Dynamic response of physisorbed hydrogen molecules on lanthanide-modified zirconia nanoparticles

We investigated the microstructure and surface properties of ultrafine Ce- and Nd-modified zirconia powders by a joint adsorption-isotherm and neutron-scattering study. While the average pore size distribution and specific surface area can be determined by BET analysis of nitrogen adsorption, neutron inelastic scattering from surface adsorbed hydrogen provides additional information about the modulation of local potential energies over the substrate surfaces and distinguishes subtle differences in the microporous and mesoporous structure of the two samples

Synthesis and microstructure of powder and porous ZrO{sub 2} from hydrolysis process

Powder and porous ceramics of ZrO{sub 2} are useful as starting materials for composites, catalytic supports, and absorbates. ZrO{sub 2} is, in practice, used as promoter composition in automotive catalyst. Hydrolysis results in advantage on possible control of primary particle size and its dispersion/aggregate state. This study focuses on crystal structure, microstructure, and porous structure in powder and porous ceramics of ZrO{sub 2}. The agglomeration reaction was controlled by pH in a solution resulting from hydrolysis of aqueous ZrOCl{sub 2}. We used neutron diffraction, small angle neutron scattering, and BET adsorption. Results clarify some factors in the well-controlled processing using hydrolysis for porous ZrO{sub 2} ceramics

Phase diagram of the one-dimensional extended attractive Hubbard model for large nearest-neighbor repulsion

We consider the extended Hubbard model with attractive on-site interaction U and nearest-neighbor repulsions V. We construct an effective Hamiltonian H_{eff} for hopping t<<V and arbitrary U<0. Retaining the most important terms, H_{eff} can be mapped onto two XXZ models, solved by the Bethe ansatz. The quantum phase diagram shows two Luttinger liquid phases and a region of phase separation between them. For density n<0.422 and U<-4, singlet superconducting correlations dominate at large distances. For some parameters, the results are in qualitative agreement with experiments in BaKBiO.Comment: 6 pages, 3 figures, submitted to Phys. Rev.

The phonon densities of states of wurtzite AlN and ZrN

Phonons are thought to play a crucial role in the high thermal conductivity of wide-bandgap semiconductors AlN and ZrN. Using time-of-flight neutron spectroscopy, we have measured the phonon spectra of AIN and ZrN up to 300 MeV (2400 cm{sup {minus}1}). The one-phonon density of states (DOS) of AIN exhibits relatively sharp bands at about 033, 63, 83 and 91 MeV. In addition, distinct multiple-phonon excitations were observed at {approximately}173 and 255 MeV. The phonon DOS of ZrN displays similar features with the corresponding phonon energies shifted toward lower energies. The measured DOS of AlN is compared with results of molecular-dynamics simulations

Neutron scattering investigation of magnetic excitations at high energy transfers

With the advance of pulsed spallation neutron sources, neutron scattering investigation of elementary excitations in magnetic materials can now be extended to energies up to several hundreds of MeV. We have measured, using chopper spectrometers and time-of-flight techniques, the magnetic response functions of a series of d and f transition metals and compounds over a wide range of energy and momentum transfer. In PrO/sub 2/, UO/sub 2/, BaPrO/sub 3/ and CeB/sub 6/ we observed crystal-field transitions between the magnetic ground state and the excited levels in the energy range from 40 to 260 MeV. In materials exhibiting spin-fluctuation or mixed-valent character such as Ce /sub 74/Th /sub 26/, on the other hand, no sharp crystal-field lines but a broadened quasielastic magnetic peak was observed. The line width of the quasielastic component is thought to be connected to the spin-fluctuation energy of the 4f electrons. The significance of the neutron scattering results in relation to the ground state level structure of the magnetic ions and the spin-dynamics of the f electrons is discussed. Recently, in a study of the spin-wave excitations in itinerant magnetic systems, we have extended the spin-wave measurements in ferromagnetic iron up to about 160 MeV. Neutron scattering data at high energy transfers are of particular interest because they provide direct comparison with recent theories of itinerant magnetism. 26 references, 7 figures

Neutron-scattering studies of nitride, oxide, and phosphate ceramics and their relationship with molecular-dynamics simulations of high-temperature properties

Currently, the strength and reliability of nitride and carbide ceramics are not sufficient to meet the demands of high-tech applications such as heat engines. A large R and D effort is needed to advance the field of ceramic science and engineering. The strength of ceramics depends on both the nature of atomic bonding such as covalency versus ionicity and the microstructure such as flaws and stress within the materials. The length scale of these influential factors ranges from 0.1 to 5,000 nm, thus presenting a challenge to experimentalists for a complete, quantitative characterization. The method of neutron scattering provides distinct advantages. In this paper, the authors present the neutron-scattering results of several important nitride oxide, and phosphate ceramics and point out the connections between the neutron data and computer simulations towards the goal of designing high-temperature materials

Preparation and characterization of nanofibrous filtering media

10.1016/j.memsci.2006.06.030Journal of Membrane Science2831-2209-218JMES

Intermultiplet transitions in rare-earth metals

We report here on direct observations of intermultiplet (IM) transitions in the rare-earth metals, Pr, Nd and Tb, made using the chopper spectrometers at the Intense Pulsed Neutron Source of Argonne National Laboratory. Despite hydrogen contamination of the polycrystalline samples, we have observed inelastic peaks at small Q arising from IM transitions in Pr (approx.260 MeV), Nd (approx.242 MeV) and Tb (approx.256 MeV) although the latter has not yet been observed unambiguously. Future work will investigate the energy level structure and dynamical properties of rare-earth ions in stoichiometric metallic systems. 5 refs., 3 figs

The diffusion of H{sub 2} in hexagonal ice at low temperature

We have studied the diffusive motion of hydrogen in D{sub 2}O ice by measuring the quasielastic scattering and estimating the single particle diffusion coefficient of hydrogen

The diffusion of H{sub 2} in hexagonal ice at low temperature

We have studied the diffusive motion of hydrogen in D{sub 2}O ice by measuring the quasielastic scattering and estimating the single particle diffusion coefficient of hydrogen