A-sites Research Articles

Formation process of halogen-rich argyrodite: elemental disordering of atomic arrangement at the 4a and 4d sites in a heat treatment

Formation process of halogen-rich argyrodite: elemental disordering of atomic arrangement at the 4a and 4d sites in a heat treatment

Site-selective cobalt substitution in La–Co co-substituted magnetoplumbite-type ferrites: 59Co-NMR and DFT calculation study

The La–Co co-substituted magnetoplumbite-type (M-type) ferrites AFe12O19 (A = Ca, Sr and Ba, ion sizes Ca2+ < Sr2+ < Ba2+) with Co compositions around 0.2 have been subjected to 59Co-NMR. The results show that Co occupies the 4f1, 2a and 12k sites, and that the smaller the A ion, the more Co tends to occupy the 4f1 minority spin site, which is effective in enhancing both uniaxial anisotropy and magnetisation. First-principles total energy calculations based on density functional theory (DFT) of undoped AFe12O19 and a supercell ( 2×2×1 of the unit cell) in which 1/96 of Fe3+ is replaced by Co2+ were performed to predict the stable structure and Co occupancy sites. The results show that regardless of A, Co is most stable when it occupies the 4f1 site, followed by the 2a and 12k sites with energy differences on the order of 100 meV, and Co practically does not occupy the 2b and 4f2 sites. As the A ion becomes smaller, the energy difference when Co occupies each Fe site tends to increase, and the Co occupancy of the 4f1 site also increases. The site selectivity of Co can be roughly explained as a result of the difference in uniaxial strain along the c-axis associated with the difference in A. However, the influence of the A ion differs between the R and S blocks and the local strain also has a secondary effect on the Co distribution. Based on these results, the guidelines for improving the performance (anisotropy and magnetisation) of La–Co co-substituted M-type ferrite magnets with a limited amount of Co can be summarised as follows: It is effective to select as small A ions as possible and to post-anneal at low temperature or cool slowly to concentrate Co at the 4f1 site in tetrahedral coordination.

Mg/Ta dual-site doping of high-nickel layered cathode material LiNi0.9Co0.1O2 for extended cycling and thermal stability

Due to its high specific capacity and low cost, high-nickel layered oxide LiNi0.9Co0.1O2 has found promising application as the cathode materials for lithium-ion batteries. However, the crystallographic instability induced by Li+/Ni2+ anti-site exchange, the interfacial parasitic reactions and the microcracking caused by internal stress jointly contribute to the mechano-chemical failure of LiNi0.9Co0.1O2, leading to its fast capacity decay and high thermal stability concern. In this regard, a Mg/Ta dual-site doping strategy was proposed for LiNi0.9Co0.1O2, for which Mg2+ was doped in situ during the synthesis of cathode precursor, while Ta5+ ions were incorporated after the precursor synthesis. This novel synthesis approach leads to unique dual-site occupations of Mg2+ and Ta5+ in the 3a and 3b crystallographic sites respectively. The Mg2+ ions residing in 3a site can function as pillar ions by preventing the Li+/Ni2+ anti-site exchange and inhibiting layered to rock-salt phase transition. The Ta5+ ions occupying 3b site not only leads to the expanded lithium layer spacing but also creates interfacial protection and well-ordered microstructure in LiNi0.9Co0.1O2. Consequently, the dual-site-doped LiNi0.9Co0.1O2 outperforms the pristine and single-site-doped samples. For instance, its full cell shows a greatly enhanced cycling stability from 57.3 % to 90.5 % after 300 cycles at 1C/1C and well improved thermal stability from 205.2 °C to 225.6 °C, compared to the pristine sample. This Mg/Ta dual-site doping strategy provides a facile and practical way to improve the electrochemical and thermal performances of high-nickel layered cathode material LiNi0.9Co0.1O2.

