Octahedral Layers Research Articles

Control of Polarity in Kagome‐NiAs Bismuthides

AbstractA 2×2×1 superstructure of the P63/mmc NiAs structure is reported in which kagome nets are stabilized in the octahedral transition metal layers of the compounds Ni0.7Pd0.2Bi, Ni0.6Pt0.4Bi, and Mn0.99Pd0.01Bi. The ordered vacancies that yield the true hexagonal kagome motif lead to filling of trigonal bipyramidal interstitial sites with the transition metal in this family of “kagome‐NiAs” type materials. Further ordering of vacancies within these interstitial layers can be compositionally driven to simultaneously yield kagome‐connected layers and a net polarization along the c axes in Ni0.9Bi and Ni0.79Pd0.08Bi, which adopt Fmm2 symmetry. The polar and non‐polar materials exhibit different electronic transport behaviour, reflecting the tuneability of both structure and properties within the NiAs‐type bismuthide materials family.

Control of Polarity in Kagome-NiAs Bismuthides.

A 2×2×1 superstructure of the P63/mmc NiAs structure is reported in which kagome nets are stabilized in the octahedral transition metal layers of the compounds Ni0.7Pd0.2Bi, Ni0.6Pt0.4Bi, and Mn0.99Pd0.01Bi. The ordered vacancies that yield the true hexagonal kagome motif lead to filling of trigonal bipyramidal interstitial sites with the transition metal in this family of "kagome-NiAs" type materials. Further ordering of vacancies within these interstitial layers can be compositionally driven to simultaneously yield kagome-connected layers and a net polarization along the c axes in Ni0.9Bi and Ni0.79Pd0.08Bi, which adopt Fmm2 symmetry. The polar and non-polar materials exhibit different electronic transport behaviour, reflecting the tuneability of both structure and properties within the NiAs-type bismuthide materials family.

Disorder and Halide Distributions in Cesium Lead Halide Nanocrystals as Seen by Colloidal 133Cs Nuclear Magnetic Resonance Spectroscopy.

Colloidal nuclear magnetic resonance (cNMR) spectroscopy on inorganic cesium lead halide nanocrystals (CsPbX3 NCs) is found to serve for noninvasive characterization and quantification of disorder within these structurally soft and labile particles. In particular, we show that 133Cs cNMR is highly responsive to size variations from 3 to 11 nm or to altering the capping ligands on the surfaces of CsPbX3 NCs. Distinct 133Cs signals are attributed to the surface and core NC regions. Increased heterogeneous broadening of 133Cs signals, observed for smaller NCs as well as for long-chain zwitterionic capping ligands (phosphocholines, phosphoethanol(propanol)amine, and sulfobetaines), can be attributed to more significant surface disorder and multifaceted surfaces (truncated cubes). On the contrary, capping with dimethyldidodecylammonium bromide (DDAB) successfully reduces signal broadening owing to better surface passivation and sharper (001)-bound cuboid shape. DFT calculations on various sizes of NCs corroborate the notion that the surface disorder propagates over several octahedral layers. 133Cs NMR is a sensitive probe for studying halide gradients in mixed Br/Cl NCs, indicating bromide-rich surfaces and chloride-rich cores. On the contrary, mixed Br/I NCs exhibit homogeneous halide distributions.

Elucidating the Non-Covalent Interactions that Trigger Interdigitation in Lead-Halide Layered Hybrid Perovskites.

Two-dimensional (2D) hybrid organic-inorganic perovskites constitute a versatile class of materials applied to a variety of optoelectronic devices. These materials are composed of alternating layers of inorganic lead halide octahedra and organic ammonium cations. Most perovskite research studies so far have focused on organic sublattices based on phenethylammonium and alkylammonium cations, which are packed by van der Waals cohesive forces. Here, we report a more complex organic sublattice containing benzotriazole-based ammonium cations packed through interdigitated π-π stacking and hydrogen bonding. Single crystals and thin films of four perovskite derivatives are studied in depth with optical spectroscopy and X-ray diffraction, supported by density-functional theory calculations. We quantify the lattice stabilization of interdigitation, dipole-dipole interactions, and inter- as well as intramolecular hydrogen bonding. Furthermore, we investigate the driving force behind interdigitation by defining a steric occupancy factor σ and tuning the composition of the organic and inorganic sublattice. We relate the phenomenon of interdigitation to the available lattice space and to weakened hydrogen bonding to the inorganic octahedra. Finally, we find that the stabilizing interactions in the organic sublattice slightly improve the thermal stability of the perovskite. This work sheds light on the design rules and structure-property relationships of 2D layered hybrid perovskites.

