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Co-containing fluoride-phosphates are of interest in sense of delivering high electrode potentials and attractive specific energy values as positive electrode materials for rechargeable batteries. In this paper we report on a new Co-based fluoride-phosphate, LiNaCoPO4F, with a layered structure (2D), which was Rietveld-refined based on X-ray powder diffraction data [P2(1)/c, a = 6.83881(4) angstrom, b = 11.23323(5) angstrom, c = 5.07654(2) angstrom, beta = 90.3517(5) degrees, V = 389.982(3) angstrom(3)] and validated by electron diffraction and high-resolution scanning transmission electron microscopy. The differential scanning calorimetry measurements revealed that 2D-LiNaCoPO4F forms in a narrow temperature range of 520-530 degrees C and irreversibly converts to the known 3D-LiNaCoPO4F modification (Pnma) above 530 degrees C. The non-carbon-coated 2D-LiNaCoPO4F shows reversible electrochemical activity in Li-ion cell in the potential range of 3.0-4.9 V vs. Li/Li+ with an average potential of approximate to 4.5 V and in Na-ion cell in the range of 3.0-4.5 V vs. Na/Na+ exhibiting a plateau profile centered around 4.2 V, in agreement with the calculated potentials by density functional theory. The energy barriers for both Li+ and Na+ migration in 2D-LiNaCoPO4F amount to 0.15 eV along the [001] direction rendering 2D-LiNaCoPO4F as a viable electrode material for high-power Li- and Na-ion rechargeable batteries. The discovery and stabilization of the 2D-LiNaCoPO4F polymorph indicates that temperature influence on the synthesis of A(2)MPO(4)F fluoride-phosphates needs more careful examination with perspective to unveil new structures.

The Li1.17Ni0.17Mn0.50Co0.17O2 Li-rich NMC positive electrode (cathode) for lithium-ion batteries has been coated with nanocrystals of the LiMn1.5Co0.5O4 high-voltage spinel cathode material. The coating was applied through a single-source precursor approach by a deposition of the molecular precursor LiMn1.5Co0.5(thd)5 (thd = 2,2,6,6-tetramethyl-3,5-heptanedionate) dissolved in diethyl ether, followed by thermal decomposition at 400 &deg, C inair resulting in a chemically homogeneous cubic spinel. The structure and chemical composition of the coatings, deposited on the model SiO2 spheres and Li-rich NMC crystallites, were analyzed using powder X-ray diffraction, electron diffraction, high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and energy-dispersive X-ray (EDX) mapping. The coated material containing 12 wt.% of spinel demonstrates a significantly improved first cycle Coulombic efficiency of 92% with a high first cycle discharge capacity of 290 mAhg&minus, 1. The coating also improves the capacity and voltage retention monitored over 25 galvanostatic charge&ndash, discharge cycles, although a complete suppression of the capacity and voltage fade is not achieved.

Vital need to reduce battery cost inspired intensive research in the field of sodium-storage systems, which required extending the range of perspective electrode materials. Herein, we present a new member of the electrochemically active NASICON material family, rhombohedral NaMo2(PO4)3, which demonstrates both Mo+4/Mo+5 and Mo+4/Mo+3 redox activities towards sodium (de)intercalation. Desodiation of the initial NaMo2(PO4)3 material with subsequent discharge within the 1.2–4.0 V range leads to a multi-electron redox transition with reversible capacity of 130 mAh g−1. However, the single Mo+4/Mo+3 redox transition at 2.45 V (vs. Na/Na+) with capacity of 95 mAh g−1 was found to be more stable during cycling, and operando X-ray diffraction confirmed its two-phase mechanism. Sodiation of the initial phase results in Na2.5Mo2(PO4)3, which maintains the parent NASICON structure (R-3c, a = 8.90532(7) A, c = 22.2379(3) A, V = 1527.30(3) A3), with two Na-positions being almost equal in occupancy and energy.

The carbon-coated single-phase samples of the pyrophosphates AMoP2O7 (A = Li and Na) were synthesized using freeze-drying followed by annealing in a sealed silica tube with the Fe/FeO getter. The Rietveld refinement of the X-Ray powder diffraction data proved both structures are built up as a network of corner-linked MoO6 octahedra and P2O7 groups with A-cations located in the open tunnels running along the [100] (LiMoP2O7) and [101] (NaMoP2O7) directions. The bond valence energy landscapes (BVEL) analysis revealed three-dimensional pathways of alkali-ion migration with significantly different activation energies (0.8 eV for LiMoP2O7 and 4.5 eV for NaMoP2O7) anticipating LiMoP2O7 to exhibit faster Li+ diffusion and better electrochemical characteristics. Both materials displayed electrochemical activity in Li- and Na-cells with reversible capacities of ∼20 mA h g−1 for NaMoP2O7 and more than 70 mA h g−1 for LiMoP2O7, being in a good agreement with the BVEL results.

