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Cation migration on electrochemical cycling can significantly influence the performance of li-ion cathode materials. Phases of composition LiFe2–xInxSbO6 (0 < x nnm, consisting of a hexagonally close-packed array of oxide ions, with Fe/In and Sb cations ordered on octahedral sites, and lithium cations located within partially occupied tetrahedral sites. NPD, SXRD, and 57Fe Mössbauer data indicate that on reductive lithium insertion (either chemically or electrochemically), LiFe2SbO6 is converted to Li2Fe2SbO6 accompanied by large-scale cation migration, to form a partially Fe/Li cation-ordered and Fe2+/Fe3+ charge-ordered phase from which lithium cations cannot be easily removed, either chemically or electrochemically. Partial substitution of Fe with In suppresses the degree of cation migration that occurs on lithium insertion such that no structural change is observed when LiFeInSbO6 is converted into Li1.5FeInSbO6, allowing the system to be repeatedly electrochemically cycled between these two compositions. Phases with intermediate levels of In substitution exhibit low levels of Fe migration on Li insertion and electrochemical capacities which evolve on cycling. The mechanism by which the In3+ cations suppress the migration of Fe cations is discussed along with the cycling behavior of the LiFe1.5In0.5SbO6–Li1.75Fe1.5In0.5SbO6.

International audience; The layered oxide LiNi0.6Mn0.2Co0.2O2 is a very attractive positive electrode material, as shown by good reversible capacity, chemical stability, and cyclability upon long-range cycling in Li-ion batteries and, hopefully, in the near future, in all-solid-state batteries. A large panel of synthesis conditions were explored in order to tailor the size of the primary particles for powders showing structures close to the ideal 2D layered structure (i.e., with less than 3.8% Ni2+ ions in the Li+ sites). Materials with primary particle sizes ranging from 170 nm to 2 μm were obtained. Their electrochemical performance in Li-ion batteries and surface reactivity were characterized in different cycling conditions, as a function of the primary particle size. A significant impact on the performance and reactivity was observed, with obviously better reversible capacity and cyclability for the materials with primary particles ranging between 200 and 400 nm. The analysis of the solid electrolyte interphase formed at the interface between the positive electrode and the electrolyte has shown that larger particles had a larger proportion of lithium salt degradation products, induced by the larger amount of Li2CO3 at their surface. It was also shown that the degradation of the lithium salt was favored at higher cycling rate, whereas that of the organic solvents is a little more favored in larger potential windows with a higher cutoff voltage.

International audience; Fe4Nb2O9 and Co4Nb2O9 are antiferromagnetic compounds belonging to the M4M′2O9 series (M = Mn, Fe, Co; M′ = Nb, Ta), whose structure (P[3 with combining macron]c1) derives from the Cr2O3 corundum one. By mixing cobalt and iron in a 1 : 1 ratio, an Fe2Co2Nb2O9 oxide has been synthesized. Its structural, magnetic and electric characterization studies confirm that its unit cell volume (V = 331.19(1) Å3), Néel temperature (TN = 58 K) and dielectric permittivity are intermediate between those of the Fe4Nb2O9 and Co4Nb2O9 end members. The neutron diffraction study evidences an Fe:Co random occupation of the (4d) Wyckoff sites. Its antiferromagnetic structure, refined in the C2/c′ magnetic space group, shows magnetic moments in the planes of the honeycomb (HC) layers of the M4M′2O9 structure, and stacked along c, as for Fe4Nb2O9 and Co4Nb2O9. However, the magnetic field induced magnetization M(H) of Fe2Co2Nb2O9 below TN differs strongly from both end members, exhibiting a sublinear dependence. A similar rounded shape of the electric polarization P(H) curve is evidenced, in marked contrast to the linear M(H) and P(H) behaviours observed below the spin-flop magnetic field for this class of linear magnetoelectric materials. As a result, Fe2Co2Nb2O9 exhibits larger P values and steeper P responses to H at low H than both Fe4Nb2O9 and Co4Nb2O9 end members. This result is explained by a microscopic model based on the Fe and Co mixed occupation. Substitutional disorder locally allows for stronger magnetoelectric couplings and its effect does not cancel on average. This chemical substitution effect opens a new route to enhance the magnetoelectric response of honeycomb antiferromagnets.