Enhancing Organic–Inorganic Perovskite Thin Film Crystallization via Vapor–Solid Reaction by Modifying PbI2 Precursors Films with Pyridinium Trifluoromethanesulfonate

The vapor–solid reaction technique holds potential for producing large‐scale organic–inorganic perovskite films, using a two‐step deposition process. The sucess of perovskite formation heavily relies on the crystallization of lead iodide (PbI2) precursor films. However, the high crystallinity of PbI2 can hinder organic vapors' diffusion and negatively affecting the solar cells by increasing charge recombination and accelerating degradation. To address this, pyridinium trifluoromethanesulfonate (PTFS) is introduced into the PbI2 precursor solution to control the nucleation and growth of PbI2 films. PTFS has been found to effectively suppresses PbI2 crystallization and enhance the integration of formamidinium ion (FA+) through hydrogen bonding, facilitating the full transformation of PbI2 into perovskite. It also minimizes defect formation by interacting with uncoordinated Pb2+ and FA+ ions. These modifications have significantly enhanced power conversion efficiency (PCE), reaching up to 21.19%, and the devices have maintained 93% of their initial performance after 1580 h of exposure to air.

Crystal-chemical origins of the ultrahigh conductivity of metallic delafossites

Despite their highly anisotropic complex-oxidic nature, certain delafossite compounds (e.g., PdCoO2, PtCoO2) are the most conductive oxides known, for reasons that remain poorly understood. Their room-temperature conductivity can exceed that of Au, while their low-temperature electronic mean-free-paths reach an astonishing 20 μm. It is widely accepted that these materials must be ultrapure to achieve this, although the methods for their growth (which produce only small crystals) are not typically capable of such. Here, we report a different approach to PdCoO2 crystal growth, using chemical vapor transport methods to achieve order-of-magnitude gains in size, the highest structural qualities yet reported, and record residual resistivity ratios ( > 440). Nevertheless, detailed mass spectrometry measurements on these materials reveal that they are not ultrapure in a general sense, typically harboring 100s-of-parts-per-million impurity levels. Through quantitative crystal-chemical analyses, we resolve this apparent dichotomy, showing that the vast majority of impurities are forced to reside in the Co-O octahedral layers, leaving the conductive Pd sheets highly pure (∼1 ppm impurity concentrations). These purities are shown to be in quantitative agreement with measured residual resistivities. We thus conclude that a sublattice purification mechanism is essential to the ultrahigh low-temperature conductivity and mean-free-path of metallic delafossites.

Bright Excitonic Fine Structure in Metal-Halide Perovskites: From Two-Dimensional to Bulk.

The optical response of two-dimensional (2D) perovskites, often referred to as natural quantum wells, is primarily governed by excitons, whose properties can be readily tuned by adjusting the perovskite layer thickness. We have investigated the exciton fine structure splitting in the archetypal 2D perovskite (PEA)2(MA)n-1PbnI3n+1 with varying numbers of inorganic octahedral layers n = 1, 2, 3, and 4. We demonstrate that the in-plane excitonic states exhibit splitting and orthogonally oriented dipoles for all confinement regimes. The evolution of the exciton states in an external magnetic field provides further insights into the g-factors and diamagnetic coefficients. With increasing n, we observe a gradual evolution of the excitonic parameters characteristic of a 2D to three-dimensional transition. Our results provide valuable information concerning the evolution of the optoelectronic properties of 2D perovskites with the changing confinement strength.

High-pressure and high-temperature synthesis of crystalline Sb3 N5.