In this work, we present a combined approach comprising of crystallochemical methods such as Voronoi-Dirichlet partition (VDP), bond valence sums mapping (BVSM) and bond valence energy landscapes (BVEL) for the search for Na-ion cathode materials. Using this approach a systematic screening of the inorganic crystal structure database (ICSD-2016/2) was performed to extract potential cathode materials for Na-ion batteries. As a result, a down-selected and reviewed list of known and newly discovered cathode materials compared and characterized structurally with a special focus on Na + mobility properties revealed by crystallochemical methods is given. DFT calculations were also carried out for a number of materials to validate the screening algorithm, applicability and reliability of the crystallochemical approaches as well as to get a deeper insight on the Na + diffusion properties.

In this paper, we report on a novel RbVPO4F fluoride phosphate, which adopts the KTiOPO4 (KTP) type structure and complements the AVPO4F (A = alkali metal) family of positive electrode (cathode) materials for metal-ion batteries. RbVPO4F was synthesized via a freeze-drying assisted solid-state route and characterized via structural, computational and electrochemical methods. RbVPO4F represents the first example of reversible electrochemical Rb+ de/insertion in a crystalline oxypolyanionic framework. The electrochemical measurements on RbVPO4F in a three-electrode cell configuration in RbClO4-saturated propylene carbonate (PC) electrolyte revealed that the material exhibits reversible Rb+ de/insertion within the 0.4–1.3 V vs. Ag+/Ag potential range (∼3.9–4.8 V vs. K+/K) displaying rather high diffusion coefficients of (0.3–1.0) × 10−11 cm2 s−1 comparable to those of K+ in KVPO4F that supports reasonably fast ionic mobility in the KTP structure despite the large ionic radius of the Rb+ ions. The energy barriers of Rb+ ion transport are exceptionally low not exceeding 0.2 eV along the c-axis and correlating well with diffusion coefficients estimated using the DFT+U-NEB methodology and with the experimentally determined transport properties. These results suggest a new paradigm for the development of materials that support many monovalent ion reversible de/insertion processes in a single prototypical structural oxypolyanionic framework.

Potassium and sodium-ion transfer kinetics were compared for the intercalation reactions into the KVPO4F positive electrode material in acetonitrile- and ethylene carbonate-based electrolytes, which implied the formation of different electrode/electrolyte interface structures. The presence of surface layers was found to result in a significantly more pronounced effect on the ion transfer kinetics for K+ compared with Na+, while the barrier layers in K+ electrolytes were demonstrated to be less resistive. Difficulties associated with the stabilization of the electrode material/potassium electrolyte interface under high operating potentials require the application of higher voltage electrolytes. The kinetic trends in three high voltage electrolytes were compared for the potassium (de)intercalation reaction, and the general obstacles to developing a high-voltage potassium-ion battery were identified.

NASICON-type lithium-vanadium phosphate (Li 3 V 2 (PO 4 ) 3 ) based electrodes capable to provide extremely fast lithium transport properties were studied by a combination of structure, morphology and surface characterization methods: X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), laser diffraction particle size distribution (PSD), as well as electrochemical methods: potentiostatic (PITT) and galvanostatic (GITT) intermittent titration techniques, electrochemical impedance spectroscopy (EIS), and constant current chronopotentiometry. Significant differences in the kinetics of reversible lithium intercalation depending on the lithiation stage were found: lithium diffusion coefficients, found from the PITT, GITT and EIS data, demonstrate an abrupt drop by 2–3 orders of magnitude (from 10 −9 to 10 −12 cm 2 s −1 ) in the 4.3–4.4 V potential range vs Li/Li + , which is attributed to the LiV 2 (PO 4 ) 3 ↔ V 2 (PO 4 ) 3 phase transition. The electrochemical extraction/insertion of two lithium equivalents can occur at ultra-high rates (up to 320C) from/into structurally more accessible Li2 and Li3 sites, while the de/intercalation of the third lithium equivalent from/into the Li1 position is supposedly hindered kinetically. To analyze the electrochemical data, specially developed theoretical models were used, which take into account geometry and phase configuration of the diffusion space, as well as the properties of the phase boundary interfaces. Morphology and size distribution parameters, essential for mathematical processing of the electrochemical data, were obtained by SEM, PSD and BET methods.

In this work, we provide a structural and computational investigation of the Li2CoPO4F high-voltage cathode material by means of neutron powder diffraction (SG Pnma, a = 10.4528(2) A, b = 6.38667(10) A, c = 10.8764(2) A, RF = 0.0145), crystal chemistry approaches (Voronoi–Dirichlet partitioning and bond valence sums mapping), and density functional theory. The material reveals low energy barriers (0.12–0.43 eV) of Li hopping and a possible 3D channel system for Li-ion migration. It is found that only one Li per formula unit can be extracted within the potential stability window of the commercially available electrolytes. The interrelation between dimensionality, topology and energetics of Li-ion diffusion and peculiarities of the Li2CoPO4F crystal structure are discussed in detail.