Water‐facilitated targeted repair of degraded cathodes for sustainable lithium‐ion batteries

AbstractDirectly repairing end‐of‐life lithium‐ion battery cathodes poses significant challenges due to the diverse compositions of the wastes. Here, we propose a water‐facilitated targeted repair strategy applicable to various end‐of‐life batches and cathodes. The process involves initiating structural repair and reconstructing particle morphology in degraded LiMn2O4 (LMO) through an additional thermal drive post‐ambient water remanganization, achieving elemental repair. Compared to solid‐phase repair, the resulting LMO material exhibits superior electrochemical and kinetic characteristics. The theoretical analysis highlights the impact of Mn defects on the structural stability and electron transfer rate of degraded materials. The propensity of Mn ions to diffuse within the Mn layer, specifically occupying the Mn 16d site instead of the Li 8a site, theoretically supports the feasibility of ambient water remanganization. Moreover, this method proves effective in the relithiation of degraded layered cathode materials, yielding single crystals. By combining low energy consumption, environmental friendliness, and recyclability, our study proposes a sustainable approach to utilizing spent batteries. This strategy holds the potential to enable the industrial direct repair of deteriorated cathode materials.

Investigating the preferential sites of Co2+ substitution in SrCoxFe12−xO19 using Mössbauer spectroscopy

In this paper, a series of M-type hexagonal SrCoxFe[Formula: see text]O[Formula: see text] ([Formula: see text], 0.25, 0.5) samples have been prepared by sol–gel method. X-ray diffraction (XRD) showed that the samples produced were all p63/mmc space groups of single hexagonal crystals, and the lattice parameters a, b and c did not show the expected trend with increasing x. This was related to the valence changes and lattice distortion caused by the substitution of Co[Formula: see text] at the 2a and 4f2 sites. Room temperature Mössbauer spectra studies showed that when [Formula: see text], Fe[Formula: see text] ions were not uniformly distributed, preferring the 4f1, 4f2 and 2a sites; when [Formula: see text], Co[Formula: see text] ions preferentially displaced the 2a and 4f2 sites and the presence of Fe[Formula: see text] was detected; when [Formula: see text], Co[Formula: see text] ions preferentially displaced the 4f1 and 2b sites and the percentage of Fe[Formula: see text] occupancy was reduced, with a greater occupancy ([Formula: see text] occurring at the 12k site, indicating a preference of Fe[Formula: see text] of the doped sample for this site. This work will provide an important reference for the variation of properties induced by different ion doping substitutions of the Fe sites in the hexagonal ferrite family.

Heflikite, ideally Ca2(Al2Sc)(Si2O7)(SiO4)O(OH), the first scandium epidote-supergroup mineral from Jordanów Śląski, Lower Silesia, Poland and from Heftetjern, Tørdal, Norway

Abstract Heflikite, the first Sc-dominant epidote-supergroup mineral, was discovered in two occurrences. The holotype was found in a granitic pegmatite associated with rodingite-like calc-silicate rocks and metasomatised granitic bodies exposed in a serpentinite quarry at Jordanów Śląski near Sobótka, Lower Silesia, SW Poland. The cotype comes from the Heftetjern pegmatite, Tørdal region, Norway. The holotype is composed of (in wt.%): 35.69 SiO2, 0.22 TiO2, 21.98 Al2O3, 6.12 Sc2O3, 0.07 V2O3, 1.10 Fe2O3, 0.11 Y2O3, 1.55 La2O3, 4.05 Ce2O3, 0.31 Pr2O3, 1.53 Nd2O3, 0.40 Sm2O3, 0.11 EuO, 0.56 Gd2O3, 0.14 MnO, 3.56 FeO, 0.16 MgO, 19.16 CaO and 1.78 H2O(+)calc.; total 98.60. The cotype contains: 34.92 SiO2, 0.44 TiO2, 0.82 SnO2, 19.13 Al2O3, 4.79 Sc2O3, 1.96 Fe2O3, 2.55 La2O3, 7.39 Ce2O3, 0.48 Pr2O3, 0.67 Nd2O3, 0.12 EuO, 0.61 Gd2O3, 0.13 MnO, 5.97 FeO, 17.66 CaO and 1.73 H2O(+)calc.; total 99.37. The compositions correspond to the following empirical formulae: (Ca1.729Ce0.125La0.048Nd0.046Gd0.016Sm0.012Pr0.010Y0.005Eu2+0.003)Σ1.994[(Al2.182Sc0.449Fe3+0.070V3+0.005)Σ2.706(Fe2+0.251Mg0.020Mn0.010)Σ0.281Ti0.014]Σ3.001(Si3.006O11)O(OH) and (Ca1.644Ce0.235La0.082Nd0.021Gd0.018Pr0.015Eu2+0.004)Σ1.019[(Al1.958Sc0.362Fe3+0.128)Σ2.448(Fe2+0.434Mn0.009)Σ0.443(Ti0.029Sn0.029)Σ0.058]Σ2.949(Si3.033O11)O(OH), respectively, and to the ideal formula Ca2(Al2Sc)(Si2O7)(SiO4)O(OH). The crystal structure of the holotype was refined in the monoclinic system with an R1 index of 8.62%. The crystal-structure refinement indicates exclusively Si occupied T sites, Al occupied M1 and M2 sites, and a Ca occupied A1 site. The M3 site is filled predominantly by trivalent cations, mainly Sc3+, with divalent cations (mainly Fe2+) as minor occupants. The A2 site is filled mostly by Ca with minor amounts of rare earth elements (REE). The holotype heflikite crystallised from metasomatic fluids that infiltrated a contact between the granitic pegmatite and the surrounding rodingite-type calc-silicate rocks and serpentinites. The fluids that introduced Sc into the pegmatite could have been either hydrothermal or related to low-grade regional metamorphism that postdated the formation of the pegmatite. The cotype heflikite formed during the late-stage hydrothermal crystallisation of the Sc-enriched granitic pegmatite.

