Ruddlesden-Popper-type compounds are particularly attractive electrode materials for fluoride-ion batteries. Among them, LaSrMnO4 has received significant attention due to its high fluoride incorporation capability and lower environmental impact compared to nickel- and cobalt-based analogues. In this work, neutron diffraction data are used to provide an experimental visualization of fluoride-ion diffusion in this class of materials, through maximum entropy method (MEM) and bond valence site energy (BVSE) analysis. Additionally, since oxygen excess is well known in Ruddlesden-Popper oxides but its impact on fluoride-ion transport has not been previously investigated, molecular dynamics (MD) simulations were employed to reveal how oxygen over-stoichiometry affects fluoride intercalation mechanisms and energetics, unveiling new migration pathways that hinder fluoride mobility. These findings have direct implications for fluoride-ion battery performance, highlighting the critical role of oxygen content in determining anion transport and the electrochemical performance of this class of materials.

Lithium argyrodites hold great promise as solid electrolytes for all-solid-state batteries (ASSBs) owing to their high room-temperature ionic conductivity and soft mechanical properties. However, their poor air stability hinders large-scale commercial applications. To overcome this, we demonstrate herein a high-entropy design strategy by substituting the P-site in Li6PS5I with Ge, Sb, Si, and As, yielding Li6.5As0.25Si0.25Ge0.25Sb0.25S5I with a configurational entropy of 2.04R. Neutron powder diffraction (NPD) and various spectroscopic analyses indicate that the compositional complexity increases structural (occupational) disorder and facilitates lithium transport, resulting in room-temperature ionic conductivities of 8.0 mS cm-1 in cold-pressed state and 11.4 mS cm-1 for hot-pressed pellets, the latter being significantly higher compared to the glassy counterpart Li6PS5I (1.5 mS cm-1). HEA-As0.25 also demonstrates much improved chemical stability against moist air and toluene. When integrated into full cells with a sulfur cathode and an In/InLi anode, the respective all-solid-state lithium-sulfur batteries exhibit excellent cycling stability. Overall, this work provides a new approach for designing advanced sulfide solid electrolytes that simultaneously possess high ionic conductivity and air stability.

Nitridometallates with extended anionic frameworks exhibit a variety of intriguing electronic properties, including band magnetism, metal-metal bonding, and superconductivity. Such extended framework materials are scarce with late transition metals due to the requirement of high metal oxidation states and nitrogen content. This study presents a family of nitridocobaltates LnCo2N2 (Ln = La, Pr, Nd) with an extended layered cobalt-nitrogen network related to the Kagome lattice that was synthesized at 8 GPa in a large volume press. The compounds crystallize in the trigonal space group R 3 ¯ $\bar 3$ with alternating layers of unusual trigonal planar CoN3 and octahedral LnN6 polyhedra. Magnetization and powder neutron diffraction studies indicate a metallic ground state and the suppression of magnetic ordering of the rare earth moments due to their arrangement on a trigonal lattice. The compounds have a surprising mixed-valent Co+I/+II state, which is high for nitridocobaltates. This study demonstrates the structural diversity available in late nitridometallates via high-pressure synthesis, which can now be explored systematically.

The thermal oxidation of stoichiometric La2CoO4.00 was investigated using in situ neutron and powder X-ray diffraction in air, complemented by thermogravimetric analysis (TGA). The process involves the topotactic insertion of extra oxygen atoms into interstitial lattice sites, forming La2CoO4+δ. Oxygen uptake is initiated above 320 K, leading to a sequence of phase transitions as a function of temperature (T) and oxygen excess (δ). The structural evolution starts from an orthorhombic phase at δ = 0, with a transition to a tetragonal phase for 0.05 ≤ δ ≤ 0.17, and proceeds through two distinct orthorhombic phases, both exhibiting long-range oxygen ordering above 525 K. The maximum oxygen concentration, observed above 680 K, corresponds to La2CoO4.263. The resulting phase diagram reveals rapid oxygen diffusion and ordering kinetics, accompanied by subtle structural modifications as a function of δ. Notably, the long-range oxygen order remains stable over a wide temperature range. Each phase was structurally characterized by using Rietveld refinement.