This study presents the influence of polymorphism on the magnetic properties of Co5TeO8. This compound with a spinel-like structure [Co2]A[Co3Te]BO8 was synthesized into two polymorphs: one disordered within a cubic Fd3m structure, where Co2+ and Te6+ ions are randomly distributed on the octahedral B sites [the disordered polymorph can also be presented as an inverse spinel of the formula Co(Co1.5Te0.5)O4] and the other ordered with a cubic P4332 structure where Co2+ and Te6+ ions are ordered on the B sites. The macroscopic magnetic measurements showed that both polymorphs present a ferrimagnetic ordering, below ∼40 K, and a second transition is also observed at 27 K for the ordered polymorph. Neutron powder diffraction data between room temperature and 1.7 K showed as well the presence of short-range magnetic ordered clusters, which appears for both polymorphs below 200 K. At lower temperature, these short-range orders are transformed into long-range ferrimagnetic orders. Below TC = 40 K, the colinear ferrimagnetic structure of the disordered polymorph is described with the I41/am'd' space group. The ordered polymorph undergoes an incommensurate ferrimagnetic spiral spin ordering below TC1 = 45 K, followed by a second magnetic phase transition at TC2 = 27 K. This last transition is associated with the emergence of an additional ferrimagnetic component and an abrupt change in the magnitude of the magnetic propagation vector k = [0, 0, γ] from γ = 0.086 at T = 30 K to γ ≈ 0.14 in the range between 27 and 1.7 K. The magnetic symmetry of the ordered polymorph is described with the P43(00γ)0 magnetic superspace group. We evidenced that the ordering of Co2+/Te6+ on the B sites changes all of the Co-Co and Co-O distances and thus all JAB, JAA, and JBB exchange interactions, between the A and B sites, which are able to stabilize the incommensurate spin modulation in the ordered polymorph.

Topochemical reduction of the cation-disordered perovskite oxides LaCo

Superionic lithium argyrodites are attractive as solid electrolytes for all-solid-state-batteries. These materials of composition Li6PS5X (X = Cl, Br, and I) exhibit structural disorder between the X−/S2− positions, with higher disorder realizing better Li+ transport. Further replacement of the sulfide by chloride anions (for the series Li7−xPS6−xClx) has been shown to increase the ionic conductivity. However, the underlying changes to the lithium substructure are still relatively unknown. Here we explore a larger range of nominal halide compositions in this material from x = 0.25 to x = 1.5 and explore the changes with neutron diffraction and impedance spectroscopy. The replacement of S2− by Cl−causes a lowered average charge in the center of the prevalent Li+ “cages”, which in turn causes weaker interactions with Li+ ions. Analysis of neutron diffraction data reveals that the increased Cl− content causes these clustered Li+ “cages” to become more interconnected, thereby increasing Li+ conductivity through the structure. This study explores the understanding of the fundamental structure–transport correlations in the argyrodites, specifically structural changes withinthe Li+ ion substructure upon changing anionic charge distribution.

The crystal structures of three polymorphs of Rb3ScF6 have been determined through a combination of synchrotron, laboratory X-ray, and neutron powder diffraction, electron diffraction, and multinuclear high-field solid-state NMR studies. The room temperature (RT; α) and medium-temperature (β) structures are tetragonal, with space groups I41/a (Z = 80) and I4/m (Z = 10) and lattice parameters a = 20.2561(4) A, c = 36.5160(0) A and a = 14.4093(2) A, c = 9.2015(1) A at RT and 187 °C, respectively. The high-temperature (γ) structure is cubic space group Fm3m (Z = 4) with a = 9.1944(1) A at 250 °C. The temperatures of the phase transitions were measured at 141 and 201 °C. The three α, β, and γ Rb3ScF6 phases are isostructural with the α, β, and δ forms of the potassium cryolite. Detailed structural characterizations were performed by density functional theory as well as NMR. In the case of the β polymorph, the dynamic rotations of the ScF6 octahedra of both Sc crystallographic sites have been detailed.

International audience; Up to now, the possible occurrence of a cationic ordering on the tetrahedral sublattices of stoichiometric double scheelite-type oxides was not settled, with somewhat contradictory X-ray diffraction and optical measurements [Blasse, G. J. Inorg. Nucl. Chem. 1968, 30, 2091]. Using two different synthesis routes, both ordered and disordered forms of fergusonite La2SiMoO8 were prepared. The crystal structure of the ordered form was determined using powder X-ray and neutron diffraction, which clearly evidence a tridimensional ordering between [SiO4] and [MoO4] tetrahedra. The crystal chemistry of ordered double sheelite-type LaIII2(SiIVO4)(MoVIO4) can be seen as an intermediate between those of simple regular scheelite or fergusonite LnIII(NbVO4) and of ordered triple scheelite BiIII3(FeIIIO4)(MoVIO4)2. The structure of the disordered La2SiMoO8 phase was analyzed using powder X-ray diffraction. A few small and larger diffraction peaks or bumps are observed in addition to the sharper peaks of a simple fergusonite cell. DIFFaX and FAULTS programs helped showing that these faint peaks originate from stacking faults between 2D ordered layers. The intermediate 2D–3D nature of SiO4/MoO4 ordering in seemingly disordered compounds might explain the previous discrepancy between optical and X-ray diffraction measurements.

The recent interest in halide-based solid electrolytes Li3MX6 (M = Y, Er, and In; X = Cl, Br, and I) shows these materials to be promising candidates for solid-state battery application, due to the...

