A wide variety of cation-exchangeable layered transition metal oxides and their relatively rare counterparts, anion-exchangeable layered hydroxides, have been exfoliated into individual host layers, i.e., nanosheets. Exfoliation is generally achieved via a high degree of swelling, typically driven either by intercalation of bulky organic ions (quaternary ammonium cations, propylammonium cations, etc.) for the layered oxides or by solvation with organic solvents (formamide, butanol, etc.) for the hydroxides. Ultimate two-dimensional (2D) anisotropy for the nanosheets, with thickness of around one nanometer versus lateral size ranging from submicrometer to several tens of micrometers, allows them to serve either as an ideal quantum system for fundamental study or as a basic building block for functional assembly. The charge-bearing inorganic macromolecule-like nanosheets can be assembled or organized through various solution-based processing techniques (e.g., flocculation, electrostatic sequential deposition, or the Langmuir-Blodgett method) to produce a range of nanocomposites, multilayer nanofilms, and core-shell nanoarchitectures, which have great potential for electronic, magnetic, optical, photochemical, and catalytic applications.

Nanosheets of oxides and hydroxides: Ultimate 2D charge-bearing functional crystallites.

The Binary Rare Earth Oxides.

The magnetic, optical, and transport properties of representatives of a class of magnetic semiconductors: The europium chalcogenides

A comprehensive review of the thermodynamic properties of the oxide compounds of the lanthanide and actinide elements is presented. The available literature data for the solid, liquid, and gaseous state have been analysed and recommended values are presented. In case experimental data are missing, estimates have been made based on the trends in the two series, which are extensively discussed.

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The Thermodynamic Properties of the f-Elements and their Compounds. Part 2. The Lanthanide and Actinide Oxides

The synthesis process and crystal structure evolution for a family of stoichiometric layered rare-earth hydroxides with general formula Ln(8)(OH)(20)Cl(4) x nH(2)O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y; n approximately 6-7) are described. Synthesis was accomplished through homogeneous precipitation of LnCl(3) x xH(2)O with hexamethylenetetramine to yield a single-phase product for Sm-Er and Y. Some minor coexisting phases were observed for Nd(3+) and Tm(3+), indicating a size limit for this layered series. Light lanthanides (Nd, Sm, Eu) crystallized into rectangular platelets, whereas platelets of heavy lanthanides from Gd tended to be of quasi-hexagonal morphology. Rietveld profile analysis revealed that all phases were isostructural in an orthorhombic layered structure featuring a positively charged layer, [Ln(8)(OH)(20)(H(2)O)(n)](4+), and interlayer charge-balancing Cl(-) ions. In-plane lattice parameters a and b decreased nearly linearly with a decrease in the rare-earth cation size. The interlamellar distance, c, was almost constant (approximately 8.70 A) for rare-earth elements Nd(3+), Sm(3+), and Eu(3+), but it suddenly decreased to approximately 8.45 A for Tb(3+), Dy(3+), Ho(3+), and Er(3+), which can be ascribed to two different degrees of hydration. Nd(3+) typically adopted a phase with high hydration, whereas a low-hydration phase was preferred for Tb(3+), Dy(3+), Ho(3+), Er(3+), and Tm(3+). Sm(3+), Eu(3+), and Gd(3+) samples were sensitive to humidity conditions because high- and low-hydration phases were interconvertible at a critical humidity of 10%, 20%, and 50%, respectively, as supported by both X-ray diffraction and gravimetry as a function of the relative humidity. In the phase conversion process, interlayer expansion or contraction of approximately 0.2 A also occurred as a possible consequence of absorption/desorption of H(2)O molecules. The hydration difference was also evidenced by refinement results. The number of coordinated water molecules per formula weight, n, changed from 6.6 for the high-hydration Gd sample to 6.0 for the low-hydration Gd sample. Also, the hydration number usually decreased with increasing atomic number; e.g., n = 7.4, 6.3, 7.2, and 6.6 for high-hydration Nd, Sm, Eu, and Gd, and n = 6.0, 5.8, 5.6, 5.4, and 4.9 for low-hydration Gd, Tb, Dy, Ho, and Er. The variation in the average Ln-O bond length with decreasing size of the lanthanide ions is also discussed. This family of layered lanthanide compounds highlights a novel chemistry of interplay between crystal structure stability and coordination geometry with water molecules.

General Synthesis and Structural Evolution of a Layered Family of Ln8(OH)20Cl4·nH2O (Ln = Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Y)

Preparation, phase equilibriums, crystal chemistry, and some properties of lanthanide hydroxide nitrates

Hydrothermal equilibriums and crystal growth of rare earth oxides, hydroxides, hydroxynitrates, and hydroxycarbonates

The plutonium-oxygen phase diagrams has been clarified by XPS and AES results which show that three oxygen-containing plutonium phases, PuO/sub 2/, ..cap alpha..-Pu/sub 2/O/sub 3/, and PuO/sub x/C/sub y/, are successively formed when oxide-coated plutonium metal is heated in vacuo to 500/sup 0/C. Formation of the oxide carbide is evidenced by the fact that a shift in the Pu(4f/sub 7/2/) binding energy is coincident with changes in the C(1s) photoelectron and C(KLL) Auger spectra, showing that unbound carbon is converted to carbide. The reaction conditions duplicate those at which plutonium monoxide reportedly forms and demonstrate that the NaCl-type surface phase previously identified as PuO is actually PuO/sub x/C/sub y/. The oxide carbide has a spectroscopically determined composition of PuO/sub 0.65+-0.15/C/sub 0.45+-0.15/ and reacts with CO, CO/sub 2/, and O/sub 2/ at low pressures to form PuO/sub 2/ and unbound carbon in a coherent product layer (approx. 20 nm thick) which retards further oxidation. Estimated thermodynamic data for PuO/sub x/C/sub y/ are consistent with the observed formation and oxidation reactions. The Pu(4f/sub 7/2/) binding energies for PuO/sub 2/, ..cap alpha..-Pu/sub 2/O/sub 3/, PuO/sub x/C/sub y/, and Pu are 426.1, 424.4, 423.6, and 422.2 eV, respectively.

John M. Haschke

Papers

Preparation, phase equilibriums, crystal chemistry, and some properties of lanthanide hydroxide nitrates

Hydrothermal equilibriums and crystal growth of rare earth oxides, hydroxides, hydroxynitrates, and hydroxycarbonates

XPS-AES characterization of plutonium oxides and oxide carbide. The existence of plutonium monoxide

The preparation and some properties of europium bromides and hydrated bromides.

Vaporization thermodynamics of europium monoxide