We introduce NaI as a mild reagent for low-temperature topochemical defluorination of Ruddlesden-Popper oxyfluorides. In a topochemical fluorination and subsequent defluorination process La2CoO3F3 is obtained from La2CoO4, using poly(vinylidene fluoride) (PVDF) or polytetrafluoroethylene (PTFE) as fluorine sources, and converted to La2CoO3F2 by the addition of NaI. Both processes were studied by laboratory in situ X-ray diffraction, which reveals a stepwise fluorine uptake through four crystalline intermediates. Subsequent NaI treatment enables controlled F- removal to form La2CoO3F2. This Co(II) phase is not accessible by direct topochemical fluorination of La2CoO4 and is not observed along the La2CoO3F3 formation pathway. X-ray and neutron powder diffraction establish La2CoO3F3 as monoclinic (P21/c) with full occupation of the interstitial anion layer, whereas La2CoO3F2 is isotypic to La2NiO3F2 (Cccm) and exhibits a channel-like interstitial anion arrangement. Thermal analysis by in situ XRD is used to scan the temperature ranges over which both oxyfluorides retain their structure, and magnetization measurements indicate the change in cobalt oxidation and spin state upon fluorination/defluorination. This study uses the La2CoO4 → La2CoO3F3 → La2CoO3F2 reaction sequence as model system to demonstrate that, sequential topochemical fluorination and NaI-mediated defluorination provides access to metastable, anion-ordered RP oxyfluorides under milder conditions than conventional hydride-based reductions, avoiding both reduction of the metal cations to their metallic state and anion substitution reactions due to size effects of the iodide ion.

The solvothermal synthesis of polycrystalline cubic CsMnF3 at 100 °C is reported, a phase previously prepared phase-pure only at 700 °C and 30 kbar. In situ powder X-ray diffraction, shows that cubic CsMnF3 transforms irreversibly to the 6H polymorph at ∼500 °C. The magnetic properties of cubic CsMnF3 are characterised by G-type antiferromagnetic ordering, as determined from powder neutron diffraction.

Two new hydrides, respectively deuterides, of the FeB-type CeSi were synthesized, and their reaction as well as magnetic behavior and structures were studied. Hydrogenation leads to two phases, a kinetic product retaining the FeB structure with hydrogen-filled tetrahedra (LaGeH type, Pnma, P-phase: CeSiD0.82(2)) and the thermodynamically preferred hydrogen-filled CrB-type structure (ZrNiH type, Cmcm, C-phase: CeSiD0.96(1)). Both hydrides are ferromagnets and feature Curie temperatures of 22.4(1) K (C-phase) and 24.3(1) K (P-phase), which are exceptionally high for cerium intermetallics. The effective magnetic moments of μ(Ce3+) = 2.53 μB are very close to the free ion value of 2.54 μB. The compounds were studied using in situ neutron powder diffraction and magnetic characterization and by density functional theory and chemical bonding analysis.

We discover a rare structural manifestation of the Goldstone paradigm in a hexagonal polytype of the prototypical ferroelectric BaTiO_{3}. First-principles calculations confirm the Goldstone character of the order parameter, while our high-resolution diffraction measurements unveil an unusual reentrant Goldstone regime manifesting as a quasicontinuous domain texture in the vicinity of the ferroelectric transition. We develop a minimal Landau model that encapsulates these observations, illustrating how U(1) symmetry can be restored at the ferroelectric transition. Our findings demonstrate how exotic Goldstone physics can be unlocked in systems dominated by highly anharmonic interactions, presenting a promising pathway to stabilize emergent polar topologies in bulk materials.

γ-Ba_3 CoNb_2 O_9 realizes a disordered simple-cubic spin-1/2 lattice in which Co^2+ ions randomly occupy one third of the sites, placing the system close to the site-percolation threshold for magnetic order. Specific-heat, susceptibility, neutron spin-echo, and muon spin-rotation measurements reveal a broad thermodynamic crossover, short-range magnetic correlations, and persistent fast spin dynamics down to at least 0.1 K, with no evidence for static order or conventional spin-glass freezing. Monte Carlo simulations yield a broad distribution of orphan spins, finite clusters, and an infinite network. The calculated orphan-spin fraction (≈ 8.8%) agrees well with the weakly correlated spin fraction inferred from magnetization (≈ 8.2%). Exact diagonalization of a diluted S = 1/2 Heisenberg model captures the broad magnetic specific-heat anomaly and supports the coexistence of weakly and strongly correlated spin environments. These results support a picture in which spin-1/2 quantum fluctuations, together with dilution and proximity to the percolation threshold, can support a disorder-driven dynamical state with short-range correlations in three dimensions, distinct from both classical spin glasses and geometrically frustrated quantum spin liquids.