Five substituted oxohydroxoferrates K2–x(Fe,M)4O7–y(OH)y (M=Si, Ge, Ti, Mn, Ir) were synthesized in a potassium hydroxide hydroflux with a molar base‐water ratio q(K) of about 0.9. While the hexagonal prisms of K2–x(Fe,Ti)4O7–y(OH)y crystallize in P63/mcm, all other compounds form hexagonal plates with the trigonal space group Purn:x-wiley:14341948:media:ejic202000891:ejic202000891-math-0001 1 m. The crystal structure of the oxohydroxoferrates resembles ß‐alumina. It consists of honeycomb layers urn:x-wiley:14341948:media:ejic202000891:ejic202000891-math-0002 Fe2O6] of edge‐sharing [FeO6] octahedra, where the hexagonal voids are capped by vertex‐sharing [FeO4] tetrahedra pairs. The cavities between the oxoferrate layers host the potassium ions. Depending on M, the substitution affects different iron positions and varies between 5 and 20 %. The magnetic structures of the antiferromagnetic compounds were determined by neutron powder diffraction. The potassium ion conductivity was characterized by electrochemical impedance spectroscopy at room temperature. By storing the oxohydroxoferrates in air or annealing them at 700 °C the ion conductivity was significantly increased, e. g. to 5.0 ⋅ 10−3 S cm−1 for a pressed pellet of the iridium substituted compound.

The Li–Ni–O phase diagram contains a variety of compounds, most of which are electrochemically active in Li-ion batteries. Other than the well-known LiNiO2, here we report a facile solid-state meth...

Fast-ion conductors are critical to the development of solid-state batteries. The effects of mechanochemical synthesis that lead to increased ionic conductivity in an archetypical sodium-ion conductor Na3PS4 are not fully understood. We present here a comprehensive analysis based on diffraction (Bragg, pair distribution function), spectroscopy (impedance, Raman, NMR, INS) and ab-initio simulations aimed at elucidating the synthesis-property relationships in Na3PS4. We consolidate previously reported interpretations about the local structure of ball-milled samples, underlining the sodium disorder and showing that a local tetragonal framework more accurately describes the structure than the originally proposed cubic one. Through variable-pressure impedance spectroscopy measurements, we report for the first time the activation volume for Na+ migration in Na3PS4, which is ~30% higher for the ball-milled samples. Moreover, we show that the effect of ball-milling on increasing the ionic conductivity of Na3PS4 to ~10-4 S/cm can be reproduced by applying external pressure on a sample from conventional high temperature ceramic synthesis. We conclude that the key effects of mechanochemical synthesis on the properties of solid electrolytes can be analyzed and understood in terms of pressure, strain and activation volume.

Combined neutron and X‐ray powder diffraction techniques highlighted the sorption capacity of the acidic L zeolite towards the L‐lysine amino acid. The role of zeolite channels in the stabilization of the lysine absorbed and the effect of water on protein structure are elucidated at atomistic level. The stabilization of the L α‐helical conformation is related to strong H‐bonds between the tail aminogroups of lysine molecules and the Brønsted acid site as well as to complex intermolecular H‐bond system between water molecules, zeolite and amino acid. This finding is relevant in the catalytic synthesis of polypeptide, as well as in industrial biotechnology by qualitatively predicting binding behaviour, The adsorption capacity of the acidic L zeolite towards the L‐lysine was investigated by combining neutron and X‐ray powder diffraction techniques. The stabilization of the L α‐helical conformation is related to strong H−bonds between the tail aminogroups of lysine molecules and the Brønsted acid site as well as to complex intermolecular H‐bond system between water molecules, zeolite and amino acid.

International audience; While powder diffraction methods are routinely utilized to optimize structural models for compounds whose crystal structures are known, the determination of unknown structures is far more challenging. When the unknown structure is large, structure solution can become a virtually intractable problem using standard structure solution methodologies, especially when the space group cannot be unambiguously resolved. One such system is the promising Na-ion battery cathode material Na3V2(PO4)2F3 whose high temperature and room temperature structures were previously solved, but whose more complex low-temperature structure could not be determined. Here, a novel materials genomic approach is demonstrated for the solution of the unknown 100 K structure of Na3V2(PO4)2F3 in which enumeration methods are first used to generate a large number (~3,000) of trial structures based on plausible orderings of Na ions and then automated Rietveld refinements are carried out to optimize each of these trial structures. Based on both the analysis of the ensemble of optimized trial structures and the density functional theory energy minimization of selected trial structures, the 100 K structure of Na3V2(PO4)2F3 is best described as belonging to the space group A21am with unit cell dimensions of a = 9.01928(4), b = 27.1379(1), c = 10.73307(5). The 100 K unit cell has a large volume of 2627.07(2) Å3 with Z = 12 and 33 independent crystallographic sites (9 Na, 3 V, 3 P, 12 O, and 6 F) that is 3x and 6x larger than the room- and high-temperature polymorphs of this phase, respectively. The novel methods described here will be generally applicable for the solution of the complex cation-ordered structures that commonly occur for battery materials.

