Topochemical Reaction Involving Double-to-Single Layer Conversion: MoTaON with a Kagomé Lattice.

Topochemical reactions in transition metal oxides, typically involving oxygen removal or anion exchange, provide a versatile platform for creating metastable phases with diverse functionalities. While these reactions often modify the valence and coordination environment of transition metals, the underlying metal frameworks are usually preserved, maintaining a 1:1 structural correspondence. A representative example is SrFeO → SrFeO, in which each octahedral layer transforms into a single square-planar layer.

Fluorine as a Key Element in Solid-State Chemistry of Mixed Anions 3d Transition Metal-Based Materials for Electronic Properties and Energy.

Mixed anion compounds containing fluorine and based on 3d transition elements represent a class of materials with significant interest in solid-state chemistry. Indeed, their highly varied chemical composition, structural diversity, and the resulting electronic properties provide a rich playground for imagining new applications in the field of energy. The anions and the chemical bonds they form with the 3d transition elements are at the heart of this review.

Structure Transformation of Methylammonium Polyoxomolybdates via In-Solution Acidification and Solid-State Heating from Methylammonium Monomolybdate and Application as Negative Staining Reagents for Coronavirus Observation.

We prepared polyoxomolybdates with methylammonium countercations from methylammonium monomolybdate, (CHNH)[MoO], through two dehydrative condensation methods, acidifying in the aqueous solution and solid-state heating. Discrete (CHNH)[MoO(OH)(HO)], polymeric ((CHNH)[MoO(HO)]), and polymeric ((CHNH)[γ-MoO]) were selectively isolated via pH control of the aqueous (CHNH)[MoO] solution. The HSO-acidified solution of pH < 1 produced "sulfonated α-MoO", polymeric ((CHNH)[(MoO)(SO)]).

Mechanochemical Synthesis of Perovskite Oxyhydrides: Insights from Shear Modulus.

Perovskite oxyhydrides have attracted recent attention due to their intriguing properties such as ionic conductivity and catalysis, but their repertoire is still restricted compared to perovskite oxynitrides and oxyfluorides. Historically, perovskite oxyhydrides have been prepared mostly by topochemical reactions and high-pressure (HP) reactions, while in this study, we employed a mechanochemical (MC) approach, which enables the synthesis of a series of OH-type oxyhydrides, including those with the tolerance factor () much smaller than 1 (e.g.

Construction of Ideal One-Dimensional Spin Chains by Topochemical Dehydration/Rehydration Route.

One-dimensional (1D) Heisenberg antiferromagnets are of great interest due to their intriguing quantum phenomena. However, the experimental realization of such systems with large spin remains challenging because even weak interchain interactions induce long-range ordering. In this study, we present an ideal 1D = 5/2 spin chain antiferromagnet achieved through a multistep topochemical route involving dehydration and rehydration.

Thermal multiferroics in all-inorganic quasi-two-dimensional halide perovskites.

Multiferroic materials, particularly those possessing simultaneous electric and magnetic orders, offer a platform for design technologies and to study modern physics. Despite the substantial progress and evolution of multiferroics, one priority in the field remains to be the discovery of unexplored materials, especially those offering different mechanisms for controlling electric and magnetic orders. Here we demonstrate the simultaneous thermal control of electric and magnetic polarizations in quasi-two-dimensional halides (K,Rb)MnCl, arising from a polar-antipolar transition, as evidenced using both X-ray and neutron powder diffraction data.

Large Perpendicular Magnetic Anisotropy Induced by an Intersite Charge Transfer in Strained EuVOH Films.

Perovskite oxides O continue to be a major focus in materials science. Of particular interest is the interplay between and cations as exemplified by intersite charge transfer (ICT), which causes novel phenomena including negative thermal expansion and metal-insulator transition. However, the ICT properties were achieved and optimized by cationic substitution or ordering.

Potassium-rich antiperovskites KHTe and KFTe and their structural relation to lithium and sodium counterparts.

Unlike perovskite oxides, antiperovskites MHCh and MFCh (M = Li, Na; Ch = S, Se, Te) mostly retain their ideal cubic structure over a wide range of compositions owing to anionic size flexibility and low-energy phonon modes that promote their ionic conductivity. In this study, we show the synthesis of potassium-based antiperovskites KHTe and KFTe and discuss the structural features in comparison with lithium and sodium analogues. It is shown experimentally and theoretically that both compounds maintain a cubic symmetry and can be prepared at ambient pressure, in contrast to most of the reported MHCh and MFCh which require high pressure synthesis.

