMnPO 4 /C cathode by sol‐gel method with excellent electrochemical performance for lithium‐ion batteries

The porous spherical structure neodymium-doped LiMn1−xNdxPO4/C nanoparticles have been prepared through glycolic acid-assisted sol-gel method. The neodymium-ion doping effect on the crystalline microstructure, crystal appearance, and electrochemical parameters of LiMnPO4/C cathodes have been detected by X-ray diffractometer (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), charge and discharge test, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) method. XRD patterns show that a proper amount of neodymium-ion doping could not change the host crystal structure; combined with EDS spectra, we could conclude that Nd3+ has successful embedding into the lattice structure of LiMnPO4/C. SEM analysis shows that the LiMn0.94Nd0.06PO4/C sample has the uniform and fine particles diameter distribution in comparison with other doped samples. The electrochemical measurement results indicate that the LiMn0.94Nd0.06PO4/C has the initial discharge specific capacity of 155.2 mAh/g at 0.05 C discharge rate; after 200 cycles, the capacity value reduces slightly to 138.7 mAh/g, the capacity retention rate is maintained at 89.4%. The LiMn0.94Nd0.06PO4/C has high-rate discharge performance with the specific capacity value of 128.0 mAh/g (10 C). The results conclude that a proper amount of neodymium-ion doping ratio could effectively enhance the lithium-ion diffusivity and improve high-rate performance of LiMnPO4 cathode materials.

EXAMINATION OF VANADIUM EFFECT ON GENERAL MECHANICAL CHARACTERISTICS OF Bi-2223 MATERIALS VIA SEMI-EMPIRIC MODELS

In the current work, we semi-empirically investigate the load-independent Vickers hardness values of vanadium added Bi-2223 compounds in the plateau limit regions evaluated from the experimental microhardness graphics (Vickers hardness parameters versus applied indentation test loads) to determine the role of vanadium particles on the general mechanical characteristics with the aid of six mechanical modeling approaches, namely law of Meyer, proportional sample resistance, elastic/plastic deformation, modified proportional sample resistance, Hays-Kendall and indentation-induced cracking models. Throughout the study, the samples are prepared with the different molar rations varying from x=0 to 0.3 by the conventional ceramic method in the normal atmospheric pressure at the room temperature conditions. All the model findings show that the mechanical performances tend to constantly reduce with increasing the vanadium concentration level embedded in the Bi-2223 superconducting crystal system. This is in accordance to the fact that the concentration level of vanadium remarkably damages the main structural problems and permanent irreversible deformations. In this respect, it is not wrong to verify that the vanadium inclusions unstabilize the inherit durable tetragonal phase of Bi-2223 inorganic solids, resulting in the regression in the mechanical durability (resistance towards to the applied loads) in case of the applied test loads. Moreover, the models indicate that every material prepared exhibits the conventional indentation size effect (related to the formation of elastic and plastic deformations in the host crystal structures simultaneously due to the recovery of systems) but within the suppression trend. Shortly, all the semi-empiric models preferred in the present work are found to be useful descriptors to define the suitable relationship between the ion-addition mechanism in the crystal lattice and mechanical durability/performances of vanadium-added Bi-2223 materials. We should, of course, declare here that Hays–Kendall approach is gathered to be the best approach model for the load-independent Vickers hardness values in the plateau limit regions.

Elucidating Reversible Electrochemical Anionic Redox in Intercalation Electrodes for Rechargeable Multivalent-Ion Batteries

Battery electrodes that enable electrochemical intercalation of multivalent ions result in multiple electron transfers per ion, respectively, yielding significant enhancements in electric charge storage capacity. When multivalent cathodes are paired with their corresponding metal anodes, potentially transformative gains in energy density are possible. However, few positive electrode materials exist that intercalate multivalent ions, in part due to the slow solid-state diffusion of highly charged multivalent ions. The chevrel phases Mo6X8, where X is a chalcogen atom (e.g., S or Se) are among the few materials known to reversibly and electrochemically intercalate both divalent (e.g. Mg2+, Zn 2+, etc.) and trivalent (Al3+) ions. Thus, understanding the ion intercalation and electron charge transfer mechanisms within these unique compounds may provide insights into the molecular-level design of new intercalation electrodes for rechargeable multivalent ion batteries.Here, we couple electrochemical and solid-state magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) measurements to reveal the concurrent aluminum-ion intercalation and electron charge transfer mechanisms in chevrel electrodes Mo6S8 and Mo6Se8 up from the molecular level. Solid-state 27Al single-pulse MAS NMR measurements were performed on the thio-chevrel Mo6S8 electrodes at different states-of-charge to observe changes in the environments and to quantify the local populations of aluminum ions within the host crystal structure, revealing both intercalated ions and additional aluminum species associated with surface layers and/or decomposition products. Al-Mo6Se8 batteries were made for the first time and their electrochemical properties were compared to the thio-chevrel Mo6S8. Solid-state 77Se and 95Mo MAS NMR measurements on the seleno-chevrel Mo6Se8 at charged and discharged states revealed that electrons are transferred preferentially to the anionic chalcogen framework upon aluminum ion intercalation, as opposed to the transition metals (Mo). Anionic redox was further confirmed by density functional theory (DFT) calculations and X-ray absorption near-edge structure (XANES) measurements. Lastly, we generalize the results to other ion valencies, demonstrating reversible electrochemical anionic redox in the Chevrel phase upon divalent Zn2+ cations in aqueous Zn batteries.Overall, for the first time, we demonstrate reversible electrochemical anionic redox as a charge storage mechanism for rechargeable batteries, which preserves the crystalline framework structure and does not involve the breaking and forming of chemical bonds. This charge storage mechanism is fundamentally different than that observed for lithium-ion intercalation into transition metal oxides, where the electrons are stored within the d-orbitals of the transition metal. The results suggest materials design principles aimed at designing multivalent-ion intercalation electrodes with improved electrochemical properties. Figure 1