Elemental substitution in lithium nickel oxide (LiNiO2, LNO) is among the most common strategies employed in search of a commercially viable cathode active material (CAM) with the highest possible energy density at reasonable cost (as offered by Ni-rich CAMs). Here, we revisit Ga substitution of Ni in LNO, for which there is a lack of systematic studies, despite promising electrochemical performances reported in the literature. We demonstrate successful synthesis by wet-mixing, pre-annealing and solid-state reaction of the precursors, as shown by electron microscopy and synchrotron-based X-ray diffraction (XRD). The site occupation of Ga ions in the Li interlayer is suggested (corresponding to Li1−yGayNiO2). Electrochemical testing of the as-prepared CAMs reveals a modified voltage-composition curve upon Li (de)intercalation and improved capacity retention, with the largest specific capacity after 110 cycles obtained for 2.2 mol% Ga content. Operando XRD shows significant differences between structural details of the H2–H3 transition during charge and discharge as well as reduced volume contraction. Although the stabilizing effect of Ga on the LNO structure is clearly evident in our study, degradation upon electrochemical cycling still occurs as shown by the formation of surface rock salt-type layers and stacking faults.

The crystal structure and magnetic properties of the cubic spinel MgFeMnO4 were studied by using a series of in-house techniques along with large-scale neutron diffraction and muon spin rotation spectroscopy in the temperature range between 1.5 and 500 K. The detailed crystal structure is successfully refined by using a cubic spinel structure described by the space group Fd3̅m. Cations within tetrahedral A and octahedral B sites of the spinel were found to be in a disordered state. The extracted fractional site occupancies confirm the presence of antisite defects, which are of importance for the electrochemical performance of MgFeMnO4 and related battery materials. Neutron diffraction and muon spin spectroscopy reveal a ferrimagnetic order below TC = 394.2 K, having a collinear spin arrangement with antiparallel spins at the A and B sites, respectively. Our findings provide new and improved understanding of the fundamental properties of the ferrispinel materials and of their potential applications within future spintronics and battery devices., MgFeMnO4 crystallizes in the typical cubic spinel with cation disordering between the tetrahedra A and the octahedra B sites. Combining the in-house experiments with neutron (n0) and muon (μ+) techniques, we reveal (i) the accurate crystal structure and site occupancy of MgFeMnO4 at 300 and 500 K, (ii) clear presence of antisite defects that have importance for the compound’s electrochemical performance, and (iii) MgFeMnO4 enters into a collinear ferrimagnetic ordering below TC = 394.2 K.

The magnetic lanthanide (Ln3+) ions in the fergusonite and scheelite crystal structures form a distorted or stretched diamond lattice which is predicted to host exotic magnetic ground states. In this study, polycrystalline samples of the fergusonite orthotantalates M−LnTaO4 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er) were synthesized and then characterized using powder diffraction and bulk magnetometry and heat capacity. TbTaO4 orders antiferromagnetically at 2.25 K into a commensurate magnetic cell with →k=0, magnetic space group 14.77 (P2′1/c), and Tb moments parallel to the a axis. No magnetic order was observed in the other materials studied, leaving open the possibility of exotic magnetic states at T, N.D.K. thanks Sundeep Vema for carrying out the reactions at 1600◦C, Farheen Sayed for the SPS experiments, and James Analytis for technical advice on producing Fig.10. We acknowledge funding from the EPSRC (GrantsNo.EP/T028580/1,No.EP/R513180/1, and No. EP/M000524/1). The authors gratefully acknowledge the technical and human support provided at the Institut Laue Langevin (ILL), Grenoble, France.

International audience; LiNi0.6Mn0.2Co0.2O2 is one of the most promising positive electrode material for Li-ion batteries. Platelet-shaped particles of 17 nm and 86 nm thickness were obtained, with the required composition and a structure close to the ideal 2D layered structure (less than 5.2% Ni2+ ions in Li+ sites). The electrochemical performances and surface reactivity of the materials were characterized in Li-ion batteries and compared to that of 280 nm particles with a more conventional morphology. Post-cycling analyses revealed a particular reactivity at high potential for the platelets compared to the conventional particles. X-Ray photoelectron spectroscopy and ex situ XRD analyses were performed to characterize the composition of the positive electrode/electrolyte interface and the structural changes undergone by the three materials upon cycling respectively. This study showed that, as well as the particles’ composition, their morphology plays a significant role regarding the reactivity and the structural changes occurring during cycling at high potential.

This study presents the influence of polymorphism on the magnetic properties of Co

The ground state of the Nd${}_{2}$Zr${}_{2}$O${}_{7}$ pyrochlore oxide is a peculiar antiferromagnetic order that forms out of a spin ice, and which involves octupole degrees of freedom. Here, the authors test the robustness of this enigmatic phase by combining low-temperature magnetization measurements with neutron diffraction, and establish the field-temperature phase diagram. These results underline the remarkable stability of the antiferromagnetic phase, which is even enhanced in substituted samples. The data analysis indicates several magnetization processes corresponding to different paths in the energy landscape.

International audience; Na3PS4 is one of the most promising Na+ conductors, relevant for applications that can leverage its high ionic conductivity, such as solid-state batteries. Currently, two crystalline phases of the material have been identified, and it has been thought to melt above 500 degrees C. In contrast, based on diffraction, ab initio simulations, impedance spectroscopy, and thermal analysis, we show that Na3PS4 remains solid above this temperature and transforms to a third polymorph, gamma, exhibiting fast-ion conduction and an orthorhombic crystal structure. We show that the fast Na+-conduction is associated with rotational motion of the thiophosphate polyanions pointing to a plastic crystal. These findings are of major importance for the development and understanding of new polyanion-based solid electrolytes.