A chemical reaction between Sb and N2 was induced under high-pressure (32-35 GPa) and high-temperature (1600-2200 K) conditions, generated by a laser heated diamond anvil cell. The reaction product was identified by single crystal synchrotron X-ray diffraction at 35 GPa and room temperature as crystalline antimony nitride with Sb3 N5 stoichiometry and structure belonging to orthorhombic space group Cmc21 . Only Sb-N bonds are present in the covalent bonding framework, with two types of Sb atoms respectively forming SbN6 distorted octahedra and trigonal prisms and three types of N atoms forming NSb4 distorted tetrahedra and NSb3 trigonal pyramids. Taking into account two longer Sb-N distances, the SbN6 trigonal prisms can be depicted as SbN8 square antiprisms and the NSb3 trigonal pyramids as NSb4 distorted tetrahedra. The Sb3 N5 structure can be described as an ordered stacking in the bc plane of bi- layers of SbN6 octahedra alternated to monolayers of SbN6 trigonal prisms (SbN8 square antiprisms). The discovery of Sb3 N5 finally represents the long sought-after experimental evidence for Sb to form a crystalline nitride, providing new insights about fundamental aspects of pnictogens chemistry and opening new perspectives for the high-pressure chemistry of pnictogen nitrides and the synthesis of an entire class of new materials.

High‐pressure and high‐temperature synthesis of crystalline Sb3N5

AbstractA chemical reaction between Sb and N2 was induced under high‐pressure (32–35 GPa) and high‐temperature (1600–2200 K) conditions, generated by a laser heated diamond anvil cell. The reaction product was identified by single crystal synchrotron X‐ray diffraction at 35 GPa and room temperature as crystalline antimony nitride with Sb3N5 stoichiometry and structure belonging to orthorhombic space group Cmc21. Only Sb−N bonds are present in the covalent bonding framework, with two types of Sb atoms respectively forming SbN6 distorted octahedra and trigonal prisms and three types of N atoms forming NSb4 distorted tetrahedra and NSb3 trigonal pyramids. Taking into account two longer Sb−N distances, the SbN6 trigonal prisms can be depicted as SbN8 square antiprisms and the NSb3 trigonal pyramids as NSb4 distorted tetrahedra. The Sb3N5 structure can be described as an ordered stacking in the bc plane of bi‐ layers of SbN6 octahedra alternated to monolayers of SbN6 trigonal prisms (SbN8 square antiprisms). The discovery of Sb3N5 finally represents the long sought‐after experimental evidence for Sb to form a crystalline nitride, providing new insights about fundamental aspects of pnictogens chemistry and opening new perspectives for the high‐pressure chemistry of pnictogen nitrides and the synthesis of an entire class of new materials.

Metallic ruthenium ilmenites: First-principles study of MgRuO3 and CdRuO3

Ilmenites ABO3 provide a platform for electron correlation and magnetism on alternatively stacked honeycomb layers of edge-sharing AO6 or BO6 octahedra. When A and B are 3d transition metals, strong electron correlation makes the systems Mott insulators showing various magnetic properties, while when B is Ir with 5d electrons, competition between electron correlation and spin–orbit coupling realizes a spin–orbital coupled Mott insulator as a potential candidate for quantum spin liquids. Here, we theoretically investigate intermediate 4d ilmenites, ARuO3 with A = Mg and Cd, which have recently been synthesized and shown to be metallic, unlike the 3d and 5d cases. By using first-principles calculations, we optimize the lattice structures and obtain the electronic band structures. We show that MgRuO3 exhibits strong dimerization on RuO6 honeycomb layers, leading to the formation of bonding and anti-bonding bands for one of the three t2g orbitals; the lattice symmetry is lowered from R3̄ to P1̄, and the Fermi surfaces are composed of the other two t2g orbitals. In contrast, we find that CdRuO3 has a lattice structure close to R3̄, and all three t2g orbitals contribute almost equally to the Fermi surfaces. A comparison of our results with other Ru honeycomb materials, such as Li2RuO3, indicates that the metallic ruthenium ilmenites stand on a subtle balance among electron correlation, spin–orbit coupling, and electron–phonon coupling.

Kodamaite, Na3(Ca5Na)6Si16O36(OH)4F2·14−xH2O, x = ∼5, A New Layered Alkali-Alkaline Earth Fluorosilicate-Hydrate and Member of the Gyrolite Supergroup, from Mont Saint-Hilaire, Quebec, Canada: Description, Crystal-Chemical Considerations, and Genetic Implications