Tartrate-gel synthesized BaFe12-xCuxO19 (0 ≤ x ≤ 1) nanoceramics: Magnetic and catalytic properties

Magnetic catalysts present distinct advantages over their non-magnetic counterparts, primarily due to their ease of recovery from the reaction mixture through magnetic separation. Herein, magnetic and catalytic properties of Cu-substituted barium hexaferrite (BaFe12-xCuxO19, 0 ≤ x ≤ 1) nanoceramics, synthesized via a tartrate-gel method, are evaluated. Using XRD, FTIR, Raman, SEM, XPS, and VSM techniques, the synthesized compositions were characterized. The powder XRD analysis revealed that all samples predominantly consisted of hexaferrite phase, with small impurity phases, α-Fe2O3, CuO and BaFe2O4. The structural parameters (a, b, c), extracted from Rietveld refinement analysis, increased with ‘x’, primarily due to substitution of smaller Fe3+ cation by larger Cu2+ cation. The FTIR and Raman spectra of the samples exhibited characteristic bands corresponding to the M-type hexaferrite. A red-shift occurred in these bands as the Cu amount increased in the Ba-hexaferrite lattice, owing to increase in metal-oxygen bond length. Due to sintering aid nature of copper, considerable increase in the particle size is observed with inclusion of Cu. XPS spectral analysis indicated the oxygen defects in the Cu-substituted sample. The magnetic parameters (MS, HC, and K1) are found to decrease upon incorporation of Cu ions into the Ba-hexaferrite crystal structure. Conversely, the Curie temperature (TC) showed a slight increase with Cu content ‘x’. The unsubstituted sample (x = 0) exhibited no catalytic activity in the reduction of nitrophenol, whereas both Cu-substituted samples displayed enhanced activity with comparable rate constants (0.02 min−1). This activity was attributed to the presence of Cu ions at the octahedral sites (2a or 4f2). Additionally, a magnetic separation process followed by a reusability test was conducted for the x = 0.5 sample over five successive cycles. The consistent activity observed in each cycle underscored the robustness of the engineered magnetic catalyst.

Synthesis, crystal structure and hydrogenation properties of MgxLi3-xB48-y (x = 1.11, y = 0.40).

The ternary magnesium/lithium boride, MgxLi3-xB48-y (x = 1.11, y = 0.40, idealized formula MgLi2B48), crystallizes as its own structure type in P43212, which is closely related to the structural family comprising α-AlB12, Be0.7Al1.1B22 and tetra-gonal β-boron. The asymmetric unit of title structure contains two statistical mixtures Mg/Li in Wyckoff sites 8b with relative occupancies Mg:Li = 0.495 (9):0.505 (9) and 4a with Mg:Li = 0.097 (8):0.903 (8). The boron atoms occupy 23 8b sites and two 4a sites. One of the latter sites has a partial occupancy factor of 0.61 (2). Both unique Mg/Li atoms adopt a twelvefold coordination environment in the form of truncated tetra-hedra (Laves polyhedra). These polyhedra are connected by triangular faces to four [B12] icosa-hedra. The boron atoms exhibit four kinds of polyhedra, namely penta-gonal pyramid (coordination number CN = 6), distorted tetra-gonal pyramid (CN = 5), bicapped hexa-gon (CN = 8) and gyrobifastigium (CN = 8). At the gas hydrogenation of MgLi2B48 alloy, formation of the eutectic composite hydride LiBH4+Mg(BH4)2 and amorphous boron is observed. In the temperature range 543-623 K, the hydride eutectics decompose, forming MgH2, LiH, MgB4, B and H2.