International audience; Layered oxide compositions Li3–xNaxNi2SbO6 have been prepared by solid-state synthesis. A complete solid solution is evidenced and characterized by X-ray and neutron diffraction as well as 7Li and 23Na solid-state nuclear magnetic resonance spectroscopy. The transition-metal layer is characterized by the classic honeycomb Ni2+/Sb5+ ordering, whereas a more uncommon randomly mixed occupancy of lithium and sodium is evidenced within the alkali interslab space. In situ X-ray diffraction and density functional theory calculations show that this alkali disordered feature is entropically driven. Fast cooling then appears as a synthesis root to confine bidimensional alkali glass within crystalline layered oxides.

The crystal structures of three polymorphs of Rb

Solid electrolytes are crucial for next-generation solid-state batteries, and Na3PS4 is one of the most promising Na+ conductors for such applications, despite outstanding questions regarding its structural polymorphs. In this contribution, we present a detailed investigation of the evolution in structure and dynamics of Na3PS4 over a wide temperature range 30 < T < 600 °C through combined experimental–computational analysis. Although Bragg diffraction experiments indicate a second-order phase transition from the tetragonal ground state (α, P4̅21c) to the cubic polymorph (β, I4̅3m) above ∼250 °C, pair distribution function analysis in real space and Raman spectroscopy indicate remnants of a tetragonal character in the range 250 < T < 500 °C, which we attribute to dynamic local tetragonal distortions. The first-order phase transition to the mesophasic high-temperature polymorph (γ, Fddd) is associated with a sharp volume increase and the onset of liquid-like dynamics for sodium-cations (translational) and thiophosphate-polyanions (rotational) evident by inelastic neutron and Raman spectroscopies, as well as pair-distribution function and molecular dynamics analyses. These results shed light on the rich polymorphism of Na3PS4 and are relevant for a range host of high-performance materials deriving from the Na3PS4 structural archetype.

Solid electrolytes are crucial for next generation solid state batteries and Na3PS4 is one of the most promising Na+ conductors for such applications. In this contribution, we present a detailed investigation of the evolution in structure and dynamics of Na3PS4 under the effect of temperature in the range 30 < T < 600 °C through combined experimental-computational analysis. Although x ray Bragg diffraction experiments indicate a second order phase transition from the tetragonal ground state (α, P-421c) to the cubic polymorph (β, I-43m), pair distribution function analysis in real space and Raman spectroscopy indicate remnants of tetragonal character in the range 250 < T < 500 °C which we attribute to dynamic local tetragonal distortions. The first order phase transition to the mesophasic high temperature polymorph (γ, Fddd) is associated with a sharp volume increase and the onset of liquid like diffusive dynamics for sodium-cations (translative) and thiophosphate-polyanions (rotational) evident by inelastic neutron- and Raman- spectroscopies, as well as pair-distribution function and molecular dynamics. These results shed light on the rich polymorphism in Na3PS4 and are relevant for a host of high performance materials deriving from the Na3PS4 structural archetype.

The structural and electronic properties of the rutile-type oxide $\ensuremath{\beta}\ensuremath{-}\mathrm{Pb}{\mathrm{O}}_{2}$ (plattnerite) are studied by neutron and synchrotron radiation diffraction and first-principles density functional theory (DFT) calculations. Both diffraction measurements and DFT calculations show that $\ensuremath{\beta}\ensuremath{-}\mathrm{Pb}{\mathrm{O}}_{2}$ has a $\mathrm{Ca}{\mathrm{Cl}}_{2}$-type orthorhombic structure (space group $Pnnm$) instead of the widely accepted $\ensuremath{\beta}\ensuremath{-}\mathrm{Pb}{\mathrm{O}}_{2}$ rutile-type tetragonal structure (space group $P{4}_{2}/mnm$). This symmetry lowering in $\ensuremath{\beta}\ensuremath{-}\mathrm{Pb}{\mathrm{O}}_{2}$ is a robust effect observed at ambient pressure at temperatures between 100 and 400 K. The orthorhombic symmetry rules out the possibility of a semimetallic symmetry-protected state in $\ensuremath{\beta}\ensuremath{-}\mathrm{Pb}{\mathrm{O}}_{2}$. Both diffraction measurements and DFT calculations show an anisotropy of thermal expansion, atomic vibrations, and elastic constants of $\ensuremath{\beta}\ensuremath{-}\mathrm{Pb}{\mathrm{O}}_{2}$ along the [100] and [010] directions.

Up to now, the possible occurrence of a cationic ordering on the tetrahedral sublattices of stoichiometric double scheelite-type oxides was not settled, with somewhat contradictory X-ray diffraction and optical measurements [Blasse, G.