Abstract Kodamaite, ideally Na3(Ca5Na)6Si16O36(OH)4F2·14−xH2O, where x = ∼5, is a new mineral discovered at the Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada. It develops in spherulitic aggregates up to ∼2 mm across, comprising thin, platy to bladed crystals, with individual crystals averaging <0.05 × 0.5 mm. Crystals are dominated by the form pinacoid {100} with a lesser {hk0} form and typically range from tan to creamy-yellow to white in color, less often being colorless, light or dark green, or white. Associated minerals include eudialyte-group minerals, aegirine, a clinoamphibole, serandite-group minerals, natrolite, molybdenite, pyrite, fluorite, sodalite, catapleiite, rinkite-group minerals, albite, villiaumite, pyrochlore, fluorapatite, microcline, and erdite. Kodamaite is translucent to transparent and has a silky to slightly vitreous luster, a white streak, a Mohs hardness of ∼2, a perfect {001} cleavage, a sectile tenacity, and a smooth fracture. The mineral shows a pronounced bluish-white fluorescence under both long- and medium-wave ultraviolet radiation, much less so under short-wave radiation. The calculated density is 2.16 g/cm3. Optically, kodamaite is presumed to be optically biaxial, but its optical properties could not be readily discerned. An average nD = 1.507 (for λ = 590 nm) was calculated using data from the refined crystal structure. It is non-pleochroic, has low birefringence (first-order gray) and crystals are length slow and show no dispersion. The Raman spectrum shows two strong peaks at 607 (O–Si–O stretch) and 1070 cm−1 (Si–O stretch), along with several weaker ones over the range of ∼100–500 cm−1 arising from a combination of alkali–O bonds and lattice vibrations. An average of 11 energy-dispersive spectroscopic analyses gave Na2O 8.55, CaO 16.80, Fe2O3 0.39, SiO2 60.76, F 2.57, Cl 0.11, H2O (calc.) 12.49, O=F −1.08, O=Cl −0.02, total 100.98 wt.%. The empirical formula [based on Σ16(Si+S6+) cations apfu] is Na3.14(Ca4.72Na1.30Fe0.08)Σ6.00(Si15.92S6+0.08)Σ16O36.09(OH3.82F0.13Cl0.08)Σ4.00F2·9H2O. The crystal-structure formula is NaNa2Ca2Ca2(NaCa)2Si16O36(OH)4F2·14−xH2O with x = ∼5, which may be simplified to Na3(Ca5Na)6Si16O36(OH)4F2·9H2O. The mineral is triclinic, crystallizing in space group P, with a = 9.609(2), b = 9.630(2), c = 15.739(3) Å, α = 75.21(3), β = 85.22(3), γ = 60.12(3) °, V = 1219.3(1) Å3, Z = 1. The strongest six lines of the X-ray powder-diffraction pattern [dobs in Å (Iobs) (hkl)] are: 15.197 (100) (001), 3.833 (7) (004), 3.068 (7) (005), 2.996 (18) , 2.780 (14) , 1.831 (9) . The crystal structure was refined to R = 8.43%, wR2 = 23.50% using single-crystal X-ray diffraction data (1578 reflections with Fo > 4σFo). Kodamaite has a strongly layered crystal structure, with a motif based on single sheets of SiO4 tetrahedra (T) that are composed of regular, planar, six-membered rings (with a u6 arrangement; apices of the tetrahedra all point in a common direction, up = u). The regular rings of tetrahedra are linked in the (001) plane by SiO3(OH) tetrahedra, whose apical directions are opposite to those in the ring (down; d). Linkages between the two types of tetrahedra give rise to an irregular, six-membered ring of tetrahedra with a u2du2d arrangement. The combination of regular and irregular six-membered rings of tetrahedra produces a three-connected (63)4 net. Two symmetry-related T layers, designated T2 and −T2, sandwich a closest-packed layer of edge-sharing Naφ6 and Caφ6 octahedra and Naφ8 polyhedra (φ = undefined ligand; O, F), forming a quasi-layer of octahedra (O). Refinement of the crystal structure shows the Ca sites are dominated by Ca with small amounts of Na (9:1 ratio); one of the sites has an equal concentration of Ca and Na, suggesting ordering of the two in a single site. The arrangement of T and O layers produces a TOT module with the interlayer space being occupied by H2O groups. Charge-balance arguments and observed anion–anion distances support ordering of F in a single, distinct site. The complete crystal structure of kodamaite conforms to a scheme, which is similar to that of the closely related minerals martinite and ellingsenite. All are classed in the gyrolite supergroup, which includes minerals in five groups, all having similar but distinct crystal-structure features. The crystal-chemical relationships among the groups and implications in terms of the stacking of various modules are presented and discussed. Kodamaite is a late-stage mineral that developed under hydrothermal conditions at T < 200 °C, most likely under high to very high alkalinity. The interaction of these fluids with pre-existing minerals, including pectolite, eudialyte-group minerals, and sodalite, is likely essential to the formation of the kodamaite.