Pressure-Induced Anion Order-Disorder Transition in Layered Perovskite SrLiHOCl.

While cation order-disorder transitions have been extensively investigated because of their decisive impact on chemical and physical properties, only few anion order-disorder transitions are known. Here, we show that SrCuOCl-type layered perovskite SrLiHOCl exhibits a pressure-induced H/O order-disorder transition. When synthesized at ambient and low pressures (≤2 GPa), SrLiHOCl is isostructural to orthorhombic EuLiHOCl () with a H/O order at the equatorial sites.

Structural Transformation in LnHS (Ln = La, Nd, Gd, and Er) with Coordination Change between an S-Centered Octahedron and a Trigonal Prism.

Lanthanide hydride chalcogenides LnHSe and LnHTe (Ln = lanthanides) crystallize in two polymorphs, 2H and 1H structures (ZrBeSi-type and filled-WC-type structures, respectively), but the chemical origin of the structural selection is unknown. Here, we have expanded the LnHCh (Ch = O, Se, and Te) family to include LnHS (Ln = La, Nd, Gd, and Er) using high-pressure synthesis. LnHS adopts the 2H structure for large Ln (La, Nd, and Gd) and the 1H structure for small Er.

Evolutionary Algorithm Directed Synthesis of Mixed Anion Compounds LaF X (X=Br, I) and LaFI.

Mixed-anion compounds have attracted growing attentions, but their synthesis is challenging, making a rational search desirable. Here, we explored LaF -LaX (X=Cl, Br, I) system using ab initio structure searches based on evolutionary algorithms, and predicted LaF X and LaFX (X=Br, I), which are respectively isostructural with LaHBr and YH I, consisting of layered La-F blocks with single and double ordered honeycomb lattices, separated by van der Waals gaps. We successfully synthesized these compounds: LaF Br and LaFI crystallize in the predicted structure, while LaF I is similar to the predicted one but with different layer stacking.

Topochemical Synthesis of Ca CrN H Involving a Rotational Structural Transformation for Catalytic Ammonia Synthesis.

Topochemical reactions have led to great progress in the discovery of new metastable compounds with novel chemical and physical properties. With these reactions, the overall crystal structure of the host material is generally maintained. Here we report a topochemical synthesis of a hexagonal nitride hydride, h-Ca CrN H, by heating an orthorhombic nitride, o-Ca CrN , under hydrogen at 673 K, accompanied by a rotational structural transformation.

Highly Electron-Doped TaON Single-Crystal Growth by a High-Pressure Flux Method.

Transition-metal oxynitrides have a variety of functions such as visible light-responsive catalysts and dielectric materials, but acquiring single crystals necessary to understand inherent properties is difficult and is limited to relatively small sizes (<10 μm) because they easily decompose at high temperatures. Here, we have succeeded in growing platelet single crystals of TaON with a typical size of 50 × 100 × 10 μm under a high pressure and high temperature (6 GPa and 1400 °C) using a LiCl flux. Such a harsh condition, in contrast to powder samples synthesized under mild conditions, resulted in the introduction of a large amount of oxygen vacancies ( = 0.

Polyoxocationic antimony oxide cluster with acidic protons.

The success and continued expansion of research on metal-oxo clusters owe largely to their structural richness and wide range of functions. However, while most of them known to date are negatively charged polyoxometalates, there is only a handful of cationic ones, much less functional ones. Here, we show an all-inorganic hydroxyiodide [HSbO][HSbIO][SbI]·25HO (), forming a face-centered cubic structure with cationic SbO clusters and two types of anionic clusters in its interstitial spaces.

Lone-Pair-Induced Intra- and Interlayer Polarizations in Sillén-Aurivillius Layered Perovskite BiNbOBr.

Sillén-Aurivillius layered perovskite oxyhalides BiO ( = Nb, Ta; = Cl, Br) are of great interest because of their potential as lead-free ferroelectrics in addition to their function as visible-light-responsive photocatalysts. In this work, we revisited the crystal structure of BiNbOBr (space group: 2), revealing that the intralayer polarization is not based on the reported NbO octahedral tilting but is derived from the stereochemically active Bi lone pair electrons (LPEs) and the octahedral off-centering of Nb cations. The revised structure (space group: ) has additional interlayer polarizations (calculated: 0.

Dehydration of Electrochemically Protonated Oxide: SrCoO with Square Spin Tubes.