The effect of cation size on structure and properties of Ba-based tetragonal tungsten bronzes Ba4M2Nb10O30 (M = Na, K or Rb) and Ba4M2Nb8Ti2O30 (M = Ca or Sr).

The second largest family of oxide ferroelectrics, after perovskites, are the tetragonal tungsten bronzes (TTB) with the general formula A24A12C4B12B28O30. Cation disorder in TTBs is known to occur if the size difference between cations is small, but the impact of cation disorder on structure and properties has not yet been extensively addressed. In this study we investigate the effect of the size of the M cation, including cation disorder, on the crystal structure and dielectric properties in the two series Ba4M2Nb10O30 (BMN, A = Na, K and Rb) and Ba4M2Nb8Ti2O30 (BMNT, M = Ca, Sr). Dense and phase pure ceramics in the two series were prepared by a two-step solid state synthesis route. The crystal structures of the materials were characterized by powder X-ray diffraction combined with Rietveld refinement. A close to linear relation between the in-plane lattice parameter (a) and the size of the M-cation were observed. Ba4M2Nb8Ti2O30 was shown to possess cation disorder on the A-sites in line with previous work on Ba4M2Nb10O30. Thermodynamic calculations from density functional theory also indicated a drive for cation disorder in the three BMN compositions. Non-ambient temperature X-ray diffraction revealed contraction of the in-plane (a) and expansion of the out-of-plane (c) lattice parameters at the ferroelectric phase transition for Ba4M2Nb10O30. The ferroelectric transition temperature acquired by dielectric spectroscopy showed a systematically increasing TC with decreasing size of the M-cation within both compositional series studied. The compositional dependence of TC is discussed with respect to the size of the M-cation, cation disorder and the tetragonality, as well as the Ti-content. The relaxor to ferroelectric properties observed by polarization-electric field hysteresis loops are discussed in relation to the relative size of cations on the on A1 and A2 sites and the Ti-content.

Cage compound Sc5Pt24B12: a Pt-stuffed variant of filled skutterudite structure. Electronic and structural properties.

The title compound was obtained from elements via arc melting and its crystal structure was determined from single-crystal X-ray diffraction data (space group Im3̄, a = 10.2042(6) Å). The refinement indicated the occupancy of icosahedral 2a and cubooctahedral 8c sites solely by Sc atoms which leads to the composition Sc5Pt24B12 in contrast to the previously reported ternary stannides of Gd3Ni8Sn16 type (RE5-xM12Sn24(+x) compounds). The compound is the first representative of borides crystallizing with a site exchange variant of this stannide structure type. The structural relationships of the boride structure and filled skutterudite LaFe4P12vs. the Remeika phase of Yb3Rh4Sn13-type are discussed. Analysis of chemical bonding classifies Sc5Pt24B12 as a cage compound exhibiting the ionic interaction of cationic scandium species in the cages of anionic framework, formed by covalently bonded B and Pt atoms. Electronic structure calculations show that the electronic states of atoms centered around the cubooctahedral 8c site, i.e. Sc2 3d-, Pt2 5d- and B 2p-states dominate the density of states (DOS) at the Fermi level EF. Strong effect of spin-orbit coupling on the band structure at the gamma point has been found from density functional theory calculations. Sc5Pt24B12 exhibits superconductivity with a transition temperature of TC = 2.45 K.

Microstructure parameter-dependent non-collinear magnetic structures in scandium-doped M-type hexaferrite nanocrystals.

