Neutron Powder Diffraction Patterns Research Articles

Magnetic symmetries of terbium tetraboride (TbB4) revealed by resonant x-ray Bragg diffraction

A recent experimental study of TbB4 at a low temperature using resonant x-ray Bragg diffraction implies a magnetic symmetry not found in any other rare-earth tetraboride. The evidence for this assertion is a change in the intensity of a TbB4 Bragg spot on reversing the handedness (chirality) of the primary x-ray beam [R. Misawa, K. Arakawa, T. Yoshioka, H. Ueda, F. Iga, K. Tamasaku, Y. Tanaka, and T. Kimura, ]. It reveals a magnetic chiral signature in TbB4 that is forbidden in phases of rare-earth tetraborides known to date, as the previous magnetic symmetries are parity-time (PT) symmetric with anti-inversion present in the magnetic crystal class. Misawa appeal to a PT-symmetric diffraction pattern to interpret their interesting diffraction patterns. In addition to the use of symmetry that does not permit a chiral signature, calculated patterns impose cylindrical symmetry on Tb sites with no justification. We review magnetic symmetries for TbB4 consistent with a published neutron powder diffraction pattern and susceptibility measurements. On the basis of this information, noncollinear antiferromagnetic order exists below a temperature ≈44 K with no ferromagnetic component. Our symmetry-informed patterns encapsulate Tb electronic degrees of freedom in terms of multipoles consistent with established sum rules for dichroic signals. The investigated symmetry templates are noncentrosymmetric, noncollinear antiferromagnetic constructions with propagation vector k=(0,0,0). An inferred chiral signature for a parity-even absorption event has an interesting composition. There is the anticipated product of Tb axial dipoles and chargelike quadrupoles (from Templeton-Templeton scattering). Beyond this contribution, though, symmetry allows a product of dipoles in the chiral signature. A predicted change in the intensity of a Bragg spot with rotation of the crystal about the reflection vector (an azimuthal angle scan) can be tested in future experiments. Likewise contributions to Bragg diffraction patterns from Tb anapoles and higher-order Dirac multipoles. Published by the American Physical Society 2024

Crystal structure of AlFe0.95.

Three B2-type inter-metallic AlFe1 - δ phases (0.18 < δ < 0.05) in the Al-Fe binary system were synthesized by smelting and high temperature sinter-ing methods. The exact crystal structure for δ = 0.05 was refined by single-crystal X-ray diffraction. The amount of vacancy defects at the Fe atom sites was obtained by refining the corresponding site occupancy factor, converging to the chemical formula AlFe0.95, with a structure identical to that of ideal AlFe models inferred from powder X-ray or neutron diffraction patterns.

Deuterium Content and Site Occupancy in Iron Sulfide at High Pressure and Temperature Determined Using In Situ Neutron Diffraction Measurements

AbstractWe have performed in situ time‐of‐flight neutron diffraction experiments to examine the uptake of deuterium in iron monosulfide at pressures up to 11.4 GPa and temperatures to 1300 K. A D2 fluid was formed in the experiments through the decomposition of ND3BD3, resulting in an oxygen fugacity of approximately 1.2 log units below the iron‐wüstite buffer. Deuterium positions and site occupancies were determined in FeS V, using Rietveld refinements of the powder neutron diffraction patterns. Our structural model indicates that two normally unoccupied sites in the P63/mmc FeS V structure, at Wyckoff positions 6h and 4f, are partially occupied by D atoms, with the latter being more dominant. The deuterium content Dx in FeSDX increases with both pressure and temperature over the experimental conditions explored, from 0.126 (14) at 2.3 GPa and 787 K to 1.20 (16) at 9.7 GPa and 1300 K. The unit‐cell volume expansion per deuterium atom is 1.53 ± 0.16 Å3 at 6.9 GPa and 960 K, which is smaller than that determined for metallic iron phases at similar conditions. The variation in unit‐cell volume indicates that most deuterium is lost from FeS V upon temperature quenching at high‐pressures. By fitting the obtained FeS V deuterium site occupancies to a thermodynamic model, estimates for the hydrogen contents of iron monosulfide at conditions and oxygen fugacities consistent with the base of the cratonic lithosphere can be made. This results in values in the range of 1,700–2,700 ppm, which contribute to approximately 2–3 ppm hydrogen in the bulk mantle.