Controlling oxygen deficiencies is essential for the development of novel chemical and physical properties such as high- superconductivity and low-dimensional magnetic phenomena. Among reduction methods, topochemical reactions using metal hydrides (e.g.

BiOCl ( = Ba, Sr, Ca) with Double and Triple Fluorite Layers for Visible-Light Water Splitting.

Layered oxyhalides containing double or triple fluorite layers are promising visible-light-responsive water-splitting photocatalysts with unique band structures. Herein, we report on the synthesis, structure, and photocatalytic property of BiBaOCl (4/) with alternating double (BiO) and triple (BiBaO) fluorite layers, which was extracted from the crystallographic database on the basis of Madelung potential calculations. Rietveld refinements from powder X-ray and neutron diffraction data revealed the presence of cationic disorder between BiO and BiBaO layers, leading to electrostatic stabilization.

Mixed alkali-ion transport and storage in atomic-disordered honeycomb layered NaKNiTeO.

Honeycomb layered oxides constitute an emerging class of materials that show interesting physicochemical and electrochemical properties. However, the development of these materials is still limited. Here, we report the combined use of alkali atoms (Na and K) to produce a mixed-alkali honeycomb layered oxide material, namely, NaKNiTeO.

Enhanced Magnetic Interaction by Face-Shared Hydride Anions in 6H-BaCrOH.

Studies on magnetic oxyhydrides have been almost limited to perovskite-based lattices with corner-sharing octahedra with a M-H-M (M: transition metal) angle of θ ∼ 180°. Using a high-pressure method, we prepared BaCrOH with a 6H-type hexagonal perovskite structure with corner- and face-sharing octahedra, offering a unique opportunity to investigate magnetic interactions based on a θ ∼ 90° case. Neutron diffraction for BaCrOH revealed an antiferromagnetic (AFM) order at ∼ 375 K, which is higher than ∼240 K in BaCrOF.

Alkali-Rich Antiperovskite MFCh (M = Li, Na; Ch = S, Se, Te): The Role of Anions in Phase Stability and Ionic Transport.

To improve ionic conductivity, solid-state electrolytes with polarizable anions that weakly interact with mobile ions have received much attention, a recent example being lithium/sodium-rich antiperovskite MHCh (M = Li, Na; Ch = S, Se, Te). Herein, in order to clarify the role of anions in antiperovskites, the MFCh family, in which the polarizable H anion at the octahedral center is replaced by the ionic F anion, is investigated theoretically and experimentally. We unexpectedly found that the stronger attractive interaction between F and M ions does not slow down the M ion diffusion, with the calculated energy barrier being as low as that of MHCh.

Anion ordering enables fast H conduction at low temperatures.

The introduction of chemical disorder by substitutional chemistry into ionic conductors is the most commonly used strategy to stabilize high-symmetric phases while maintaining ionic conductivity at lower temperatures. In recent years, hydride materials have received much attention owing to their potential for new energy applications, but there remains room for development in ionic conductivity below 300°C. Here, we show that layered anion-ordered BaH ( = Cl, Br, and I) exhibit a remarkable conductivity, reaching 1 mS cm at 200°C, with low activation barriers allowing H conduction even at room temperature.

Formation of PbCl-type AHF (A = Ca, Sr, Ba) with partial anion order at high pressure.

The high-pressure structures of alkaline earth metal hydride-fluorides (AHFs) (A = Ca, Sr, Ba) were investigated up to 8 GPa. While AHF adopts the fluorite-type structure (Fm3[combining macron]m) at ambient pressure without anion ordering, the PbCl2-type (cotunnite-type) structure (Pnma) is formed by pressurization, with a declining trend of critical pressure as the ionic radius of the A2+ cation increases. In contrast to PbCl2-type LaHO and LaOF whose anions are fully ordered, the H-/F- anions in the high-pressure polymorph of SrHF and BaHF are partially ordered, with a preferential occupation of H- at the square-pyramidal site (vs.

Spin Frustration in Double Perovskite Oxides and Oxynitrides: Enhanced Frustration in LaMnTaON with a Large Octahedral Rotation.

The B-site sublattice in the double perovskite oxides ABB'O (B: magnetic cation; B': nonmagnetic cation) causes spin frustration, but the relationship between the structure and spin frustration remains unclear although a number of compounds have been studied. The present study systematically investigated AMnB'O ( = 5/2) and found that the frustration factor, defined by = |θ|/ (θ: Weiss temperature; : Néel temperature), scales linearly with the tolerance factor , i.e.