The quest for materials with non-collinear magnetic structures has been driven by their unique properties and potential applications in advanced spintronics and data storage technologies. In this study, we investigate the induction of a non-collinear conical state in BaFe12O19 (M-type) nanocrystal fibers through the substitution of Fe3+ ions with diamagnetic Sc3+ ions. This substitution introduces an additional parameter for tuning the magnetic structure and allows precise control over the substitution amount. We demonstrate that the non-collinear conical state remains stable within a temperature range of 125 K to 325 K and can be finely adjusted by varying the Sc3+ substitution amount. The selective occupancy of Sc3+ ions at the 2a, 4f2, and 2b sites within the M-type ferrite lattice weakens the super-exchange interaction between Fe1, Fe2, and Fe5 ions. This weakening disrupts interactions between different blocks S/R (R*/S*) and stabilizes the conical state. These findings highlight a significant approach to modulating non-collinear magnetic structures in hexagonal ferrites, with implications for both fundamental research and practical applications in the development of novel magnetic materials.

Dielectric and Optical Properties of δ‐Bi2O3 Quaternary Semiconducting Solid Solutions

Quaternary compositions of polycrystalline Bi1.74Dy0.14W0.12−xScxO3 (x = 0.02, 0.03, 0.04, 0.05, 0.06) solid solutions are synthesized by the solid‐state reaction method. The 4a site symmetry of the space group occupied by Sc3+ ion retains the cubic fluorite‐type over a wide temperature range (450–700 °C) for low Sc3+ content without losing the δ‐phase. Dielectric and ionic conductivity by complex impedance in the frequency range from 0.1 to 100 kHz suggests a temperature‐ and Sc3+‐dependent relaxation process. The ionic conductivity increases with the Sc3+ content over the whole tested temperature range. An oxygen ion conductivity of 0.102 Scm−1 at 700 °C and an activation energy of 0.32 eV are achieved for x = 0.06. Optical properties and Rietveld refinement indicate a bandgap reduction due to a bond length reduction (Bi—O). These materials have potential in photocatalysis and water‐splitting technology due to their UV and visible region absorption capabilities.

Thermal behaviors during lithium diffusion in Li0.4WO3 bronze studied by elastic and quasi-elastic neutron scattering.

Polycrystalline Li0.4WO3 bronze has been synthesized by solid state reaction carried out in a silica tube at 10-7 MPa and 973 K. The sample is characterized by temperature-dependent neutron elastic and quasielastic scatterings. The room-temperature neutron powder data Rietveld refinement confirmed the space group Im3̄ along with lithium occupancy found predominantly at the 6b crystallographic site. Upon increasing temperature above 300 K lithium at 6b site decreases and at 2a site increases, suggesting Li+ cation diffusion between these two sites demonstrated by quasielastic neutron scattering as well. The lattice thermal expansion anomaly is observed between 380 K and 450 K, which is explained in terms of lithium dynamic disorder (non-equilibrium) as complemented by elastic and quasielastic neutron scatterings. DFT calculations with different lithium distributions at two different crystallographic sites guide to understand the lattice expansion anomaly. The lattice thermal expansion is modeled using Grüneisen first-order approximation, where the Debye-Einstein-Anharmonicity approach provides the temperature-dependent vibrational energy. The DFT-calculated phonon density of states and bulk modulus help extract the characteristic Debye and Einstein frequencies.

Study on the relationship between structure and magnetic properties of τ-phase MnAl prepared by cryo-milling

The unique characteristics, such as high magnetic moment, high Curie temperature, large magnetic crystalline anisotropy, and low cost, make the τ-phase MnAl a promising candidate as the market alternatives which could fill the gap between the rare earth magnets and ferrite magnets. Because at low temperatures the metal will become more brittle, the cryomilling technology may allow the τ-phase MnAl to be broken quickly and introduce few crystal defects, and then obtain better permanent magnetic properties. In this study, the cryomilling technology was used to grind the τ-phase MnAl, and the structural and magnetic properties of the obtained powder sample were investigated. It was found that compared to room-temperature ball milling, the morphology of cryomilled powders is granular and the powder agglomeration is dramatically suppressed at a low temperature, and as a result the larger particles tend to be broken down into smaller ones rather than being agglomerated to larger thin layers. The grain size D reduced continuously from 145 nm to 36 nm when the sample was milled for 120 minutes. The coercivity increased with increasing the cryo-milling time, while the saturation magnetization decreased. The maximum coercivity of up to 4.9 kOe was obtained by cryo-milling for 100 minutes. By the neutron diffraction analysis, it was confirmed that the decrease of the saturation magnetization with increasing milling time is mainly due to the migration of Mn atoms from 1a site to the 1d site and the decrease of Mn atomic magnetic moment.