Structure Determination and Analysis of the Ceramic Material La0.987Ti1.627Nb3.307O13 by Synchrotron and Neutron Powder Diffraction and DFT Calculations

In this paper, the ternary system La2O3-TiO2-Nb2O5 is studied to find new ternary phases with useful electrical properties. The solid solution La3−xTi5−3xNb10−2xO39.5−12.5x was recently identified, and this study focuses on the structural characterization of this solid solution with x = 0.04. The crystal structure, representing a new structural type, was determined from synchrotron and neutron powder diffraction data. The unit cell parameters are a = 7.332 Å, b = 7.421 Å, c = 10.673 Å, α = 84.15°, ß = 80.16°, γ = 60.37°, and space group P1¯. The titanium and niobium atoms are disordered in five different crystallographic sites coordinated octahedrally by oxygen atoms. The eight-coordinated La atoms are embedded in the octahedral framework. Ti and Nb preferentially occupy different sites, and this feature was studied using periodic density functional theory methods. Energies of possible Ti/Nb distributions were calculated and the results agree well with the site occupancies obtained by combined Rietveld refinement of synchrotron and neutron powder diffraction patterns. The geometries optimized by DFT also agree well with the structural parameters determined by diffraction. The general agreement between the theoretical calculations and the experimental data justifies the quantum chemical methods as reliable complementary tools for the structural investigation of ceramic materials.

Relationship between magnetoresistance behavior and magnetic states in intercalated compounds FexTiS2

Temperature and field-dependent neutron powder diffraction (NPD) measurements have been performed to reveal the nature of the unusual evolution of the magnetoresistance behavior with increasing Fe content in the intercalated compounds ${\mathrm{Fe}}_{x}{\mathrm{TiS}}_{2}$ (with $x=0.25,0.33,0.50,0.55$) synthesized by solid-phase reaction method with prolonged homogenization heat treatment. As derived from neutron diffraction measurements, both the ${\mathrm{Fe}}_{0.25}{\mathrm{TiS}}_{2}$ and the ${\mathrm{Fe}}_{0.50}{\mathrm{TiS}}_{2}$ compound exhibit an antiferromagnetic (AFM) order below their respective N\'eel temperatures ${T}_{N}\ensuremath{\approx}52$ K and ${T}_{N}\ensuremath{\approx}140\phantom{\rule{4pt}{0ex}}\mathrm{K}$, which results in the presence of a large magnetoresistance accompanying the field-induced phase transition from AFM to the ferromagnetic (FM) state. At low temperatures, this AFM-FM transition is irreversible, confirmed by the irreversibility of changes in the NPD patterns and the presence of remnant magnetoresistance. In contrast, ${\mathrm{Fe}}_{0.33}{\mathrm{TiS}}_{2}$ shows short-range magnetic order at ${T}_{f}\ensuremath{\approx}44$ K due to a triangular network of intercalated Fe atoms and frustrations of exchange interactions with a field-induced FM alignment of Fe magnetic moments in an applied magnetic field as revealed by NPD measurements. The field-induced transformations of the cluster glass magnetic state in this compound lead to a significant decrease in electrical resistivity. According to NPD data, a reduced impact of an external magnetic field on the electrical resistivity of the compound ${\mathrm{Fe}}_{0.55}{\mathrm{TiS}}_{2}$ can be ascribed to the presence of ferromagnetic or ferrimagnetic order in compounds with the Fe concentrations above $x=0.50$. The results obtained indicate that the distribution of the Fe atoms, along with their concentration in ${\mathrm{Fe}}_{x}{\mathrm{TiS}}_{2}$ layered compounds, plays a decisive role in the formation of the magnetic state and the behavior of the magnetoresistance.