We report a comprehensive study of the structural and magnetic properties of CuCoFe2O5, a CaFe3O5-type mixed-metal oxide obtained at 20 GPa and 1000 degrees C. Room-temperature single-crystal and powder diffraction measurements confirm the orthorhombic Cmcm framework, with Cu2+ occupying a distorted CuO4+2 trigonal prismatic site and Co2+/Fe3+ residing in edge- and corner-sharing octahedral environments. Bond valence and anisotropic displacement analyses reveal pronounced local distortions around Cu2+, consistent with Jahn-Teller activity. Magnetic measurements indicate two successive transitions: a high-temperature antiferromagnetic order at T N1 = 195 K and a low-temperature spin reorientation at T N2 = 77 K of structural origin, the latter accompanied by a strong bifurcation between field- and zero-field-cooled magnetization curves. Neutron diffraction and DFT+U calculations demonstrate that the magnetic structure comprises competing Fe-Fe, Fe-Co, and Co-Cu interactions, leading to a canted ferrimagnetic state at low temperature. Moderate magnetic frustration (f approximate to 3.6) and strong spin-orbit coupling of Co2+ stabilize large coercivity (similar to 6.7 T at 2 K). These results highlight the intricate interplay between structural distortions, cation disorder, and competing exchange pathways in determining the complex magnetic ground state of CuCoFe2O5.

The simultaneous presence of hydride (H-) and oxide (O2-) anions in an inorganic material is thermodynamically challenging. Oxyhydrides have always been synthesized from an oxide precursor, by using high-temperature solid-state reaction using a mixture of oxide and hydride, topochemical reduction at mild temperatures, or high-pressure synthesis. Here, we introduce a novel and unprecedented synthesis route for transition metal oxyhydrides, where the starting material is not an oxide but an intermetallic compound, LaScSi. The topochemical synthesis of LaScSiOxHy (x ≈ 0.5, y ≈ 1) occurs through water dissociation, highlighting the exceptional catalytic behavior of the electride-type parent material. The topochemical insertion of oxygen and hydrogen transforms LaScSi into a more two-dimensional material and modifies its electronic properties, altering its transport properties, from three-dimensional metallic to semimetallic. This innovative path to oxyhydrides is also of fundamental interest for catalysis: it could open the way for new methods of hydrogen production and storage, especially in water splitting, bypassing traditional processes such as electrolysis or photocatalysis.

Hexagonal perovskite derivatives such as Ba7Nb4MoO20 and Ba3NbMoO8.5 have recently been reported to exhibit high oxide ion conductivity and have potential applications in next-generation solid oxide fuel cells. In contrast, Ba3V2O8 and Sr3V2O8 that crystallize with the structurally related palmierite structure show oxide ion conductivities orders of magnitude lower. Here we use design principles to enhance the oxide ion conductivity in palmierites. By replacing V5+ with two cations that are known to display flexible coordination (Mo6+ and Ti4+) and manipulating the ratio of Mo6+:Ti4+ to insert interstitial oxygen, a high oxide ion conductivity of 3.96 × 10-3 S cm-1 at 600 °C is observed in Ba3Ti0.9Mo1.1O8.1, two orders of magnitude higher than previously reported in palmierites. The oxide ion conductivity of Ba3Ti0.9Mo1.1O8.1 is also higher than that previously reported for both Ba7Nb4MoO20 and Ba3NbMoO8.5 at 600 °C. Introducing interstitial oxygen into the [BaO2+x] layer results in a change in the oxide ion transport from a cog-wheel type motion to an interstitialcy mechanism, demonstrating that palmierites are flexible to doping strategies via the introduction of either vacancies or oxide ion interstitials.