Novel High-Temperature Modification of Belomarinaite KNaSO4: Crystal Structure and Thermal Order–Disorder Phase Transitions

Belomarinaite KNaSO4 (space group P3m1, a = 5.6072(3), c = 7.1781(4) Å and Z = 2) has been studied by high-temperature single crystal X-ray diffraction. The K and Na atoms are disordered, and M1(1c) and M2(1b) sites merge into an M1(2d)(K50%/Na50%) site with increasing temperature, and novel translationsgleiche phase transition of belomarinaite KNaSO4 (P3m1 → P-3m1) was revealed at 123 °C. Then, the temperature increase leads to phase transition of P3¯m1-polymorph of KNaSO4 to α-KNaSO4 (P63/mmc) at 446 °C, and sodium and potassium atoms in K1(1a) and Na1(1b) sites merged into an M4(2a)(K50%/Na50%) site. Crystal structures of KNaSO4 were refined at 300, 500 and 750 °C to R1 = 0.057, 0.056 and 0.048, respectively. The BVS maps and bond-valence energy landscape (BVEL) have been calculated, and the probability of the Na+ migration has been predicted using structural data for belomarinaite at 25 °C. The Na+ ion migration can occur at 2.14 eV in the ab plane and 2.80 eV along the c axis at 25 °C.

Investigation of Stable Structures and Electronic States of Spinel MgCo2−ZNi0.5MnAlzO4 (z = 0, 0.3) during Discharge Process As Cathode Materials for Magnesium Rechargeable Batteries Using First-Principles Calculations

Introduction Recently, it is focused on storage batteries materials for reduce of greenhouse gases. In particular, the development of large equipment like as electric vehicles is driving demand for storage battery materials. Although lithium-ion batteries are currently used as storage battery devices, Li metal is a rare metal and expensive, and the development of higher capacity battery materials is needed. Our research group is focusing on magnesium secondary battery cathode materials. In previous report, spinel MgCo2-xMnxO4 (x=0~0.5) (space group Fd-3m) has synthesized and evaluated its battery characteristics, showing an initial discharge capacity of more than 200mAh/g when the Mn substitution amount is x=0.5.1) Since the inclusion of substituted species improves battery properties, we synthesized Al substituted spinel MgCo2-zNi0.5MnAlzO4. In this study, we reported that Mg/Co cation mixing, which was particularly problematic at z=0.3 was reduced compared to MgCo2-xMnxO4 resulting in improved cycle properties.2) The purpose of this study is to clarify the stable local structure of pristine and discharge process of spinel type MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) and to determine the contribution of Al substitution to the electronic structure by performing electron density calculation. Calculation The structural relaxation calculation was performed by generalized gradient approximation (GGA) exchange-correlation potential used with a plane-wave cutoff energy of 550 eV, and 1×2×2 k-point mesh was applied, corresponding to the inverses of the lattice constants on Vienna Ab-initio Simulation Package (VASP) code. The convergence criterion for structural optimization was that the energy difference per iteration be less than or equal to 0.02 eV/Å. 2×1×1 supercell was created and structural relaxation calculation was performed on various initial structural models to determine the energetically optimal structure. Initial structure models were constructed to ensure reproduction of the occupancies determined by an average structure analysis from Rietveld analysis using synchrotron X-ray diffraction. Result and discussion In this study, we performed structural relaxation calculations for spinel-type MgCo2-zNi0.5MnAlzO4 (z=0, 0.3) to obtain the stable structure before and during charge-discharge. The initial model before charging and discharging was created based on the occupancy of each site obtained by crystal structure analysis using neutron diffraction measurements.2) The initial model at discharge was obtained by inserting Mg into the 16c vacancy site in the stable structure before charging and discharging. Figure 1 shows the stable structure after structural relaxation calculations before for a-1) z=0 and b-1) z=0.3 and after discharge (y=0.375) for a-2) z=0 and b-2) z=0.3, respectively. The solid circled Mg is the inserted one, and the dotted circle is the 8a site that became vacant after the structural relaxation calculation in Fig. 1. The crystal structure in pristine was spinel structure, however, it is found that the 4-coordinated 8a site became a vacancy and Mg occupied the 16c site, changing the crystal structure to a rocksalt structure after discharge. Since the 8a and 16c site are close to each other, the insertion of Mg into the 16c site causes a structural change due to the repulsion between atoms and cations on the 8a site, which leads to a chain transfer to other vacancy 16c sites. In particular, models with large structural changes tended to have stable structures. It is also found that Mg remained at the 8a site in z=0.3 shown in b-2) than in z=0 shown in a-2), and that Co at the 8a site could not move to the vacancy in z=0, and that the amount of change in the entire structure is less than that in z=0.3. As a result of partial density of states (PDOS) calculation, it is confirmed that Co and Mn had 2.6 ~ 2 valence and Mn is considerably close to 3 valence during discharge. It is also found that the PDOS of Ni did not almost change before and after discharging, and that no valence change occurred. These results are consistent with those of previously reported XANES measurements.2) Therefore, the model in Fig. 1 determined in this study is considered to be valid. Acknowledgement This research was financially supported by JST, ALCA-SPRING Grant Number JPMJAC1301, Japan. This work was also supported in part by JSPS KAKENHI Grant Number 20K15382, Japan. Dr. Koji Ohara of JASRI (Japan Synchrotron Radiation Research Institute for assistance with synchrotron X-ray total scattering measurements (BL04B2, SPring-8, Proposal Nos. 2019B1249).1) Y. Idemoto, M. Ichiyama et al., J. Power Sources, 482 , 228920 1-9 (2021)2) Y. Hirata, Y. Idemoto et al., ECS Meeting s, MA2020-02 , 3451 (2020) Figure 1