Solid electrolytes are crucial for next generation solid state batteries and Na3PS4 is one of the most promising Na+ conductors for such applications. In this contribution, we present a detailed investigation of the evolution in structure and dynamics of Na3PS4 under the effect of temperature in the range 30 < T < 600 °C through combined experimental-computational analysis. Although x ray Bragg diffraction experiments indicate a second order phase transition from the tetragonal ground state (α, P-421c) to the cubic polymorph (β, I-43m), pair distribution function analysis in real space and Raman spectroscopy indicate remnants of tetragonal character in the range 250 < T < 500 °C which we attribute to dynamic local tetragonal distortions. The first order phase transition to the mesophasic high temperature polymorph (γ, Fddd) is associated with a sharp volume increase and the onset of liquid like diffusive dynamics for sodium-cations (translative) and thiophosphate-polyanions (rotational) evident by inelastic neutron- and Raman- spectroscopies, as well as pair-distribution function and molecular dynamics. These results shed light on the rich polymorphism in Na3PS4 and are relevant for a host of high performance materials deriving from the Na3PS4 structural archetype.

International audience; Solid electrolytes are crucial for next-generation solid-state batteries, and Na 3 PS 4 is one of the most promising Na + conductors for such applications, despite outstanding questions regarding its structural polymorphs. In this contribution, we present a detailed investigation of the evolution in structure and dynamics of Na 3 PS 4 over a wide temperature range 30 < T < 600°C through combined experimental−computational analysis. Although Bragg diffraction experiments indicate a second-order phase transition from the tetragonal ground state (α, P4̅ 2 1 c) to the cubic polymorph (β, I4̅ 3m) above ∼250°C, pair distribution function analysis in real space and Raman spectroscopy indicate remnants of a tetragonal character in the range 250 < T < 500°C, which we attribute to dynamic local tetragonal distortions. The first-order phase transition to the mesophasic high-temperature polymorph (γ, Fddd) is associated with a sharp volume increase and the onset of liquid-like dynamics for sodium-cations (translational) and thiophosphate-polyanions (rotational) evident by inelastic neutron and Raman spectroscopies, as well as pair-distribution function and molecular dynamics analyses. These results shed light on the rich polymorphism of Na 3 PS 4 and are relevant for a range host of high-performance materials deriving from the Na 3 PS 4 structural archetype.

International audience; We report spin-driven multiferroicity above 100 K in the ludwigite Cu(II) oxyborate Cu2CrBO5. Spontaneous polarization, which reaches 35 µC.m-2 at 5 K, appears below 120 K, concomitantly with an incommensurate antiferromagnetic order and complex magnetodielectric effects. In magnetically induced ferroelectrics, multiferroicity usually appears at low temperature, because of the competing magnetic exchanges needed to stabilize a magnetic spiral : the remarkably high transition temperature observed in Cu2CrBO5 originates from the presence of strong Cu-O-Cu magnetic super-exchange interactions, which are not weakened by Cu/Cr cationic disorder. Our result provides an important contribution to the search for high temperature spindriven multiferroics amongst low-dimensional cuprates.

Superionic lithium argyrodites are attractive as solid electrolytes for all-solid-state-batteries. These materials of composition Li6PS5X (X = Cl, Br, and I) exhibit structural disorder between the X−/S2− positions, with higher disorder realizing better Li+ transport. Further replacement of the sulfide by chloride anions (for the series Li7−xPS6−xClx) has been shown to increase the ionic conductivity. However, the underlying changes to the lithium substructure are still relatively unknown. Here we explore a larger range of nominal halide compositions in this material from x = 0.25 to x = 1.5 and explore the changes with neutron diffraction and impedance spectroscopy. The replacement of S2− by Cl−causes a lowered average charge in the center of the prevalent Li+ “cages”, which in turn causes weaker interactions with Li+ ions. Analysis of neutron diffraction data reveals that the increased Cl− content causes these clustered Li+ “cages” to become more interconnected, thereby increasing Li+ conductivity through the structure. This study explores the understanding of the fundamental structure–transport correlations in the argyrodites, specifically structural changes withinthe Li+ ion substructure upon changing anionic charge distribution.

For the first time, the real-time thermal activation of the NH4-omega zeolite (NH4-omega) was investigated through in situ synchrotron X-ray powder diffraction combined with neutron diffraction. The experimental approach allowed to study the precursor thermal behaviour upon heating, continuously monitoring the evolution of its structural features determined by NH4 ions and TMA calcination and dehydration processes. The activation of the precursor (H-omega sample) is fully reached at ⁓600 °C, when all the NH4 content has been released, dehydration mostly occurred and TMA degradation completed. From a structural point of view, Rietveld structural refinements highlighted relevant structural changes. In particular variations in intertetrahedral angles allowed to make hypothesis about the possible distribution of Bronsted acid sites on the framework oxygen atoms. The hypothesis was corroborated through the neutron Rietveld refinement of the deuterated and calcined omega (D-omega sample) that revealed the presence of two acid sites: D1 and D2 located on O5 and O2 framework oxygen atoms, respectively. Besides, neutron data confirmed the strong relation among framework and Bronsted acid sites geometry and short- and/or long-range interactions. In summary, non-conventional sources were successfully used to probe both activation and formation of acidic sites in omega precursor as well as determine the number and location of Bronsted sites in the deuterated omega.