In this contribution we report on the synthesis, structure and optical characterization of Ruddlesden-Popper oxyfluorides La2Ni1-xCuxO2.5F3 (0 <= x <= 1) obtained by topochemical low-temperature fluorination of La2Ni1-xCuxO4 with polyvinylidene fluoride (PVDF). Our study reveals that the anionic ordering in the tetragonal unit cell of La2NiO2.5F3 persists even at high Cu substitution levels (x = 0.9), with minimal change in unit cell volume. This observation is contrary to expectations based on Jahn-Teller induced unit cell distortions, which were previously reported for the oxides La2Ni1-xCuxO4, as well as for the closely related oxyfluorides La2Ni1-xCuxO3F2. The pure copper-containing compound La2CuO2.5F3 crystallizes in a triclinic version of the same structure, and the symmetry lowering is attributed to the enhanced space requirements of the Jahn-Teller elongated CuO4F2 octahedra. The structural investigations based on XRD and ND Rietveld refinements are supported by low-field 19F MAS NMR experiments. We also report the results of diffuse reflectance UV-Vis measurements, which are complemented by DFT calculations. Here, we demonstrate a strong impact of the Cu substitution on the electronic structure of the oxyfluorides, resulting in band gap energies in the range of 3.4 eV to 1.3 eV, spanning the whole visible spectrum. Notably, first photocatalytic water splitting tests reveal a considerable hydrogen evolution activity for x = 0.2, highlighting the potential of Ruddlesden-Popper oxyfluorides for solar energy applications.

Murunskite (K 2 FeCu 3 S 4 ) bridges the two known families of high‐temperature superconductors, cuprates and iron‐pnictides, structurally and electronically. Like these families, murunskite exhibits an antiferromagnetic (AF)‐like response with an ordered phase below 97 K. The magnetic iron atoms are randomly distributed over one‐quarter of the sites in two‐dimensional planes, while the remaining sites are occupied by non‐magnetic copper, evoking the notion of a high‐entropy magnetic alloy. This intriguing magnetic transition is studied by neutron, Mössbauer, and X‐ray photoelectron spectroscopy (XPS) measurements on single crystals. The AF order has a nearly commensurate quarterzone wave vector. In the paramagnetic state, Mössbauer spectroscopy identifies two iron sites, associated with Fe 3 + or Fe 2 + oxidation states as observed by XPS, which merge into a third site upon cooling, indicating an orbital transition. This cascade of local transitions transforms iron atoms from a fully orbitally and magnetically disordered state to a homogeneously ordered state in inverse space, while still being randomly distributed in real space. This finding challenges the traditional paradigm of magnetism in insulators, which relies on a direct connection between crystal structure and the location of magnetic moments.

Kurzzusammenfassung Nitridische Perovskite sind eine kürzlich erschlossene Materialklasse mit einer begrenzten Anzahl stabiler Verbindungen. Besonders selten kommen Materialien mit geordneten Anionen‐Fehlstellen wie Nitride vom LaNiO 2 ‐Typ vor, obwohl für analoge Oxide nützliche Eigenschaften wie Supraleitung beschrieben wurden. In dieser Arbeit stellen wir die Hochdruck‐ und Hochtemperatur‐Synthese zweier Ln ReN 2 ‐Verbindungen ( Ln = Pr, Nd) mit verzerrter LaNiO 2 ‐Struktur vor. Röntgen‐Pulverdiffraktometrie und Neutronenbeugung zeigen eine orthorhombische Verzerrung (o‐ Ln ReN 2 ) der LaNiO 2 ‐Aristotyp‐Struktur, die durch ein Buckling der ReN 4/2 ‐Schichten infolge einer Re‐Dimerisierung verursacht wird. Eine Analyse der elektronischen Struktur zeigt, dass die o‐ Ln ReN 2 ‐ Materialen aus klassischen Nitridometallat‐Anionen und einem kationischen intermetallischen Gerüst bestehen. Die Re‐Dimerisierung resultiert wahrscheinlich aus einer elektronischen Instabilität, die mit einer Peierls‐artigen Verzerrung zusammenhängt. Des Weiteren charakterisieren wir mithilfe magnetischer Messungen sowie magnetischer Neutronenstreuung den magnetischen Grundzustand beider Materialien und decken dabei eine langreichweitige antiferromagnetische Ordnung der Nd 3+ ‐Momente in NdReN 2 bei T N = 15.5 K auf. Die Stabilität der Verbindungen wird durch temperaturabhängige Röntgen‐Pulverdiffraktometrie untersucht, die eine Zersetzung von NdReN 2 bei ca. 750 °C zeigt. Die o‐LnReN 2 ‐Materialien stellen eine bemerkenswerte Klasse von Nitriden an der Grenze zwischen klassischen Nitridometallaten, intermetallischen Verbindungen und niedrigdimensionaler Komplexchemie dar.