Direct Observation of Size-Dependent Phase Transition in Methylammonium Lead Bromide Perovskite Microcrystals and Nanocrystals.

Methylammonium (MA) lead halide perovskites have been widely studied as active materials for advanced optoelectronics. As crystalline semiconductor materials, their properties are strongly affected by their crystal structure. Depending on their applications, the size of MA lead halide perovskite crystals varies by several orders of magnitude. The particle size can lead to different structural phase transitions and optoelectronic properties. Herein, we investigate the size effect for phase transition of MA lead bromide (MAPbBr3) by comparing the temperature-dependent neutron powder diffraction patterns of microcrystals and nanocrystals. The orthorhombic-to-tetragonal phase transition occurs in MAPbBr3 microcrystals within the temperature range from 100 to 310 K. However, the phase transition is absent in nanocrystals in this temperature range. In this work, we offer a persuasive and direct evidence of the relationship between the particle size and the phase transition in perovskite crystals.

Unusually High Magnetic Moments Reported for the High-Spin Co2+ Ions at Axially Elongated CoO4X2 (X = Cl, Br, S, Se) Octahedral Sites: Overestimated Magnetic Moments Caused by Underestimated Magnetic Form Factors

An irreconcilable discrepancy between theory and experiment concerning the magnetic moments of the high-spin Co2+ (d7, S = 3/2) ions at the axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedral sites was pointed out in our recent study [ Inorg. Chem. 2020, 59, 18319−18324]. The magnetic moments μobs of the Co2+ ions in materials containing the CoO4X2 units, determined from refinements of powder neutron diffraction patterns collected in their magnetically ordered states, were found to be notably larger than the spin-only moment of 3 μB (namely, 3.22–4.45 μB). Characteristically, the moments increase almost linearly with the bond-length ratio R = rCo–X/rCo–O, despite the fact that the orbital moments of the Co2+ ions are essentially quenched according to theoretical analyses and DFT + U + SOC computations. In this work, we probe the probable cause for the overestimation of magnetic moments in the ordered magnetic structures. We argue that the overestimated magnetic moments of the Co2+ ions and their increase with the bond-length ratio R originate from the underestimated magnetic form factors of the Co2+ ions at the CoO4X2 octahedral sites. The magnetic form factor F(q) of the Co2+ ion in each CoO4X2 octahedron is the Fourier transform of the magnetic moment distribution ρ(r) around the Co2+ ion, which is the electron density distribution associated with the magnetic orbitals (i.e., the singly occupied d-states) of the CoO4X2 octahedron. The conventional implementation of the magnetic form factor in refinement codes employed an approximation with a q-dependence calculated from the atomic wave function of the isolated ion. Since the spin moment distribution of ρ(r) at the axially elongated CoO4X2 (X = Cl, Br, S, Se) octahedral sites is delocalized from the Co2+ sites to its surrounding ligands, the moment distribution becomes anisotropic in shape. Use of the truncated and spherical approximation underestimates the form factor of the Co2+ ion, and its use in neutron diffraction refinements overestimates the magnetic moments. This effect becomes more pronounced as the moment density distribution is more delocalized along the Co–X direction.

Neutron scattering study of the Tm2Ir2O7 pyrochlore iridate

The newly synthesized ${\mathrm{Tm}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ iridate is investigated using neutron scattering techniques. Powder neutron diffraction patterns confirm that ${\mathrm{Tm}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ crystallizes in a cubic structure of pyrochlore type, consistent with the rest of the rare-earth ${A}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ series, and the crystal structure is preserved down to 0.2 K. The thermal expansion of the crystal lattice is well described by a Debye model of lattice vibrations. A weak magnetic signal consistent with the so-called all-in-all-out magnetic order (AIAO) is traced at low temperature; however, it cannot serve as unambiguous evidence of the AIAO structure in the compound. Nondispersive magnetic excitations in energy-momentum space are observed in inelastic neutron scattering spectra of ${\mathrm{Tm}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$. The crystal-field scheme and parameters of the thulium iridate are refined and discussed with respect to the specific heat and magnetization data. The results are supported by mean-field calculations.