The recent interest in the halide-based solid electrolytes Li3MX6 (M = Y, Er, In; X = Cl, Br, I) shows these materials to be promising candidates for solid-state battery application, due to high ionic conductivity and large electrochemical stability window. However, almost nothing is known about the underlying lithium sub-structure within those compounds. Here, we investigate the lithium sub-structure of Li3YCl6 and Li3YBr6 using temperature-dependent neutron diffraction. We compare compounds prepared by classic solid-state syntheses with a mechanochemical synthesis to shed light on the influence of the synthetic approach on the reported yttrium disorder and the resulting surrounding lithium sub-structure. This work provides a better understanding of the strong differences in ionic transport depending on the synthesis procedure of Li3MX6.

Fast-ion conductors are critical to the development of solid-state batteries. The effects of mechanochemical synthesis that lead to increased ionic conductivity in an archetypical sodium-ion conductor Na

The Front Cover shows L‐lysine amino acid adsorption on zeolite L. The role of the zeolite channels in the stabilization of the lysine absorbed and the effect of water on protein structure are elucidated at atomistic level. The stabilization of the L α‐helical conformation is related to strong H‐bonds between the tail aminogroups of lysine molecules and the Brønsted acid site as well as to complex intermolecular H‐bond system between water molecules, zeolite and amino acid. More information can be found in the Full Paper by Giada Beltrami et al.[Image: see text]

We investigate the macroscopic and microscopic physical properties of the solid solution of ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}\mathrm{AlGe}$. The series tunes from CeAlGe with its multi-$\stackrel{P\vec}{k}$ structure and a major moment in the $ab$ plane, to PrAlGe with an easy $c$-axis ferromagnetic ground state coexisting with a low density of nanoscale textured magnetic domain walls. Using AC, DC susceptibility, resistivity, specific heat, muon spin relaxation/rotation, and neutron scattering we analyze the magnetic ground state of the series. We provide further evidence supporting our previous claim for spin-glass-like properties in pure PrAlGe. With the introduction of Pr to CeAlGe the finite magnetic field required to stabilize the topological multi-$\stackrel{P\vec}{k}$ magnetic phase for $x=0$ becomes suppressed. The crossover between the two end-member ground states occurs in the vicinity of $x=0.3$, a region where we further anticipate the field-induced topological magnetic phase for $xl0.3$ to become the zero field ground state.

Polycrystalline $\mathrm{CaF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ and $\mathrm{CaC}{\mathrm{r}}_{0.5}\mathrm{F}{\mathrm{e}}_{1.5}{\mathrm{O}}_{4}$ have been investigated by elastic and inelastic neutron scattering. In agreement with previous reports, $\mathrm{CaF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$ undergoes two magnetic transitions, first to a $B$ phase, below ${T}_{\mathrm{NB}}=200\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, then to an $A$ phase, below ${T}_{\mathrm{NA}}=175\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, while substituted $\mathrm{CaC}{\mathrm{r}}_{0.5}\mathrm{F}{\mathrm{e}}_{1.5}{\mathrm{O}}_{4}$ undergoes a magnetic transition to the $B$ phase only, at ${T}_{\mathrm{N}}=125\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. Each phase corresponds to staggered antiferromagnetic chains coupled either ferromagnetically $(A$ phase) or antiferromagnetically $(B$ phase). In the $A$ phase of $\mathrm{CaF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$, inelastic scattering measurements show clearly defined gapped spin waves, which can be modeled with classical calculations, based on a simple exchange Hamiltonian following the topology of the crystal structure. In contrast, in the $B$ phase of both compounds, the interpretation of the excitation spectrum evades completely the classical approach, even at low temperature. These results are interpreted based on an interchain exchange close to the threshold between ferromagnetic and antiferromagnetic bonding geometry. This induces random interchain coupling, thus creating magnetic exchange disorder whose dominating effect is to blur out the magnetic excitation spectrum of the $B$ phase. A magnetoelastic effect, through which the interchain coupling becomes sizably ferromagnetic, and which is not observed in $\mathrm{CaC}{\mathrm{r}}_{0.5}\mathrm{F}{\mathrm{e}}_{1.5}{\mathrm{O}}_{4}$, stabilizes the $A$ phase at low temperature in $\mathrm{CaF}{\mathrm{e}}_{2}{\mathrm{O}}_{4}$.

It has recently been reported that the ordered aeschynite-type polar (Pna21) magnets RFeWO6 (R = Eu, Tb, Dy, Y) exhibit type II multiferroic properties below TN ∼ 15–18 K. Herein, we report a comprehensive investigation of the isostructural oxide DyCrWO6 and compare the results with those of DyFeWO6. The cation-ordered oxide DyCrWO6 crystallizes in the same polar orthorhombic structure and undergoes antiferromagnetic ordering at TN = 25 K. Contrary to DyFeWO6, only a very weak dielectric anomaly and magnetodielectric effects are observed at the Neel temperature and, more importantly, there is no induced polarization at TN. Furthermore, analysis of the low-temperature neutron diffraction data reveals a collinear arrangement of Cr spins but a noncollinear Dy-spin configuration due to single-ion anisotropy. We suggest that the collinear arrangement of Cr spins may be responsible for the absence of electric polarization in DyCrWO6. A temperature-induced magnetization reversal and magnetocaloric effects are ob...