LiNaCo 0.5 Fe 0.5 PO 4 F fluoride-phosphate was synthesized via conventional solid-state and novel freeze-drying routes. The crystal structure was refined based on neutron powder diffraction (NPD) data and validated by electron diffraction (ED) and high-resolution transmission electron microscopy (HRTEM). The alkali ions are ordered in LiNaCo 0.5 Fe 0.5 PO 4 F and the transition metals jointly occupy the same crystallographic sites. The oxidation state and oxygen coordination environment of the Fe atoms were verified by 57 Fe Mossbauer spectroscopy. Electrochemical tests of the LiNaCo 0.5 Fe 0.5 PO 4 F cathode material demonstrated a reversible activity of the Fe 3+ /Fe 2+ redox couple at the electrode potential near 3.4 V and minor activity of the Co 3+ /Co 2+ redox couple over 5 V vs Li/Li + . The material exhibited the discharge capacity of more than 82% (theo.) regarding Fe 3+ /Fe 2+ in the 2.4÷4.6 V vs Li/Li + potential range.

The incommensurate modulated crystal structure of Bi2.27Sr1.73CuO6 + δ(2201) phase [a= 5.3874 (5),b= 5.3869 (4),c= 24.579 (3) Å; β = 90.01 (1)°,q= 0.2105 (3)a* + 0.538 (4)c*,Z= 4, the (3 + 1)-dimensional monoclinicA2/a(α0γ) group] has been refined withR= 0.041,wR= 0.052 from X-ray single-crystal data including up to third-order satellite reflections. The same structure has also been considered as incommensurate composite witha2= 2.437,b2= 5.387,c2= 24.614, β2= 93.06,q2= 0.4524a2*−0.243c2*and the (3 + 1)-dimensionalA2/m(α0γ)0sgroup for the second component. Both approaches give quite similar results. The structure possesses oxygen disorder in the oxygen-rich region of the BiO layer. An extra O atom is determined in the bridging position shifted ∼ 0.6 Å from BiO towards the SrO layer. Its presence is the cause of the tremendous increase of the bismuthU11atomic displacement parameter in ∼ 20% of the unit cells (t= −0.05–0.15). Vacancies are determined in the oxygen site of the SrO layer, which may result in the oxygen content variation with annealing at different oxygen pressures. The total refined oxygen content 6.18 (1) corresponds to the results of chemical analysis.

For successful development of novel rechargeable batteries, considerable efforts should be devoted to identifying suitable cathode materials that will ensure a proper level of energy output, structural stability, and affordable cost. Among various compounds explored as electrode materials, structural analogues of minerals–natural stable inorganic solids–occupy a prominent place. The largest number of varieties of phosphate minerals occurs in rare metal granite pegmatites, and many of which contain transition metals as essential components. Transition metal phosphates are promising candidates for exploration as cathode materials due to a perfect combination of easily scalable synthesis, moderate-to-high voltage operation, thermal/chemical stability, and environmental safety. However, impurities usually presented in natural objects, and often inappropriate sample morphologies, do not permit the use of minerals as battery electrode materials. Nevertheless, the minerals of different classes, especially phosphates, are considered as prototypes for developing novel materials for battery applications. The crystal chemical peculiarities of the phosphate representatives that are most relevant in this aspect and the electrochemical characteristics of their synthetic analogues are discussed here.

Phase pure KVPO4F is prepared by firing equimolar amounts of VPO4 and KHF2 under Ar (600 °C, 1 h).

Composite electrode materials based on LiFeBO3 are synthesized under different conditions and studied as the cathodic materials for lithiumion batteries. Composites with different degrees of iron oxidation are synthesized by annealing in a closed system with the use of metal-oxide getters. Based on the results of cyclic voltammetry and galvanostatic cycling of samples with different Fe(II) contents, it is concluded that the surface composition is the determining factor for applicability of materials to reversible processes of inter-calation-deintercalation.

The crystal structures of various mixed Li and transition metal fluoride phosphates are reviewed, with a special focus on their applicability as cathode materials for Li-ion batteries., To satisfy the needs of rapidly growing applications, Li-ion batteries require further significant improvements of their key properties: specific energy and power, cyclability, safety and costs. The first generation of cathode materials for Li-ion batteries based on mixed oxides with either spinel or rock-salt derivatives has already been widely commercialized, but the potential to improve the performance of these materials further is almost exhausted. Li and transition metal inorganic compounds containing different polyanions are now considered as the most promising cathode materials for the next generation of Li-ion batteries. Further advances in cathode materials are considered to lie in combining different anions [such as (XO4)n− and F−] in the anion sublattice, which is expected to enhance the specific energy and power of these materials. This review focuses on recent advances related to the new class of cathode materials for Li-ion batteries containing phosphate and fluoride anions. Special attention is given to their crystal structures and the relationships between structure and properties, which are important for their possible practical applications.

In the search for high-energy materials, novel 3D-fluorophosphates, Li2Co1−xFexPO4F and Li2Co1−xMnxPO4F, have been synthesized. X-ray diffraction and scanning electron microscopy have been applied to analyze the structural and morphological features of the prepared materials. Both systems, Li2Co1−xFexPO4F and Li2Co1−xMnxPO4F, exhibited narrow ranges of solid solutions: x ≤ 0.3 and x ≤ 0.1, respectively. The Li2Co0.9Mn0.1PO4F material demonstrated a reversible electrochemical performance with an initial discharge capacity of 75 mA·h·g−1 (current rate of C/5) upon cycling between 2.5 and 5.5 V in 1 M LiBF4/TMS electrolyte. Galvanostatic measurements along with cyclic voltammetry supported a single-phase de/intercalation mechanism in the Li2Co0.9Mn0.1PO4F material.