(Invited) Clay: A Ubiquitous Sustainable Material for Energy Applications

Silicates and their precursors make up the majority of the land mass on Earth in the form of inorganic components of soil, silt, and sediment. Clay minerals, essentially hydrous silicates or aluminosilicates, are widely used in a variety of applications and industries, including ceramic goods, cement, drilling fluids, molding sands, anti-corrosion paints, paper manufacturing process, water treatment, polymer-clay composites for automotive industries, and even in medicine and pharmaceutical applications. Lately, it has found use in developing cost-effective ink, drug delivery, food packaging using oxygen barrier properties, and battery separators.Structure-property features of clays reveal that one can functionalize clays leveraging their porous structures, tunable surface areas, remarkable thermal and mechanical stabilities, and abundant reserves, which make clay one of the cheapest natural materials from a sustainable source and one of the most sought-after materials for a variety of applications. Clays generally have layered structures with the possibility of interchangeable intercalated ions and tunable chemical properties. They are composed of alternating tetrahedral silica (T) and octahedral alumina (O) sheets arranged in a 1:1 ratio (T-O). The tetrahedral sheets are formed from Si4+ ions coordinated with oxygen; however, the Al3+ metal ion is the central atom in the octahedral sheet. Bentonite or Montmorillonite is one of the most used clay minerals owing to its abundance and low cost. Notably, naturally occurring Bentonite has some octahedral sites occupied by the Mg2+ and Fe2+ ions. The presence of these ions allows tuning chemical properties and mechanical strength by functionalizing with organic molecules within the octahedral layers. Over the decades, polymer-based clay composites have been developed using this technique. Herein, we shed light on a new strategy to create hybrid clay films made from small organic molecules with charges at two ends, known as zwitter ions. Using this novel approach, we have developed cost-effective, environmentally benign, and biocompatible clay films with unique physical and chemical properties, where the clay galleries are infused with intercalating zwitter ions. The insertion of these ions increases the interlayer spacing while simultaneously allowing the formation of mechanically robust and thermally and chemically durable clay films. These hybrid clay films can be used as membranes and have been characterized using powder X-ray diffraction, X-ray photoelectron spectra, rheology, ATR-IR spectra, DSC-TGA, dynamic mechanical analyses, and imaging techniques. The effect of varying the carbon chain length and changing functional groups in these zwitter ion species has been verified to significantly impact the clay slurry's rheology and control the clay films' interlayer spacing. Electrochemical impedance spectroscopy studies of the hybrid films confirm that intercalation of zwitter ions in the clay structures leads to improved ionic conductivity of the clays. A series of impedance spectroscopy experiments conducted using various electrolytes reveal remarkable improvements in the ionic conductivity of the hybrid clay films. Contrary to metal ion batteries due to dendritic growth causing thermal degradation of the batteries, the hybrid clay films possess high thermal and mechanical stability that makes them versatile for energy materials. A cost-effective solution to engineering such hybrid films provides an efficient and recycle-free avenue to develop a new generation of materials from sustainable sources for energy applications, especially for battery separators and capacitors for the future.

Tuning the Composition, Crystal Structure and Morphology of Manganese(III/IV) Oxide for High-Power Storage Applications