Effect of Bi substitution on the cationic vacancy ordering in SrMoO4-based complex oxides: Structure and properties

The electronic and crystal structures of the Sr1−3xBi2xФxMoO4 series (0.025 ≤ x ≤ 0.30, where Ф represents cation vacancies) were studied. The 0.025 ≤ x ≤ 0.15 compositions showed a defect scheelite structure. Powder X-ray and neutron diffraction patterns for compositions with 0.15 < x ≤ 0.225 exhibited a tetragonal supercell with asup ≈ √5a, csup ≈ c where a and c are the tetragonal scheelite cell parameters. Strong distortion of MoO4 polyhedra was shown by Raman spectroscopy and described by the calculated phonon spectra of “virtual crystals” of Bi2+[MoO4] and Ф2+[MoO4]. The electronic structures were calculated for both types of structure. The decrease of the calculated energy gap is consistent with experimental data from Kubelka-Munk measurements. The electroconductive properties were measured by A.C. impedance spectroscopy. For Sr1−3xBi2xФxMoO4 compositions conductivity increases with increasing x-value, with maximum values of conductivity at 948 K of 2.82 × 10−5S cm−1 for the x = 0.20 composition.

Neutron diffraction study and temperature variation of magnetic anisotropy in Bi substituted nickel ferrite

Bismuth doped NiFe2O4 (NFO) polycrystalline samples: Ni1-xBixFe2O4 with x = 0.00, 0.05 and 0.10, were synthesized using solid-state reaction method. The crystal structural, magnetic structure and magnetic properties of parent NFO and Bi-doped NFO samples were characterized using X-ray diffraction (XRD), neutron powder diffraction (NPD) and magnetization (M) versus magnetic field (H) isotherms, respectively. Rietveld refinement of XRD and NPD patterns confirms the formation of a single-phase cubic spinel crystal structure. No observable change in the lattice parameter was found (within the error limits) with the 5 at % Bi doping to NFO, whereas ≈0.15% change in the lattice parameter was observed in case of 10 at % Bi-doped NFO. Room temperature magnetic structure studies using NPD reveal a net magnetic moment of 1.55(3) μB/f. u., in the case of NiFe2O4. The net magnetic moment at room temperature changes to 1.61(4) μB/f.u. and 1.47(5) μB/f.u. for Ni0.95Bi0.05Fe2O4 and Ni0.90Bi0.10Fe2O4, respectively. The same observation was also inferred from the spontaneous magnetization (Msp) obtained from approach-to-saturation (ATS) analysis of M-H isotherms. Temperature (T) dependence of Msp follows a T2 decline. Approximately 14% increase in magnetic anisotropy was observed in Ni0.95Bi0.05Fe2O4 compared to NiFe2O4 in the temperature range 5 K -300 K.

Nonmonotonic Magnetic Field Dependence of Remnant Ferroelectric Polarization in Reduced Graphene Oxide–BiFeO3 Nanocomposite

The thin‐film heterostructures or nanocomposites exhibit vastly different properties from those observed in bulk systems. Herein, in a nanocomposite of reduced graphene oxide (RGO) and BiFeO3 (BFO), the remnant ferroelectric polarization is found to follow nonmonotonic magnetic field dependence at room temperature as the applied magnetic field is swept across 0–20 kOe on a pristine sample. Bulk BiFeO3, in contrast, exhibits monotonic suppression of polarization under magnetic field. The remanent ferroelectric polarization, in the present case, is determined, primarily, from powder neutron diffraction patterns recorded under 0–20 kOe field. The nanosized (≈20 nm) particles of BFO are anchored onto the graphene sheets of RGO via FeC bonds with concomitant rise in covalency in the FeO bonds. Field‐dependent competition between positive and negative magnetoelectric coupling arising from magnetostriction due to, respectively, interface and bulk magnetization appears to have given rise to the observed nonmonotonic field dependence of polarization. The emergence of FeC bonds and consequent change in the magnetic and electronic structure of the interface region have influenced coupling between ferroelectric and magnetic properties remarkably and thus creates a new way of tuning the magnetoelectric properties via reconstruction of interfaces in nanocomposites or heterostructures of graphene/single‐phase‐multiferroic systems.

