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The synthesis and characterizations of sandwich structured layered materials through direct combination of oppositely charged building blocks, such as positively charged layered double hydroxide (LDH) nanosheets and negatively charged oxide nanosheets, are presented. The characterization has shown the layered structures fabricated via layer-by-layer self-assembly, in which LDH nanosheets and oxide sheets are alternately stacked.

A topochemical synthetic approach is described for transforming brucite-like [Co.sup.2+] -[Fe.sup.2+] into hydrotalcite-like C[o.sup.2+] -F[e.sup.3+] layered double hydroxides (LDHs) is described. The results have shown that after a normal ion-exchange process, [Co.sup.2+] -[Fe.sup.3+] LDHs accommodating perchlorate anions are exfoliated into unilamellar nanosheets in formamide by an ultrasonic treatment.

Photoinduced hydrophilic conversion properties of titania nanosheets were investigated. The hydrophilic conversion rate (k) for the monolayer film of titania nanosheets was proportional to the intensity (I) of irradiated light, suggesting that the hydrophilic conversion of titania nanosheet surface proceeded under light-limited conditions even with a high concentration of photoexcited carriers.

Inorganic multilayer films and hollow shells with pillared architectures are fabricated layer-by-layer on spherical poly(methyl methacrylate) (PMMA) templates as well as flat substrates through the electrostatic self-assembly technique. Positively charged polyoxocations of aluminum Keggin ions are employed both as inorganic binder and as pillaring agent in electrostatic self-assembly with exfoliated unilamellar crystallites of Ti(sub 0.91)O2, which yielded new types of ultrathin films and core-shell composites.

The thermal and photochemical reactions of 1,2-bis(diazoketone)s through their Wolff rearrangements produces high and low yields of several 2-cyclopenten-1-one derivatives, respectively, with complete stereospecificity. This method also produces the first conventionally synthesized trans-hydro-indenones without substituents at the ring juncture, a structure confirmed by X-ray analysis as well as 1H NMR spectroscopy. Alpha-diazoketones are made more useful through these synthesis reactions.

A structural transformation of the Li[Mn.sub.2][O.sub.4] spinel is reported, by which the spinel structure is found to transform under high pressure of 6GPa, during heating at 1100 degrees Celsius or above. The compound is identified to be the polycrystalline Ca[Fe.sub.2][O.sub.4] (calcium ferrite) type, is 6% denser than the spinel, and exhibits semiconducting-like characteristics above 5 K.

Fluorescent composite materials of exfoliated titania nanosheets, [Ti.sub.0.91][O.sub.2] and rare earth (RE) complexes, Eu([phen.sub.2])[Cl.sub.3]*2[H.sub.2]O and Tb([phen.sub.2])[Cl.sub.3]*2[H.sub.2]O (phen = 1,10-phenanthroline), are synthesized via flocculation between them. The results show that the incorporation of a rare earth emissive complex into a layered inorganic host material is a useful strategy to improve its thermal stability and emission efficiency.

The controlled synthesis of single-crystal platelets of alpha- and beta-Co(OH)2 via homogeneous precipitation using hexamethylenetetramine as a hydrolysis agent is reported. Polarized optical microscope observations revealed clear liquid crystallinity of colloidal suspensions of the high aspect-ratio platelets.

Unilamellar nanosheet crystallites of manganese oxide generated the anodic photocurrent under visible light irradiation while the nanosheets themselves were stable and UV-visible absorption spectra. The monolayer film of MnO2 nanosheets exhibit the incident photon to electron conversion efficiency of 0.16% in response to the monochromatic light irradiation, which is comparable to those for sensitization of monolayers dyes adsorbed on a flat single-crystal surface.

The electrochemical and photoelectrochemical properties of the titania nanosheets are explored to understand their electronic band structure.