If inherently intermittent renewable energy technologies are to offer a practical alternative to conventional heat engines, it is critically important that efficient, cost-effective and sustainable energy storage solutions are developed to decouple supply and demand profiles. A promising strategy is to pair the competitive energy densities of batteries with the superior cycling lifetimes and power densities of supercapacitors,[1] employing an appropriate maximum power point tracking (MPPT) system to optimise energy exchange between these complementary devices.[2] Mixed-valence manganese(III/IV) oxides (MnOz, where z ranges between 1.5 and 2.0) have emerged as foremost candidates for the electroactive material in supercapacitor cathodes due to their low toxicity, minimal cost,[3] ready availability (manganese appears at an average concentration of ca. 1,000 ppm in the Earth’s crust[4]), wide electrochemical stability window (ca. 1.0 V in aqueous electrolytes[5]), and high maximum theoretical specific capacitance (ca. 1,370 F g-1, based on the reduction of Mn4+ ions by a single electron[6]). Charge storage in MnOz is predominantly mediated by the pseudocapacitive intercalation of cations from the surrounding electrolyte in each discharge phase, followed by the release of these guest ions during charging.Of the various crystallographic phases of MnOz, cryptomelane (α-MnOz) and birnessite (δ-MnOz) polymorphs are deemed two of the most promising candidates for storage applications because they possess characteristically wide channels for intercalation/de-intercalation:[8,9] α-MnOz consists of ca. 4.6 Å diameter one-dimensional tunnels enclosed between corner-sharing MnO6 octahedra, whereas δ-MnOz comprises two-dimensional layers of MnO6 octahedra separated by ca. 7.0 Å. Herein, a scalable, low-cost synthesis procedure is discussed that enables the production of highly pseudocapacitive birnessite and cryptomelane electrodes with tuneable material characteristics, including particle morphology, crystallographic structure, average Mn oxidation state, and the level of pre-intercalation by Na+ and K+ ions.[10] In addition to comparing the electrochemical properties of these NaxKyMnOz products in aqueous conditions, their application within an asymmetric supercapacitor is showcased: by optimising the relative masses of a NaxKyMnOz cathode and activated carbon anode in a 100 cm2 aqueous full-cell configuration, discharge capacitances in the range 10-30 F g-1 can be achieved over a voltage span of 1.8 V at current densities as high as 10 A g-1, with Coulombic efficiency exceeding 80% up to ca. 20 A g-1. With these competitive performance characteristics, the developed NaxKyMnOz materials are a promising option for high-power supercapacitor cathodes, helping to pave the way towards more efficient and sustainable energy storage.

Surface Reconstruction of a Perovskite Film by an Organic Salt for High-Performance Solar Cells with Improved Stability.

Organic-inorganic lead halide perovskites have undergone tremendous development due to their excellent optoelectrical properties, achieving exceptional photovoltaic performance up to over 25%. The interface engineering method has a significant role in further improving the perovskite solar cell performance to its limit. Herein, we fabricated a modified GA0.07MA0.93PbI3 perovskite film using the organic amine small molecule 3-(aminomethyl)pyridine (3AP), which increased the grain sizes and crystallinity through the modulated melting process as well as reacted with the surface component, especially the defect site of the PbI6 octahedral layer, resulting in a high-quality perovskite film. The perovskite films without (pristine) and with toluene were also fabricated to prove the significant role of the 3AP organic molecule. The 3AP-modified GA0.07MA0.93PbI3 perovskite film exhibits a long carrier lifetime and suppresses the charge recombination loss, resulting in an increased fill factor (FF) of 75.66% and a power conversion efficiency (PCE) of 17.28%, which are higher than those of pristine (FF, 66.36%; PCE, 14.06%) and toluene-treated perovskite devices (FF, 72.40%; PCE, 16.84%). More importantly, the 3AP-modified perovskite device shows remarkable environmental stability to the ambient conditions, with the PCE retaining 92% of the initial PCE for over 1000 h under ambient conditions.

Speciation studies at the Illite - solution interface: Part 1 – Sorption of phosphate ions

Although phosphate ion (hereafter “P”) sorption is known to influence clay surface reactivity and trace metal behavior in the environment, there is still a lack of in situ spectroscopic evidence on the identity of phosphate sorption species formed at the interface between solution and clays with a 2:1 layered structure (2 silica tetrahedral: 1 octahedral layers), which are ubiquitous in soils and clay formations. We studied the surface speciation of phosphate ions by in situ spectroscopic monitoring along P sorption at the interface between a solution and a homoionic Na-illite, as a function of time or aqueous phosphate concentration (20–250 µM) leading to low/moderate P surface coverage. We also combined them with batch sorption experiments and electrophoretic mobility (EM) measurements. Macroscopic data indicated that the percentage of P sorption depends on pH, aqueous phosphate concentration, and the clay/solution ratio of the experiment, i.e., the coverage of the clay surface by P, with a maximal sorption capacity of the clay equal to ca. 6 µmol.g−1 at pH 4. Macroscopic and EM data further suggest that P sorption mechanisms onto illite confer negative charges on the surface and involve several sorption species and/or surface sites present on the clay edges. In situ FTIR spectra showed that, at acidic pH, three types of phosphate surface species exist at the illite-solution interface: an outer-sphere surface complex (OSSC) of phosphate (ΞSOH2+…H2PO4-, with S referring to a sorption site on the clay), an inner-sphere surface complex (ISSC) of phosphate, probably a monodentate binuclear surface complex ((ΞSO)2PO2) formed by surface ligand exchange with high-affinity aluminol sites and, to a lesser extent, low-affinity sites on the clay edges, and, in limited amounts, an Al-phosphate surface precipitate. Phosphate ion sorption occurs through the initial formation of the OSSC of phosphate, which dominates phosphate surface speciation at short reaction times and low P concentrations and transforms over time into the ISSC of phosphate. This study presents the first published in situ surface speciation of phosphate ions sorbed at the interface between a solution and an illite. The evidence of a strong sorption of phosphate ions at this clay surface provides new and sound knowledge to better understand the environmental fate of phosphate ions and trace metals, particularly in agricultural soil - groundwater continua or in clay host rocks considered for high-level radioactive waste disposal.