Structural and Magnetic Properties of Nanosized Half-Doped Rare-Earth Ho0.5Ca0.5MnO3 Manganite

We investigated the structural and magnetic properties of 20 nm-sized nanoparticles of the half-doped manganite Ho0.5Ca0.5MnO3 prepared by sol-gel approach. Neutron powder diffraction patterns show Pbnm orthorhombic symmetry for 10 K &lt; T &lt; 290 K, with lattice parameters a, b, and c in the relationship c/√2 &lt; a &lt; b, indicating a cooperative Jahn–Teller effect, i.e., orbital ordering OO, from below room temperature. In contrast with the bulk samples, in the interval 250 &lt; T &lt; 300 K, the fingerprint of charge ordering (CO) does not manifest itself in the temperature dependence of lattice parameters. However, there are signs of CO in the temperature dependence of magnetization. Accordingly, below 100 K superlattice magnetic Bragg reflections arise, which are consistent with an antiferromagnetic phase strictly related to the bulk Mn ordering of a charge exchange-type (CE-type), but characterized by an increased fraction of ferromagnetic couplings between manganese species themselves. Our results show that in this narrow band half-doped manganite, size reduction only modifies the balance between the Anderson superexchange and Zener double exchange interactions, without destabilizing an overall very robust antiferromagnetic state.

Homogeneous-like Alkyne Selective Hydrogenation Catalyzed by Cationic Nickel Confined in Zeolite

The selective hydrogenation of alkynes to their corresponding alkenes is an important type of organic transformation, which is currently accomplished by modified palladium catalysts. Herein, we rep...

Average and local structure analysis of Na/Li ion-exchanged Lix(Mn,Ni,Ti)O2 using synchrotron X-ray and neutron sources

Mn-rich layered Lix(Mn,Ni,Ti)O2 was synthesized by Na/Li ion exchange of a P3-Na0.7(Mn,Ni,Ti)O2 precursor. The combined chemical analysis with the ICP-AES, titration technique, and XANES indicated that their electroneutralities were satisfied in some vacancies of the transition metals (TMs). Average structure analyzed using synchrotron X-ray and neutron powder diffraction patterns confirmed a significant amount of vacancies at TM sites and further revealed the existence of a minor tetrahedral Li in the layered rock-salt type Lix(Mn,Ni,Ti)O2. Electrochemical properties of Li0.6Na0.02Mn0.71Ni0.13Ti0.12□0.04O2 exhibited high first discharge capacity of ca. 250 mAh g−1 and high cyclability of exceeding 200 mAh g−1 at the 50th cycle. PDF analysis achieved good fittings for the both total scatterings of synchrotron X-ray and neutron with additional tetrahedral Li and some TM vacancies. Each (Mn,Ni,Co)O6 octahedron in the refined local structure was calculated and expressed as 3D distributions, where the NiO6 and the host MnO6 octahedra were visually characterized as significantly less distorted and highly distorted octahedra, respectively. The co-substitution of Ni2+ ant Ti4+ played the role of stabilizing whole structure and preserving the transition metal vacancy to maintain the high capacity during cycles.

Structural resolution and mechanistic insight into hydrogen adsorption in flexible ZIF-7.