The title compound is synthesized by solid state reaction of stoichiometric amounts of LiCo0.5Fe0.5PO4 and NaF (1.

Phase pure KVPO4F is prepared by firing equimolar amounts of VPO4 and KHF2 under Ar (600 °C, 1 h).

Electrochemical performance and structural properties of the high-voltage cathode material Li2CoPO4F have been investigated. The cyclic voltammetry and coulometry under potential step mode in the voltage range 3.0–5.1 V vs. Li revealed a structural transformation at potentials above 4.8 V. This transformation occurring upon Li-extraction appears to be irreversible: the subsequent Li-insertion does not result in restoration of the initial structure, but takes place within a new “modified” framework. According to the structure refinement this modification involves the mutual rotations of (CoO4F2) octahedra and (PO4) tetrahedra accompanied by the considerable unit cell expansion which is expected to enhance the Li-transport upon subsequent cycling. The new framework demonstrates a reversible Li-insertion/extraction in a solid-solution regime with stabilized discharge capacity at around 60 mAh g−1.

A new model of lithium-ion transport processes in the LiFePO 4 electrode is proposed. This model takes into account the phase transition LiFePO 4 ↔ FePO 4 accompanying reversible lithium intercalation into the electrode during potential or current steps. The diffusion coefficient of Li + ion and its dependence on the LiFePO 4 /FePO 4 phase ratio have been determined by means of processing of experimental potential and current transients in accordance with the model's equations. The results of galvanostatic and potentiostatic intermittent titration techniques are in good agreement. The value of diffusion coefficient varies within 10 −10 –10 −16 cm 2 s −1 depending on the lithium content in solid solution Li X FePO 4 and Li 1− X FePO 4 ( X 4 /FePO 4 phase ratio.

New niobium-based misfit sulfides [(Ln1/3Sr2/3S)1.5]1.15NbS2 (Ln=Sm, Tb) have been synthesized from a mixture of SrS, Ln2S3, Nb(m), and S in evacuated and sealed silica tubes by annealing at 100 ...

The present paper describes the synthesis, characterization of mixedvalence bismuthates with 3- or 2-dimensional perovskite-like structures and structural criteria that influence superconductivity in these compounds. Single phase samples of Sr1−x K x BiO3 were prepared for the broad range of K-content: 0.25≤x≤0.65. For these bismuthates the symmetry of the structure changes from monoclinic to orthorhombic and finally to tetragonal upon increasing the K-content thus resulting in the decrease of the Bi-O distances and reduction of the network distortions. Superconductivity with maximum T c=12K exists in the narrow range (x≈0.5–0.6) within the stability field of the tetragonal phase (0.33≤x≤0.65), when the 3-dimensional octahedral framework has close to the ideal perovskite structure arrangement. At the same time compositions with close to optimal Bi-valence (x=0.33 and 0.43) do not show any sign of superconductivity, probably, due to structural distortions. The layered type (Ba, K)3Bi2O7 and (Ba, K)2BiO4 bismuthates belonging to the A n+1B n O3n+1 homologous series were investigated. Buckling of the (BiO2) layers in the structure of the n=2 member was revealed. The formation of the n=1 bismuthate was found by Electron Microscopy and X-ray powder diffraction studies. Both types of compounds are considered to be possible candidates for new superconducting materials among bismuthates.