Lizardite–h-BN heterostructures—Application of clay minerals in technology

Graphene has been a subject of great interest not only due to its fascinating properties but also for being the pioneer among 2D van der Waals (vdW) materials. Hexagonal boron nitride, an isomorph of graphene and a wide gap insulator, is commonly referred to as white graphene. The combination of the insulating hexagonal boron nitride (h-BN) with other crystals to form heterostructures provide a path for engineering and manipulating new physics and device properties. In this work, we investigate the vdW heterostructures formed by assembling h-BN and lizardite, a clay-mineral that is abundant in nature and represents the most stable polymorph of the serpentine family. The optoelectronic properties of three distinct heterostructures are presented to discern the characteristics of the systems. We observe that unlike lizardite and h-BN which are insulators, all the three heterostructures exhibit a semiconducting nature. The direct gap of the heterostructure in which two h-BN sheets are simultaneously placed above and below the octahedral and tetrahedral layers also makes it relevant for optoelectronic devices. Additionally, unlike lizardite, the heterostructures demonstrate a polarization-dependent optical properties. The study of the assembled structures combining the clay-mineral with h-BN not only widens the spectrum of vdW heterostructures but also explores their potential within the context of the serpentine family.

Nanoplatelet Superlattices by Tin-Induced Transformation of FAPbI3 Nanocrystals.

The transition from 3D to 2D lead halide perovskites is traditionally led by the lattice incorporation of bulky organic cations. However, the transformation into a coveted 2D superlattice-like structure by cationic substitution at the Pb2+ site of 3D perovskite is unfamiliar. It is demonstrated that the gradual increment of [Sn2+ ] alters the FASnx Pb1- x I3 nanocrystals into the Ruddlesden-Popper-like nanoplatelets (NPLs), with surface-absorbed oleic acid (OA) and oleylamine (OAm) spacer ligand at 80°C (FA+ : formamidinium cation). These NPLs are stacked either by a perfect alignment to form the superlattice or by offsetting the NPL edges because of their lateral displacements. The phase transition occurs from the Sn/Pb ratio ≥0.011, with 0.64 wt% of Sn2+ species. At and above Sn/Pb = 0.022, the NPL superlattice stacks start to grow along [00l] with a repeating length of 4.37(3) nm, comprising the organic bilayer and the inorganic block having two octahedral layers (n = 2). Besides, a photoluminescence quantum yield of 98.4% is obtained with Sn/Pb = 0.011 (n ≥ 4), after surface passivation by trioctylphosphine (TOP).

Regulating Phase Distribution of Dion-Jacobson Perovskite Colloidal Multiple Quantum Wells Toward Highly Stable Deep-Blue Emission.

Metal halide perovskite colloidal quantum wells (CQWs) hold great promise for modern photonics and optoelectronics. However, current studies focus on Ruddlesden-Popper (R-P) phase perovskite CQWs that contain bilayers of monovalent long-chain alkylamomoniums between the separated perovskite octahedra layers. The bilayers are packed back-to-back via weak van der Waals interaction, resulting in inferior charge carrier transport and easier decomposition of perovskite. This report first creates a new type of perovskite colloidal multiple QWs (CMQWs) in the form of Dion-Jacobson (D-J) structure by introducing an asymmetric diammonium cation. Furthermore, the phase distribution is optimized by the synergistic effect of valeric acid and zwitterionic lecithin, finally achieving pure deep-blue emission at 435nm with narrow full width at half maximum. The diammonium layer in D-J perovskite CMQWs features extremely short width of only ≈0.6nm, thereby contributing to more effective charge carrier transport and higher stability. Through the continuous photoluminescence (PL) measurement and corresponding theoretical calculation, the higher stability of D-J perovskite CMQWs than that of R-P structural CMQWs is confirmed. This work reveals the inherent superior stability of D-J structural CMQWs, which opens a new direction for fabricating stable perovskite optoelectronics.