Flexible metal–organic frameworks offer a route towards high useable hydrogen storage capacities with minimal swings in pressure and temperature via step-shaped adsorption and desorption profiles. Yet, the understanding of hydrogen-induced flexibility in candidate storage materials remains incomplete. Here, we investigate the hydrogen storage properties of a quintessential flexible metal–organic framework, ZIF-7. We use high-pressure isothermal hydrogen adsorption measurements to identify the pressure–temperature conditions of the hydrogen-induced structural transition in ZIF-7. The material displays narrow hysteresis and has a shallow adsorption slope between 100 K and 125 K. To gain mechanistic insight into the cause of the phase transition correlating with stepped adsorption and desorption, we conduct powder neutron diffraction measurements of the D2 gas-dosed structures at conditions across the phase change. Rietveld refinements of the powder neutron diffraction patterns yield the structures of activated ZIF-7 and of the gas-dosed material in the dense and open phases. The structure of the activated phase of ZIF-7 is corroborated by the structure of the activated phase of the Cd congener, CdIF-13, which we report here for the first time based on single crystal X-ray diffraction measurements. Subsequent Rietveld refinements of the powder patterns for the gas-dosed structure reveal that the primary D2 adsorption sites in the dense phase form D2–arene interactions between adjacent ligands in a sandwich-like adsorption motif. These sites are prevalent in both the dense and the open structure for ZIF-7, and we hypothesize that they play an important role in templating the structure of the open phase. We discuss the implications of our findings for future approaches to rationally tune step-shaped adsorption in ZIF-7, its congeners, and flexible porous adsorbents in general. Lastly, important to the application of flexible frameworks, we show that pelletization of ZIF-7 produces minimal variation in performance.

Local Structure Investigation of Core-Shell CoFe2O4@γ-Fe2O3 Nanoparticles

We investigate the local structure of nanoparticles based on cobalt ferrite core with and without a hydrothermal surface treatment of variable duration of time that promotes a coating shell by crossing information obtained from atomic absorption spectroscopy (AAS), X-ray powder diffraction (XRD), neutron powder diffraction (NPD), and X-ray absorption spectroscopy (XAS) measurements. Chemical titration results show that the surface layer thickness increases as the duration of the surface treatment increases. The cation distribution obtained by Rietveld refinement of NPD patterns allows splitting the core and shell structural parameters obtained from Rietveld refinement of XRD data of the samples well described in a core-shell model. We follow the local structural evolution with the surface treatment time analyzing both XANES and EXAFS regions of the absorption spectrum. As a result, we observe that the surface treatment is not energetically strong enough to provoke changes on the mean oxidation states of the cations in the spinel structure; indeed, the interatomic distances are similar to those found in bulk materials and the inversion degree remains the same after the surface treatment, in good accordance with the cation distribution obtained by Rietveld refinement of NPD data.

Exploring Lithium Doping in the Layered Transition-Metal Oxides As Cathode Materials for Sodium-Ion Batteries

Layered transition metal oxides have been one of the most promising cathode materials in the lithium-ion as well as sodium-ion batteries. In the case of sodium-ion battery configuration, several transition metals elements are electrochemically active, leading to an extensive study on the composition and structure-property relationships. Particularly, substituting elements in the layered structure is one of the effective approaches to alter the composition, structure, and electrochemical properties. The substituted element could be positioned at either transition metal site or alkali site of the layered structure and plays different role depending on the position. In this talk, I will present the substitution of lithium on different sites within the layered oxides and its effect on the electrochemical performances. Lithium was substituted at (1) alkali site of O3-type layered structure and (2) transition metal site of P2-type layered structure as cathode materials for sodium-ion batteries. The substitution sites were identified by synchrotron and neutron powder diffraction patterns. Each type was compared with transition metal oxides that do not include lithium in order to understand the role of lithium in each substitution site.

(Invited) Cation-Disordered Li3VO4-Based Materials As a Pseudocapacitive Negative Electrode