L batteries originally developed for portable devices can now be found in applications as diverse as power tools, electric vehicles, and stationary energy storage. To satisfy the need of current and new applications, Li-ion batteries require further improvement in terms of performance properties (energy and power density, safety, and cost). Transition metal compounds containing different polyanion units (XO4) m− (X = P, S, Si) are considered as the most promising cathode materials for the next generation of Li-ion batteries due to increased redox potential caused by an inductive effect and remarkable electrochemical and thermal stability ascribed to a three-dimensional structure. Further advances in the polyanion cathodes are related to combining (XO4) m− and F− in the anion sublattice, which is expected to enhance the operating voltage due to the higher ionicity of the M−F bond. Indeed, various fluorophosphates (LiVPO4F, Na2FePO4F) and fluorosulphates (LiMSO4F) have been reported to exhibit attractive electrochemical performance. Among fluorophosphates, compounds of the general formula A2MPO4F (A = Na, Li; M = Fe, Mn, Co, Ni) have received particular interest due to their potential to operate on more than one alkali atom per formula unit (f.u.), which would result in higher specific capacity and energy density. The A2MPO4F fluorophosphates crystallize in three different structure types. While the coordination polyhedra of transition metal, MO4F2 octahedra, is the same for all three, the means of their conjugation varies from edge-shared in Li2MPO4F (M = Ni, Co) and corner-shared in Na2MnPO4F to mixed face-shared and corner-shared in Na2FePO4F, resulting in different architectures. The three-dimensional (3D) Na2MnPO4F and the layered Na2FePO4F were shown to operate as positive electrode material in Naand Li-ion cells with reversible capacity of about 120 mAh g−1 (∼0.8 electron per f.u.). Moreover, the capacity improvement up to ∼180 mAhg−1 (∼1.46 electrons per f.u.) was observed for nanostructured Na2FePO4F cycled at elevated temperature. 12 Several groups reported on high voltage electrochemical performance of Li2CoPO4F and Li2NiPO4F. 8,14−16 These fluorophosphates possess a three-dimensional structure and, by analogy with the olivine phase, are expected to demonstrate good stability and reversibility upon cycling. The complete evaluation of these materials is restrained by the absence of commercial high-voltage electrolytes stable above 4.8 V. The exploration of corresponding Feor Mn-based fluorophosphates with lower redox potentials might provide an advantage in the energy and power density over the LiFePO4 cathode materials. So far, these fluorophosphates have not been identified: apparently, the structure framework could not adopt the Fe and Mn ions, which are larger compared to Co and Ni. In our previous paper, we showed that upon the first charge Li2CoPO4F undergoes structural transformation with the large volume expansion (∼5%) demonstrating the framework flexibility. Considering this “structure pliability” we attempted to stabilize Fe-based fluorophosphate by “expanding” the framework through the substitution of Li ions located in the structure voids by larger Na ions; as a result, we succeeded in synthesis of a new NaLiFePO4F phase isostructural to Li2NiPO4F (Figure 1). Upon preparing this communication, we have found a short report by Mizuta et al., where electrochemical properties measured on the multiphase NaLiFePO4F sample were described. 17 Here, we report on the synthesis employed for obtaining the pure NaLiFePO4F phase, its structure determination, and electrochemical activity. We demonstrate that electrochemical replacement of Na by Li in

A new complex oxide Sr 2 ScBiO 6 was synthesized by a solid state reaction in air. The compound is stable up to 1150°C and acquires the desired oxygen stoichiometry at 850°C. The crystal structure was determined using powder X-ray diffraction, electron diffraction, and high-resolution electron microscopy. Sr 2 ScBiO 6 has a perovskite-derived pseudocubic face-centered unit cell ( a =8.1816(3) A) and a rock-salt ordering of Sc 3+ and Bi 5+ over the B positions. Electron microscopy investigation reveals that the real structure is of the La 2 NiRuO 6 type, monoclinic with cell parameters a ≈ b = a per √2≈5.785 A, c =2 a per ≈8.182 A, and P2 1 / n space group. The structure can be described by an a + b − b − system of the BO 6 octahedral tilting. The presence of numerous twin domains is a characteristic feature of this compound.

Synthesis and physical properties of new superconducting bismuthates, K 1− x A x BiO 3 (A=Bi, La, and Ca), are reported. New compounds could only be prepared in a narrow range of composition, restricted by the A-site cation size, with cubic perovskite structure. For the first two systems (A=Bi, La), T c was found to depend strongly on composition and was enhanced upon heterovalent substitution. The data obtained and comparison with known bismuthates show undoubtedly that band filling controlled by dopant concentration is a crucial parameter for variation of T c in this class of materials.

Bi2Sr1.6La0.4CuO6.33 and Bi2Sr1.2La0.8CuO6.46 are fluorinated using XeF2 as a fluorinating agent and studied by X-ray powder diffraction and high-resolution electron microscopy. The highly fluorinated Bi-2201 phase undergoes a structural transformation that is accompanied by the formation of an I-centered tetragonal unit cell, the suppression of the √2ap×√2ap superstructure, the disappearance of the (BiO)2 modulation, and an elongation of the c parameter of about 1.65–1.77 A. The modification of the Bi2O2 block into a Bi2O2−δF2+δ block with filled tetrahedral interstitial positions is responsible for the observed structural changes and eliminates the mismatch between the (BiO) rock salt layers and the perovskite (CuO2) layers. The structure of the fluorinated material is compared with the structures of other intercalated Bi-based cuprates and phases composing Bi2(O,F)4 blocks in the structure.

The time-of-flight (TOF) neutron powder diffractometer Vega, whose wide solid angle enables us to collect intensity data very efficiently, was utilized for the structure refinement of (K 0.87 Bi 0.13 )BiO 3 prepared at high pressure. Partial profile relaxation improved R factors more or less in Rietveld refinements of superconductors and related materials. An integrated software, REMEDY, for whole-pattern fitting combined with a maximum-entropy method was successfully applied to the determination of nuclear densities in HgBa 2 CuO 4+ δ .

The structure of a superconducting oxide (K0.87Bi0.13)BiO3(Tc≈10.2 K) prepared under high pressure was analyzed by time-of-flight neutron powder diffraction. Rietveld refinement showed this compound to be a cubic perovskiteABO3with space groupPm 3 m(No. 221) and lattice parametera=4.23377(3) A. Refinement of occupation factors revealed the absence of oxygen vacancies and the substitution of Bi3+ions for 13% of K+ions at theAsite, presenting evidence for electron doping in this superconductor. Extraordinarily large atomic displacement parameters for theAand O sites are believed to reflect pronounced positional disorder mainly arising from the large difference in size between the K+and Bi3+ions.