Strong demand for solid-state lithiumbatteries has prompted intensive research for achieving fast ionicconduction in solids. Although the highest conductivity found amongsulfides is higher than that of liquid electrolytes, it improves thebattery performance only in combination with electrodes via a low-resistanceinterface. This Article reviews some interfacial structures that lowerthe interfacial resistance to enable high-power interfaces by controllingthe carrier density. [ABSTRACT FROM AUTHOR]

Crystal structures of sodium cobalt oxide bilayer-hydrates were analyzed on the basis of superstructure models by assuming that the host and guest layers are commensurate. The superstructure model gave better fitting results compared to the incommensurate composite crystal model, suggesting that the host and guest layers are commensurate and have a 2 × 2 superstructure. Although the Co−O bonds in the superconductive CoO2layers were reported to be shorter than that was expected from the Co oxidation states, the bond lengths refined in this study were consistent with the oxidation states. [ABSTRACT FROM AUTHOR]

This paper describes a topochemical synthetic approach to Co2+Fe3+ layered double hydroxides (LDHs). Micrometer-sized hexagonal platelets of brucite-like Co2/3Fe1/3(OH)2 were first prepared by a homogeneous precipitation of an aqueous solution of divalent cobalt and ferrous ions through hexamethylenetetramine (HMT) hydrolysis under a nitrogen gas atmosphere. A subsequent oxidative intercalation process, by the action of iodine (l2) in chloroform (CHCl3), transformed the precursory brucite-like Co2+ Fe2+ hydroxides into hydrotalcite-like Co2+ Fe3+ LDHs, in which the oxidization of Fe2+ into Fe3+ induced positive charges to the octahedral hydroxyl layers while anions (1) were intercalated into the interlayer space. Co2+ Fe3+ LDHS inherited the high crystallinity and hexagonal platelet morphology from their brucite-like precursor due to the topotactic nature of the transformation, which was verified by abundant microscopic and spectroscopic characterizations. After a normal ion-exchange process, Co2+ Fe2+ LDHs accommodating perchlorate anions were exfoliated into unilamellar nanosheets in formamide by an ultrasonic treatment. [ABSTRACT FROM AUTHOR]

Exfoliated oxide nanosheets such as Ti0.91O2 and Ca2Nb3O10 and layered double hydroxide (LDH) nanosheets of Mg2/3A∣1/3(OH)2 were restacked into inorganic sandwich layered materials. Sequential adsorption of these oppositely charged nanosheets from their colloidal suspensions yielded multilayer ultrathin films while their simple mixing produced lamellar flocculates. Eliminating carbonate ions from the reaction system was found to be essential for successfully achieving the sandwich structures. The flocculated materials as well as the films were characterized by atomic force microscopy (AFM), UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and chemical analysis, which all supported the formation of the ordered sandwich structures. AFM observations revealed alternate dense tiling of LDH nanosheets and oxide nanosheets onto a substrate surface. UV-visible absorption spectra exhibited progressive enhancement of optical density due to oxide nanosheets as a function of deposition cycles, providing strong evidence for regular growth of multilayer films. The combinations of Mg2/3Al1/3(OH)2/Ti0.91O2 and Mg1/3Al1/3(OH)2/Ca2Nb3O10 produced XRD Bragg peaks having multilayer spacings of 1.2 and 2.0 nm, respectively. These basal spacing values are compatible with the sum of thickness of LDH nanosheets and corresponding oxide nanosheets. TEM images of flocculated samples displayed lamellar features with two different constituent layers appearing alternately. [ABSTRACT FROM AUTHOR]

A new form of LiMn2O4 is reported. The structure is the CaFe2O4-type and 6% denser than the spinel. The structure transformation was achieved by heating at 6 GPa. Analysis of the neutron diffraction pattern confirmed an average of the structure; the unit cell was orthorhombic at a = 8.8336(5) Å, b = 2.83387(18) Å, and c = 10.6535(7) Å (Pnma). Electron diffraction patterns indicated an order of superstructure 3a × b × c, which might be initiated by Li vacancies. The exact composition is estimated at Li0,92Mn2O4 from the structure analysis and quantity of intercalated Li. The polycrystalline CaFe2O4-type compound showed semiconducting-like characters over the studied range above 5 K. The activation energy was reduced to ∼0.27 eV from ∼0.40 eV at the spinel form, suggesting a possible enhancement of hopping mobility. Magnetic and specific-heat data indicated a magnetically glassy transition at ∼10 K. As the CaFe2O4-type transition was observed for the mineral MgAl2O4, hence the new form of the lithium manganese oxide would provide valuable opportunities to study not only the magnetism of strongly correlated electrons but also the thermodynamics of the phase transition in the mantle. [ABSTRACT FROM AUTHOR]