International audience; The crystal and magnetic properties of honeycomb BiMnTeO6 have been studied between 1.5 and 300 K using synchrotron x-rays and neutron-scattering experiments. Commensurate magnetic ordering is observed below TN=10K, and corresponds to a noncollinear spin arrangement, with spins tilted away from the anisotropy easy-axis set by the Jahn-Teller distortion of the MnO6 octahedra. Inelastic-scattering experiments show two main nearly localized magnetic excitations, which can be well described by an exchange Hamiltonian involving weak Mn-Mn magnetic interactions and a crystal-field Hamiltonian characterizing the strong easy-axis anisotropy associated with the dz2 orbital ordering of Mn3+. The crystal-field levels can be accurately calculated, taking into account a transverse molecular field imposed by the magnetic ordering of the neighboring atoms below TN. This makes BiMnTeO6 an interesting example of a multiaxis Ising system in a self-imposed transverse magnetic field.

Mixed-valence LiVPO4F1–yOy materials were obtained for the first time over a large composition range (here 0.35 ≤ y ≤ 0.75) through a single-step solid-state synthesis. Interestingly, the competition between the ionic character of the V3+–F bond and the strong covalency of the V4+═O vanadyl bond originates complex crystal chemistry at the local scale, which allows stabilization of a solid solution between LiVPO4F and LiVPO4O despite a significant deviation from Vegard’s law for the cell parameters. A combined study using IR, Raman, and X-ray absorption spectroscopies highlights the effect of the vanadyl environment on the electronic structure of the vanadium orbitals and a fortiori the electrochemical behavior. Our results underline that the electrochemical performance of LiVPO4F1–yOy-type materials can be controlled by tuning the concentration of vanadyl-type defects, i.e., by playing on the competition between the ionic V3+–F bond and the covalent V4+═O bond.

The derivatives of the Li1−xRE5+xW8O32 series (RE = Dy–Lu) all crystallize C-centered in the monoclinic system (a = 1897–1909 pm, b = 560–562 pm, c = 1127–1152 pm, β ≈ 111.1°, Z = 2). In the crystal structures of all representatives there are atomic positions, which show a mixed occupation of Li+ and the respective RE3+ cations. For RE = Dy this ratio is determined to be 1:1, resulting in space group C2/c. For RE = Ho–Lu, two crystallographically distinguishable positions exhibit the aforementioned mixed occupation with one of these being preferably occupied with Li+ and the other with RE3+ cations, causing the inversion symmetry to be lost, thus, their structure solution is best performed non-centrosymmetrically in space group C2. Furthermore, in the overall structure a deficiency of lithium with respect to the ideal formula LiRE5W8O32 was determined by both single crystal and neutron diffraction experiments and therefore the composition can be described better as Li1−xRE5+xW8O32. The resulting excess of positive charges in the formula is compensated by a partial reduction of the tungsten cations from their highest oxidation state, which is also indicated by the dark blue, almost black color of the compounds and was supported by magnetic susceptibility and electron paramagnetic resonance (EPR) measurements.

International audience; Magnetic structure of CaFe5O7 ferrite has been studied jointly from neutron powder diffraction data and spectroscopic Mössbauer measurements in the thermal range from 5 to 500 K. This coupled work highlights three distinct magnetic domains around two specific temperatures: TM=125 K and TN=360 K. The latter corroborates the structural monoclinic-orthorhombic transition previously reported by transmission electron microscopy techniques and X-ray thermodiffractometry. Complementary heat capacity measurements have confirmed this first order transition with a sharp peak at 360 K. Interestingly, this large study has revealed a second magnetic transition associated to a spin rotation at 125 K similar to this one reported by Morin in α-Fe2O3 hematite at TM=260 K.

The temperature dependent neutron powder diffraction (NPD) and magnetization measurements of vanadium based garnet Ca 5 Ni 4 V 6 O 24 (CNVO) have been performed to explore its crystal and magnetic structures. The magnetization results illustrate two magnetic anomalies at 7 and 4 K. The Rietveld analysis of room temperature x-ray diffraction and NPD data confirms its Ia -3 d crystal structure. The temperature dependent NPD shows the emergence of magnetic reflections below 7 K whose intensity keeps on increasing with decreasing temperature down to 1.5 K. The crystal structure remains cubic down to 1.5 K. Rietveld analysis reveals that below 7 K, the Ni moments in CNVO undergo a commensurate collinear A-type antiferromagnetic ordering with propagation vector k =(0,0,0) and the per site ordered moment of Ni 2+ is 1.69±0.05 μ B . Absence of any additional magnetic or nuclear reflections below 4 K confirms that the nuclear and magnetic structures remain invariant across the 4 K magnetic anomaly.

Layered oxide compositions Li