The orthorhombic modification of CaPbO3 was synthesized from a mixture of Ca2PbO4 and PbO2 at high temperature and high pressure. Its structure was analyzed by Rietveld analysis of neutron diffraction data on the basis of space group Pbnm. It has a distorted perovskite structure of the GdFeO3 type and a unit cell with dimensions of a = 5.6710 A, b = 5.8875 A, and c = 8.1495 A. The Pb−O bond lengths in each PbO6 octahedron are comparable to each other, whereas the PbO6 octahedron tilts around [110]p and [001]p axes (p: perovskite subcell) by 18.50° and 20.28°, respectively. These tilt angles, which show great structural distortion in CaPbO3 containing the smaller Ca2+ ion, are much larger than corresponding ones in crystal chemically isotypic SrPbO3. The electric resistivity of CaPbO3 at room temperature was as high as 3 × 103 Ω•cm, which is in sharp contrast to low resistivities observed in other perovskite-type oxides BaPbO3 and SrPbO3. The high resistivity of CaPbO3 is explained as gap formation betwee...

New superconducting compound in the K–Bi–O system was obtained under high pressure. Pure perovskite phase can be prepared for K 1− x Bi 1+ x O 3 in the range x =0.0–0.2. Bulk superconductivity with T c of 10.2 K is observed for samples K 1− x Bi 1+ x O 3 with x =0.0–0.1. Transition temperature T c does not change within this interval, though deviation from the range x =0.0–0.1 leads to deterioration of superconducting properties. X-ray diffraction showed that the structure of the superconducting samples is cubic perovskite, which was confirmed by electron diffraction study. After comparing the present results with known bismuth oxide based superconductors we conclude that doping level plays a predominant role in determining the magnitude of T c in these materials.

We have synthesized a new perovskite-type compound with nominal composition CaPbO 3 under about 6 GPa using a cubic-anvil-type apparatus from a mixed powder of high-purity CaO and PbO 2 . The XRD pattern was indexed on the basis of an orthorhombic unit cell with a = 5.667(1)A, b = 5.879(I)A and c = 8,147(2)A. This compound has a distorted perovskite-type structure, while two previously reported types of CaPbO 3 have a fluorite-type structure and an ilmenate-type structure. EDX analysis and the unit cell parameters suggest a deficiency in the Ca site. The electrical resistivity of this compound at room temperature was very high (> 10 5 Ω cm) in contrast to the metallic and semiconducting conductivity of BaPbO 3 and SrPbO 3+ respectively.

NaLiFePO4F is prepared by annealing a stoichiometric mixture of LiFePO4 and NaF (Ar flow, 650—700 °C, 2 h).

Dicopper(II) dilanthanum pentaoxide, La 2 Cu 2 O 5 , has been prepared using a high-pressure technique. Its structure at 296 and 10 K was analyzed by Rietveld refinements using neutron powder diffraction data. The structure of La 2 Cu 2 O 5 comprises CuO 5 square pyramids connected to each other in three dimensions by corner sharing and ten-coordinate La 3+ ions occupying positions next to oxygen vacancies which form tunnels along the c axis.

Two samples of (Pb 0.5 Cu 0.5 )(Sr 0.5 La 0.5 ) 2 CuO 5 + δ with different oxygen contents ( δ = 0.03 and 0.13) showed superconducting transition temperatures somewhat different from each other: 24 K for the fully oxidized sample and 35 K for the deoxidized sample. The structural parameters of these samples were refined by the Rietveld analysis of neutron powder diffraction data to clarify the structure/property relationship in this nonstoichiometric oxide. In the oxidized sample, excess oxygen partially occupies an interstitial site at (0.151, 1 2 , 0) in a (Pb 0.5 Cu 0.5 )O 1 + δ layer, whereas this site proved to be vacant in the deoxidized sample. All the atoms on this layer are displaced from ideal rock-salt-type positions to achieve more favorable bonding environments. The length of a CuO bond on the CuO 2 conduction sheet is decreased from 1.8985 to 1.8915 A upon oxygen removal. This finding provides unambiguous evidence for the idea that the hole concentration on the CuO 2 sheet increases with releasing excess oxygen from the (Pb 0.5 Cu 0.5 )O 1 + δ layer.

Ca2Sr2Cu3GaO9 with a Tc of 73 K was prepared at 1250°C and 6 GPa. Its neutron powder diffraction data were analyzed on the basis of Ima2, Imcm and P21ab space groups. Imcm gave the best approximation to the actual superstructure with a doubled b dimension. Ca2Sr2Cu3GaO9 belongs to a homologous series of oxides (R1−xCax)n−1Sr2CunGaO2n+3 (R: rare-earth metals). In its structure, GaO4 tetrahedra form (GaO33−)∞ chains running parallel with the c-axis. Sr2GaO3 blocks composed of the infinite chains and Sr2+ ions alternate with (Ca)2(CuO2)3 sheets along the a-axis. Two types of the infinite chains with different orientations of GaO4 tetrahedra alternate along the b-axis, which is the reason for the 2b superstructure. The Cu(1)O5 pyramid tilts owing to the tetrahedral coordination of Ga. The intermediate Cu(2)O2 sheet is nearly flat with each Cu(2) atom having four equivalent CuO bonds. Sr2+ and Ca2+ ions are completely ordered on two different sites. Full occupation of Ca2+ ions at an eight-coordinated site, which is obtained only at high pressure, permits adequate hole doping of the CuO2 sheets, where the formal oxidation state of Cu is +2.33.