First-Principles Calculations on Diffusion and Association Behavior of Fluoride Ions in Ba-Doped LaF3 Solid Electrolyte

Fluoride ion batteries, which generate electrical energy through the fluorination/de-fluorination reaction of electrode active materials, are expected to be the next-generation storage batteries with high energy density. LaF3 with a tysonite-type structure is known as one of the representative solid-state fluoride ion conductors. Substitutional solid solution of divalent cations such as Ba or Sr ions at La sites forms fluoride ion vacancies as charge compensation, resulting in fluoride ion conductivity. The main objective of this study is to analyze the formation behavior of point defects in LaF3 through quantitative evaluation of their formation energies using first-principles calculations, and to elucidate the conduction mechanism of fluoride ions in LaF3.The plane-wave basis PAW method implemented in VASP code was used for the electronic structure calculations. The electron correlation treatment uses the PBEsol-type potential based on the generalized gradient approximation. Calculations for given point defects were performed. The cutoff energy of the plane wave basis sets was set to 420 eV, and the structure optimization calculations were performed until the Hellmann-Feynman force acting on each atom was less than 0.02 eV/Å.There are three fluoride ion sites (12g, 4d, and 2a) in the unit cell of LaF3. Using the supercell model, we calculated the defect formation energies of fluoride ion vacancies at each site. The formation energies at the 12g, 4d, and 2a sites are 0.17 eV, 0.52 eV, and 0.52 eV, respectively. According to the defect formation energies, fluoride ion vacancies are most likely to form at the 12g sites.To elucidate the elementary processes of fluoride ion transfer between 12g sites by the vacancy mechanism, we performed first-principles calculations and transition state search using the Nudged Elastic Band method. From symmetry, four different pathways exist in the lattice of undoped LaF3. The pathway with the highest energy barrier is shown to have very low transfer energies, 0.17 eV, and the energy barriers of the other pathways are less than 0.1 eV. These results suggest that LaF3 has a potential for very fast fluoride ionic conductivity by the vacancy mechanism. In the presentation, the mechanism of fluoride ion conduction in Ba-doped LaF3 will also be reported. This work was supported by the RISING2 (JPNP16001) and the RISING3 (JPNP21006) projects from the New Energy and Industrial Technology Development Organization (NEDO), Japan.

Antisite-Defects Control of Magnetic Properties in MnSb2Te4.