The feasibility of chemical doping of a double double perovskite (DDPv) is demonstrated by LaxCa1-xMnMnReO6 solid solutions in which cation-site ordering is preserved to x ≥ 0.5 while La3+/Ca2+ substitution at one site tunes magnetic properties. Each of the ∼20 DDPv's discovered by high pressure synthesis in recent years is thus a starting point for chemical tuning to discover and tune electronic and magnetic properties.

Tunability of the band gap energy is achieved for the highly fluorinated system La 2 Ni 1− x Cu x O 2.5 F 3 while retaining the overall structural distortion.

Excitonic insulators are a remarkable class of insulators that can exhibit a condensate of electron-hole pairs below a critical temperature T C and are predicted to give rise to exotic quantum phenomena. Thus far, the excitonic insulator phase has been predominantly explored in chalcogenide-based systems. However, the nature of the excitonic order parameter governing the EI transitions in these candidate systems is still controversial as there are few candidate materials that exhibit an EI phase without an accompanying symmetry-breaking lattice distortion. The discovery of new chemical systems that can host the EI phase is hence very important. Here we report evidence of a tuneable, bulk correlated interlayer excitonic insulator in the oxypnictide CeMnAsO 1 − x F x ( x ≥ 0.035) with a maximum T C of 104 K. Crucially, no symmetry-breaking lattice distortion or charge density wave is observed across the transition which will enable further study of the EI phase diagram. The proposed excitonic insulator (EI) phase emerges when the electronic band gap is tuned below a critical threshold through chemical doping and is marked by a significant upturn in the resistivity. First-principles calculations reveal the formation of bound excitons between spatially separated electrons and holes in distinct layers within the crystal structure with a binding energy, E b = 50 meV. A reversal in the Hall and Seebeck coefficients is observed below T C as holes from the CeO/F layer bind with electrons in the Mott insulating As-Mn-As block. Neutron diffraction shows that T C can be further controlled by reducing the interlayer distance and enhancing the electronic coupling between layers. This work identifies CeMnAsO 1 − x F x as a promising chemical platform for exploring novel quantum phases arising from excitons and expands the range of materials considered to host the EI phase.

Among the orthochromites comprising a magnetic rare-earth constituent, CeCrO 3 exhibits the highest Néel temperature of ∼ 260 K . Using high-resolution neutron powder diffraction, we redetermined the low-temperature antiferromagnetic Cr and Ce magnetic moment configuration in CeCrO 3 . The Cr moments order with a weakly canted G -type antiferromagnetic structure ( Γ 2 ) where the moments essentially align along the b axis ( P n m a setting of the space group No. 62). Very weak Ce magnetic coherent scattering appears below ∼ 22 K due to a C x -type ordering of the Ce moments ( μ Ce ≈ 0.06 μ B ). From the temperature dependence of the lattice parameters, we analyze the volume magnetoelastic effects which cause a contraction of the cell volume on ordering of the Cr moments. Below ∼ 150 K a subtle but continuous adjustment of the a and c lattice parameters takes place which is attributed to a spin reorientation of the Cr magnetic moments. The temperature dependence of the Cr magnetic order parameter indicates a gap in the magnon spectrum. We reanalyze the specific heat capacity of CeCrO 3 which at low temperatures exhibits additional contributions due to thermal excitation within the crystal-field split levels of the Ce 3 + F 5 / 2 2 Hund's rule ground state. A model calculation of the magnetization including magnetic polarization of the Ce moments is consistent with a spin reorientation of the Cr magnetic moments.