Wadsley–Roth phase Li x Nb 9 PO 25 has been studied as a potential candidate for anode material of Li-ion batteries. Its crystal structure, which consists of ReO 3 -type blocks of NbO 6 octahedra connected with PO 4 tetrahedra, provides a good stability and performance during Li + insertion/removal. Li-ion chemical diffusion coefficient ( D chem ) in Li x Nb 9 PO 25 was determined by means of potentiostatic intermittent titration technique and electrochemical impedance spectroscopy. Different data treatments (classical Warburg equation or the model of an electrode system with ohmic potential drop and/or slow kinetics of the interfacial Li + ion transfer across the electrode/electrolyte interface) were used for calculation of D chem of the Li ion inside this material; their applicability is discussed in the article. D chem changes with the Li-ion doping degree, x, in Li x Nb 9 PO 25 and has a sharp minimum near the two-phase region at appr. 1.7 V vs. Li + /Li. These values of D chem in Li x Nb 9 PO 25 (∼10 −9 –10 −11 cm 2 s −1 ) were found to be in average noticeably higher than in the widely studied anode material, Li 4 Ti 5 O 12 .

In a hunt for high-energy cathode materials for Li-ion batteries, different families of fluoride-containing materials such as fluoride-phosphates AxMPO4F (A = Li, Na; M = V, Mn, Fe, Co, Ni; x = 1, 2)1,2,3have been extensively examined. Introduced to the lattice fluorine brings about not only an increase in operating voltages due to its highest electronegativity, but also a richer structural variety. In these systems the nature of alkali and transition metals strongly affects the adopting crystal structure, which in turn determines electrochemical properties. Due to a larger ionic radius compared to Li and Na and somewhat different crystal chemistry, K provides ample opportunities in searching and stabilizing new frameworks for reversible ion de/intercalation. Here we report on a novel vanadium-based AVPO4F (A = Li, K) cathode material adopting a KTP-type framework for high power rechargeable batteries with enhanced specific energy and excellent rate capability4. KVPO4F was prepared via freeze-drying assisted solid-state route in two steps. The composition of the material was studied by TEM-EDX, ICP-AES and FTIR spectroscopy. The structure of KVPO4F was refined from powder XRD data [S.G. Pna21, a = 12.8200(3) Å, b = 6.3952(1) Å, c = 10.6115(2)] using the KFeSO4F structure as an initial model5. The refined structure was confirmed with HAADF-STEM imaging and electron diffraction. Vanadium +3 oxidation state was confirmed with EELS. For the electrochemical evaluation the initial KVPO4F material was oxidized by charging up to 4.8 V vs Li/Li+ at C/20 rate and holding at this potential for 5 hours. According to the EDX data, potassium in not completely removed and about 15% remains in the structure giving rise to a K0.15VPO4F formula. The obtained K0.15VPO4F material was tested within the 2.0–4.7 V vs Li/Li+ potential range at different rates from C/5 to 40C showing an uptake of 0.7 Li per formula unit at the average voltage of ~4 V. K0.15VPO4F exhibits a sloping voltage profile indicating a solid-solution-like de/intercalation mechanism. Ex-situ XRD and electron diffraction tomography were applied to examine the crystal structure of the recovered oxidized and lithiated electrode materials. In contrast to the noncentrosymmetric parent KVPO4F phase (Pna21), the crystal structures of both oxidized and lithiated electrode materials possess a centrosymmetric space group (Pnan); however, KTP-type structure is preserved. The difference in the unit cell volume of all three phases is small and does not exceed 2.2%. LixK0.15VPO4F shows remarkable capacity retention at 40C maintaining more than 50% of theoretical (156 mAh/g) or 75% of initial specific capacity (111 mAh/g at C/5). Rapid kinetics of the Li de/intercalation is also evidenced by rate capability measurements (figure 1). Synthesis, structure and electrochemical properties of the obtained cathode material will be discussed in detail. A special focus will be given on structural peculiarities and substitution in the metal sublattice and their effect on the electrochemical performance in a Li anode cell. Figure 1. Rate capability measurements of (K,Li)VPO4F. References Barker, J.; Saidi, M. Y.; Swoyer, J. L. J. Electrochem. Soc. 2003, 150, A1394−A1398. Okada, S.; Ueno, M.; Uebou, Y.; Yamaki, J. J. Power Sources 2005, 146, 565−569. Ellis, B. L.; Makahonouk, W. R. M.; Makimura, Y.; Toghill, K.; Nazar, L. F. Nat. Mater. 2011, 10, 772−779. Fedotov, S. S.; Khasanova, N. R.; Samarin, A. Sh.; Drozhzhin, O. A.; Batuk, D.; Karakulina, O. M.; Hadermann, J.; Abakumov, A. M; Antipov, E. V. Chem. Mater. 2016, DOI: 10.1021/acs.chemmater.5b04065 Recham, N.; Gwenaelle, R.; Sougrati, M. T.; Chotard, J.-N.; Frayret, C.; Mariyappan, S.; Melot, B. C.; Jumas, J.-C.; Tarascon, J.-M. Chem. Mater. 2012, 24, 4363–4370. Figure 1