The intrinsic magnetic topological materials Mn(Sb/Bi)2n+2Te3n+4 have attracted extensive attention due to their topological quantum properties. Although, the Mn-Sb/Bi antisite defects have been frequently reported to exert significant influences on both magnetism and band topology, their formation mechanism and the methods to manipulate their distribution and concentration remain elusive. Here, we present MnSb2Te4 as a typical example and demonstrate that Mn-Sb antisite defects and magnetism can be tuned by controlling the crystal growth conditions. The cooling rate is identified as the primary key parameter. Magnetization and chemical analysis demonstrate that a slower cooling rate would lead to a higher Mn concentration, a higher magnetic transition temperature, and a higher saturation moment. Further analysis indicates that the Mn content at the original Mn site (MnMn, 3a site) varies more significantly with the cooling rate than the Mn content at the Sb site (MnSb, 6c site). Based on experimental observations, magnetic phase diagrams regarding MnMn and MnSb concentrations are constructed. With the assistance of first-principles calculations, it is demonstrated that the Mn-Sb mixing states primarily result from the mixing entropy and the growth kinetics. The present findings offer valuable insights into defects engineering for preparation of two-dimensional quantum materials.

Crystal chemistry of type paulkerrite and establishment of the paulkerrite group nomenclature

Abstract. A single-crystal structure determination and refinement has been conducted for the type specimen of paulkerrite. The structure analysis showed that the mineral has monoclinic symmetry, space group P21/c, not orthorhombic, Pbca, as originally reported. The unit-cell parameters are a=10.569(2), b=20.590(4), c=12.413(2) Å, and β=90.33(3)∘. The results from the structure refinement were combined with electron microprobe analyses to establish the empirical structural formula A1[(H2O)0.98K0.02]Σ1.00 A2K1.00 M1(Mg1.02Mn0.982+)Σ2.00 M2(Fe1.203+Ti0.544+Al0.24Mg0.02)Σ2.00 M3(Ti0.744+ Fe0.263+)Σ1.00 (PO4)4.02 X[O1.21F0.47(OH)0.32]Σ2.00(H2O)10 ⋅ 3.95H2O, which leads to the end-member formula (H2O)KMg2Fe2Ti(PO4)4(OF)(H2O)10 ⋅ 4H2O. A proposal for a paulkerrite group, comprising orthorhombic members benyacarite, mantiennéite, pleysteinite, and hochleitnerite and monoclinic members paulkerrite and rewitzerite, has been approved by the International Mineralogical Association's Commission for New Minerals, Nomenclature and Classification. The general formulae are A2M12M22M3(PO4)4X2(H2O)10 ⋅ 4H2O and A1A2M12M22M3(PO4)4X2(H2O)10 ⋅ 4H2O for orthorhombic and monoclinic species, respectively, where A= K, H2O, □ (= vacancy); M1 = Mn2+, Mg, Fe2+, Zn (rarely Fe3+); M2 and M3 = Fe3+, Al, Ti4+ (and very rarely Mg); X= O, OH, F. In monoclinic species, K and H2O show an ordering at the A1 and A2 sites, whereas O, (OH), and F show a disordering over the two non-equivalent X1 and X2 sites, which were hence merged as X2 in the general formula. In both monoclinic and orthorhombic species, a high degree of mixing of Fe3+, Al, and Ti occurs at the M2 and M3 sites of paulkerrite group members, making it difficult to get unambiguous end-member formulae from the structural determination of the constituents at individual sites. To deal with this problem an approach has been used that involves merging the compositions at the M2 and M3 sites and applying the site-total-charge method. The merged-site approach allows end-member formulae to be obtained directly from the chemical analysis without the need to conduct crystal-structure refinements to obtain the individual site species.

Crystal Growth and the Structure of a New Quaternary Adamantine Cu□GaGeS4

Single crystals of quaternary adamantine-type Cu□GaGeS4 were grown using the chemical vapor transport technique, with iodine as the transport agent. Dark red transparent crystals were grown in a temperature gradient of DT = 900–750 °C. Chemical characterization by X-ray fluorescence showed the off-stoichiometric composition of Cu□GaGeS4 crystals—in particular, a slight Ge deficiency was observed. By X-ray diffraction, Cu□GaGeS4 was found to adopt the chalcopyrite-type structure with the space group . Cation distribution in this structure was analyzed by multiple energy anomalous synchrotron X-ray diffraction, and it was found that Cu and vacancies occupied the 4a site, whereas Ga and Ge occupied the 4b site. The band gap energies of several off-stoichiometric Cu□GaGeS4 crystals were determined by UV-Vis spectroscopy and ranged from 2.1 to 2.4 eV. A non-linear correlation of the band gap energy with the Ge content of the compound was shown to follow the usual bowing behavior of semiconductor alloys, with a bowing parameter of = −1.45 (0.08).