The growing demand for fast charge-discharge electrical energy storage (EES) devices with long cycles lifetimes has led to the need for alternatives to current battery systems, which store energy via slow faradic reactions. Among different EES technologies, electric double layer capacitors (EDLCs) are considered as promising devices due to their high-power, safe and long-lived characteristics. One of the approaches to further enhance the cell voltage and energy density of EDLCs while maintaining their high power is to replace the activated carbon with ultrafast lithium ion battery materials as hybrid supercapacitors.The orthorhombic β-Li3VO4 (β-LVO) has been identified as a promising negative electrode material for hybrid supercapacitors, with theoretical specific capacity of 394 mAh g-1 (2 lithium accommodation)[1]. The electron-donor effect of Li, exactly opposite to the inductive effect of polyanions, lowers the redox potentials of V5+/V4+ and V4+/V3+ to a safe but still low potential range between 1.3 and 0.4 V vs. Li/Li+, compared to the 3.0 V usually observed for V2O5. Recent our studies [1-2] unveiled that both the structure and electrochemical signature change of the β-LVO during the initial cycling, resulting in what we termed as electrochemical activation process. This electrochemical activation process induces the transformation of β-LVO from the pristine cation-ordered structure into an activated LVO, which has a Li+/V5+ cation-disordered structure. Charge discharge curves also change from “battery-like” plateau to “pseudocapacitive” slope via such cation-disordering of LVO, along with its reaction mechanism change from two-phase to solid-solution reaction[2]. Li+ diffusion coefficient (DLi ) evaluation by galvanostatic intermittent titration technique (GITT) reveals that the DLi of cation-disordered LVO is two orders of magnitude higher than the one of pristine β-LVO. Yet, the preparation method of cation-disordered LVO has been a major issue as the electrochemical activation process of β-LVO is impractical from the industrial point of view. Such electrochemical process requires a precycling of β-LVO for 10-20 cycles down to low potential below 0.4 V vs. Li/Li+, which is difficult to control and inevitably produces undesirable irreversible capacity for a full cell assembling.In this talk, we introduce an alternative to the electrochemical process, i.e., the direct synthesis of fully cation-disordered LVO via simple mechanical milling of the pristine β-LVO powder (Fig.1). The mechanochemical process brings about the disordering of LVO cation sublattice and thus enables to obtain thermodynamically metastable cation-disordered LVO phase without any precycling. Comparison of X-ray and neutron powder diffraction patterns confirmed the successful direct synthesis of cation-disordered LVO. The mechanochemically cation-disordered LVO shows superior rate performances to those of β-LVO and even electrochemically cation-disordered LVO. Another strategy to synthesize pseudocapacitive LVO-based material is a partial substitution of V5+ with Si4+ in β-LVO, which results in a transformation into γ-Li3+xV1-xSixO4. The γ-Li3+xV1-xSixO4 , with a partially V5+/Si4+ cation-disordered structure shows similar psuedocapacitive behavior as a fully cation-disordered LVO with enhanced DLi and rate capability compared to the β-LVO, thanks to the randomly distribution of V5+. In the presentation, we introduce those two approaches, “fully” or “partially” cation-disordering, as new paths for transformation of battery into pseudocapacitive materials with improved electrochemical performances by simple cation mixing.

A Nonlinear Optical Switchable Sulfate of Ultrawide Bandgap

Nonlinear optical (NLO) switchable materials have attracted intense attention because of their promising applications in optoelectronic devices. However, previous studies are mainly limited to mole...

Structural, photocatalytic and electroconductive properties of bismuth-substituted CaMoO4

The Ca1−3xBi2xФxMoO4 system (0.025 ​≤ ​x ​≤ ​0.30, where Ф represents cation vacancies) was synthesized and studied. The 0.025 ​= ​x ​≤ ​0.15 compositions show a tetragonal defect scheelite structure. Powder X-ray and neutron diffraction patterns for compositions with 0.15 ​< ​x ​≤ ​0.225 exhibit a tetragonal supercell with asup ​≈ ​√5a, csup ​≈ ​c where a and c are the tetragonal scheelite cell parameters. Transmission electron microscopy shows that Ca0.4Bi0.4MoO4, crystals consist of three crystallographic domains: (1) defect scheelite; (2) tetragonal superlattice and (3) incommensurately modulated. Photocatalytic properties were studied using Rhodamine B water solutions under UV light. Catalytic activity increases with increasing Bi content. The conductivity of 0.15 ​< ​x ​≤ ​0.225 compositions is 10−7 to 10−8 ​S ​cm−1 in the range 500–650 ​°C, while compositions in the range 0.025 ​= ​x ​≤ ​0.15 show conductivity values from 10−3 to 10−8 ​S ​cm−1 from 500 to 800 ​°C.