Today researches in the field of cathode materials for Li-ion batteries are directed towards the development of new materials with high power and energy densities, especially to answer the requirements of large scale applications. In this respect, fluoride-phosphate materials are very attractive as they demonstrate wide structural diversity. Furthermore, they are expected to exploit the advantages of both anion species: the increase in the working potential due to inductive effect of the polyanion group and higher ionicity of the M−F bond, faster kinetics arising from lower affinity of lithium to the F-anion.1 In the search for new cathode materials for Li-ion batteries we have explored the A2MPO4F and AMPO4F (A=Li, Na, K, and M=Co, Mn, Fe, V) fluorophosphates families. The fluoride-phosphate phases were prepared through different synthetic routes depending on the chemistry of transition metal. Combination of X-ray/neutron diffraction and electron microscopy were applied for a thorough structural characterization. It was shown that in these systems the substitution on the alkali metal site leads to the wide range of adopted structures. Thus, in the Li2FePO4F system synthesis of sodium-containing counterpart, NaLiFePO4F, followed by subsequent electrochemical exchange of Na by Li leads to the cathode material with a 3D “stacked” structure.2 In the (Li,Na)2CoPO4F system it provides a new low-temperature polymorph adopting a complex layered structure, in contrast to the high-temperature phase with 3D “stacked” arrangement. The introduction of large potassium into the AMPO4F system gives a raise to a new cathode material with a KTP structure, which exhibits excellent rate capability.3 Reversible electrochemical activity demonstrated by these fluoride-phosphate materials in Li-cell will be discussed. A special attention will be given to the structure peculiarities and their impact on electrochemical properties, which is important for possible practical applications of these materials. The work was partly supported by Russian Science Foundation (grant 16-19-00190), Skoltech Center for Electrochemical Energy Storage and Moscow State University Development Program up to 2020. References Antipov, E. V.; Khasanova, N. R.; Fedotov, S. S. International Union of Crystallography Journal 2015, 2, 85-94 Khasanova N. R., Drozhzhin O. A., Storozhilova D. A., Delmas C., Antipov E. V. Chem. Mater., 2012, 24, 4271–4273 Fedotov, S. S.; Khasanova, N. R.; Samarin, A. Sh.; Drozhzhin, O. A.; Batuk, D.; Karakulina, O. M.; Hadermann, J.; Abakumov, A. M; Antipov, E. V. Chem. Mater. 2016, DOI: 10.1021/acs.chemmater.5b04065

The incommensurately modulated structure of Bi2Sr2Eu1.3Ce0.7Cu2O10.17, with a = 5.4752(4) Å, b = 5.4522(3) Å, c = 17.860(1) Å, Z = 2, was refined by the GJANA program [Gao et al., Acta Cryst. A 49, 141 (1993)] from X-ray powder data in C:C2mb: 111 four-dimensional space group (Rov = 0.064, Rm = 0.041, Rsat = 0.202, Rp = 0.049, Rwp = 0.065). Displacive modulation parameters of all cations and oxygen atoms in the Bi-layer were involved in the refinement. Obtained results including the modulation parameters are in agreement with those found for the similar phase Bi2Sr1.7Nd1.8Ce0.5Cu2O10+δ from single-crystal data [Mironov et al., J. Solid State Chem. 109, 74 (1994)].

A single crystal of Bi 2 Sr 1.7 Nd 1.8 Ce 0.5 Cu 2 O 10+δ (2222 phase) was obtained and its structure refined, including parameters describing the structural modulation (orthorhombic system, four-dimensional space group C:C2mb: 111, a = 5.5000(4) A, b = 5.4846(7) A, c = 17.873 A, Z = 2). The refinement of the average structure gave R = 0.061, while structure refinement including displacive and thermal modulation parameters resulted in R = 0.042 (overall) and R = 0.030 for the main reflections. The amplitudes and directions of modulation are very similar to those in the 2212 phase (1, 2), with displacements ranging up to 0.4 A. The refinement shows extra oxygen to be located in BiO layers, and gives δ = 0.32(8), in reasonable agreement with previously reported values.

The crystal structure of Li2CoPO4F is completely solved from precession electron diffraction data, including the location of the Li atoms.

The crystal structure of the Li2CoPO4F high-voltage cathode for Li ion rechargeable batteries has been completely solved from precession electron diffraction (PED) data, including the location of the Li atoms. The crystal structure consists of infinite chains of CoO4F2 octahedra sharing common edges and linked into a 3D framework by PO4 tetrahedra. The chains and phosphate anions together delimit tunnels filled with the Li atoms. This investigation demonstrates that PED can be successfully applied for obtaining structural information on a variety of Li-containing electrode materials even from single micrometer-sized crystallites.