Cation exchange route to a Eu(II)-containing tantalum oxide

Traditional synthetic efforts to prepare Eu(II)-containing oxides have principally involved the use of high temperature reactions starting from EuO or a controlled, highly-reducing, atmosphere. Conversely, chimie douce approaches that are more amenable to the targeted syntheses of new, and potentially metastable, Eu(II)-oxides have yet to be explored. Herein, a cation-exchange route to new Eu(II)-containing oxides, e.g., EuTa4-xO11 (x = 0.04), has been discovered and its structure determined by powder X-ray diffraction (Space group P6322 (#182), a = 6.2539(2) Å; c = 12.3417(2) Å). The compound derives from the cation exchange of Na2Ta4O11, via a reaction with EuBr2 at 1173 K, and replacement by half the number of divalent Eu cations. Rietveld refinements show preferential ordering of the Eu cations over one of the two possible cation sites, i.e., Wyckoff site 2d (∼94%; Eu1) versus 2b (∼6%; Eu2). Total energy calculations confirm an energetic preference of the Eu cation in the 2d site. Tantalum vacancies of ∼1% occur within the layer of Eu cations and TaO6 octahedra, and ∼20% partial oxidation of Eu(II) to Eu(III) cations from charge balance considerations. 151Eu Mössbauer spectroscopy measured at 78 K found a Eu(II):Eu(III) ratio of 69:31, with a relatively broad line width of the former signal of Γ = 7.6(2) mm s–1. Also, the temperature-dependent magnetic susceptibility could be fitted to a Curie Weiss expression, giving a μeff = 6.2 μB and θCW = −10 K and confirming a mixture of Eu(II)/Eu(III) cations. The optical bandgap of EuTa4-xO11 was found to be ∼1.5 eV (indirect), significantly redshifted as compared to ∼4.1 eV for Na2Ta4O11. Spin-polarized electronic structure calculations show that this redshift stems from the addition of Eu 4f7 states as a higher-energy valence band. Thus, these results demonstrate a new cation-exchange approach that represents a useful synthetic pathway to new Eu(II)-containing oxides for tunable magnetic and optical properties.

Layer control of Sr1.8Bi0.2Nan-3NbnO3n+1 (n = 3–5) perovskite nanosheets: dielectric to ferroelectric transition of film deposited by Langmuir Blodgett method

Solution-based processable high-k 2-dimensional (2D) ferroelectrics have attracted significant interest for use in next-generation nanoelectronics. Although few studies on potential 2D ferroelectric nanosheets in local areas have been conducted, reports on the thin-film characteristics applicable to the device are insufficient. In this study, we successfully synthesize high-k 2D Sr1.8Bi0.2Nan-3NbnO3n+1 (octahedral units, n = 3–5) nanosheets by the engineering of the n of NbO6 octahedral layers with A-site modification, and realized ferroelectric characteristics in ultrathin films (below 10 nm). The nanosheets are synthesized by a solution-based cation exchange process and deposited using the Langmuir-Blodgett (LB) method. As increasing the NbO6 octahedral layer, the thickness of the nanosheets increased and the band gaps are tuned to 3.80 eV (n = 3), 3.76 eV (n = 4), and 3.70 eV (n = 5). In addition, the dielectric permittivity of the 5-layer stacked nanofilm increase to 26 (n = 3), 33 (n = 4), and 62 (n = 5). In particular, the increased perovskite layer exhibits large distortions due to the size mismatch of Sr/Bi/Na ions at the A-site and promotes local ferroelectric instability due to its spontaneous polarization along the c-axis caused by an odd n number. We investigate the stable ferroelectricity in Pt/ 5-layer Sr1.8Bi0.2Na2Nb5O16 / Nb:STO capacitor by polarization-electric field (P-E) hysteresis; the coercive electric field (Ec) was 338 kV cm−1 and the remnant polarization (Pr) 2.36 μC cm−2. The ferroelectric properties of ultrathin 2D materials could drive interesting innovations in next-generation electronics.