This paper describes a systematic study on the synthesis, anion exchange, and delamination of Co-Al layered double hydroxide (LDH), with the aim of achieving fabrication and clarifying the properties of LDH nanosheet/polyanion composite films. Co-Al-CO3 LDH hexagonal platelets of 4 μm in lateral size were synthesized by the urea method under optimized reaction conditions. The as-prepared CO32--LDH was converted to Cl--LDH by treating with a NaCl-HCl mixed solution, retaining its high crystallinity and hexagonal platelike morphology. LDHs intercalated with a variety of anions (such as NO3-, ClO4-, acetate, lactate, dodecyl sulfate, and oleate) were further prepared from Cl--LDH via an anion-exchange process employing corresponding salts. Exchanged products in various anion forms were found to show different delamination behaviors in formamide. Among them, best results were observed for NO3--LDH in terms of the exfoliating degree and the quality of the exfoliated nanosheets. The delamination gave a pink transparent suspension containing well-defined nanosheets with lateral sizes of up to 2 μm. The resulting nanosheets were assembled layer-by-layer with an anionic polymer, poly(sodium styrene 4-sulfonate) (PSS), onto quartz glass substrates to produce composite films. Magnetic circular dichroism (MCD) measurements revealed that the assembled multilayer films exhibited an interesting magneto-optical response. [ABSTRACT FROM AUTHOR]

We report on the controlled synthesis of single-crystal platelets of α- and β-Co(OH)2 via homogeneous precipitation using hexamethylenetetramine as a hydrolysis agent. The α- and β-Co(OH)2 hexagonal platelets of several micrometers in width and about 15 nm in thickness were reproducibly yielded in rather dilute CoCl2 solutions in the presence and absence of NaCI at 90 °C, respectively. The phase and size control of the products were achieved by varying both CoCl2 and NaCI concentrations. Polarized optical microscope observations revealed clear liquid crystallinity of colloidal suspensions of these high aspect-ratio platelets. The as-prepared α-Co(OH)2 containing interlayer chloride ions was intercalated with various inorganic or organic anions, keeping its high crystallinity and hexagonal platelike morphology. [ABSTRACT FROM AUTHOR]

This paper reports the thin-film synthesis of Li 3 PO 4 solid electrolytes by RF magnetron sputtering. A relatively high ionic conductivity of more than 1 × 10 -6 S cm -1 is achieved. It is revealed that the crystallization of Li 3 PO 4 impedes ionic conduction, and a moderate amount of O 2 addition to Ar suppresses the crystallization and guarantees long-term deposition. Another important finding in this study is that when Li 3 PO 4 is deposited on a LiCoO 2 film to construct a thin-film battery, the LiCoO 2 film can be damaged depending on the substrate bias potential relative to the cathode potential propagated through the sputtering plasma. Active control of the bias potential to avoid the damage realizes negligible interface resistance in the thin-film battery., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)

Size-induced suppression of permittivity in perovskite thin films is a fundamental problem that has remained unresolved for decades. This size-effect issue becomes increasingly important due to the integration of perovskite nanofilms into high-κ capacitors, as well as concerns that intrinsic size effects may limit their device performance. Here, we report a new approach to produce robust high-κ nanodielectrics using perovskite nanosheet (Ca2Nb3O10), a new class of nanomaterials that is derived from layered compounds by exfoliation. By a solution-based bottom-up approach using perovskite nanosheets, we have successfully fabricated multilayer nanofilms directly on SrRuO3 or Pt substrates without any interfacial dead layers. These nanofilms exhibit high dielectric constant (>200), the largest value seen so far in perovskite films with a thickness down to 10 nm. Furthermore, the superior high-κ properties are a size-effect-free characteristic with low leakage current density (<10(-7) A cm(-2)). Our work provides a key for understanding the size effect and also represents a step toward a bottom-up paradigm for future high-κ devices.

Layered cesium tungstate, Cs(6+x)W(11)O(36), with two-dimensional (2D) pyrochlore structure was exfoliated into colloidal unilamellar sheets through a soft-chemical process. Interlayer Cs ions were replaced with protons by acid exchange, and quaternary ammonium ions were subsequently intercalated under optimized conditions. X-ray diffraction (XRD) measurements on gluelike sediment recovered from the colloidal suspension by centrifugation showed a broad pattern of a pronounced wavy profile, which closely matched the square of calculated structure factor for the single host layer. This indicates the total delamination of the layered tungstate into nanosheets of Cs(4)W(11)O(36)(2-). Microscopic observations by transmission electron microscopy and atomic force microscopy clearly revealed the formation of unilamellar crystallites with a very high 2D anisotropy, a thickness of only approximately 2 nm versus lateral size up to several micrometers. In-plane XRD analysis confirmed that the 2D pyrochlore structure was retained. The colloidal cesium tungstate nanosheet showed strong absorption of UV light with sharp onset, suggesting a semiconducting nature. Analysis of the absorption profile provided 3.6 eV as indirect band gap energy, which is 0.8 eV larger than that of the bulk layered precursor, probably due to size quantization. The nanosheet exhibited highly efficient photochromic properties, showing reversible color change upon UV irradiation.

In this paper, we describe a general process for the synthesis and delamination of a family of highly crystalline Al-based and transition-metal-bearing layered double hydroxides (LDHs). Large-sized and monodispersed hexagonal platelike particles of binary-component M(II)-Al-CO3 and ternary-component M(II)-M'(II)-Al-CO3 LDHs (M(II) and M'(II) = Fe, Co, Ni, or Zn) were prepared at first by the urea method under optimized conditions. These CO32--LDHs were converted into other monovalent-anion-containing LDHs by means of a salt-acid treatment and subsequent anion-exchange processes. Finally, well-defined LDH nanosheets were obtained by delamination of NO3--LDHs in formamide.

Fluorescent composite materials of exfoliated titania nanosheets, Ti(0.91)O(2), and rare earth (RE) complexes, Eu(phen)(2)Cl(3).2H(2)O and Tb(phen)(2)Cl(3).2H(2)O (phen = 1,10-phenanthroline), were synthesized via flocculation between them. X-ray diffraction measurements and transmission electron microscopy observations confirmed a restacked lamellar structure for the composites, and elemental analysis revealed a high RE complex content of 15 wt %. The decomposition temperature of the complexes trapped in the composites was improved to 420 degrees C from 250 degrees C for the free form. The restacked composite composed of Ti(0.91)O(2) nanosheets and Eu(phen)(2) exhibited characteristic red emission from the complex, while the composite with Tb(phen)(2) gave featureless emission originated from the ligand. This phenomenon can be explained by a shift of triplet state level of the ligand after encapsulation in the host titania nanosheets. The quantum yield of europium complex in the composite was enhanced 1.6 times more than that of the pure complex.

We report a Rietveld refinement analysis and X-ray absorption study on a green-color Cl(-)-intercalated alpha-type cobalt hydroxide phase. The refinement clearly demonstrated that one-fifth to one-sixth of the Co(II) at octahedral sites was replaced by pairs of tetrahedrally coordinated Co(II) on each side of the hydroxide plane, represented by a structural formula of [Co(octa)(0.828)Co(tetra)(0.348)(OH)2](0.348+)Cl(0.348).0.456H2O. X-ray absorption spectroscopy also indicated that the divalent cobalt were in local neighboring environments of both octahedral and tetrahedral coordination. Furthermore, UV-vis spectroscopic measurements elucidate the typical green/blue color of an alpha-type cobalt hydroxide.