Pair distribution function and structure factor of spherical particles

The availability of neutron spallation-source instruments that provide total scattering powder diffraction has led to an increased application of real-space structure analysis using the pair distribution function. Currently, the analytical treatment of finite size effects within pair distribution refinement procedures is limited. To that end, an envelope function is derived which transforms the pair distribution function of an infinite solid into that of a spherical particle with the same crystal structure. Distributions of particle sizes are then considered, and the associated envelope function is used to predict the particle size distribution of an experimental sample of gold nanoparticles from its pair distribution function alone. Finally, complementing the wealth of existing diffraction analysis, the peak broadening for the structure factor of spherical particles, expressed as a convolution derived from the envelope functions, is calculated exactly for all particle size distributions considered, and peak maxima, offsets, and asymmetries are discussed.Comment: 7 pages, 6 figure

Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics

Uranium and plutonium's 5f electrons are tenuously poised between strongly bonding with ligand spd-states and residing close to the nucleus. The unusual properties of these elements and their compounds (eg. the six different allotropes of elemental plutonium) are widely believed to depend on the related attributes of f-orbital occupancy and delocalization, for which a quantitative measure is lacking. By employing resonant x-ray emission spectroscopy (RXES) and x-ray absorption near-edge structure (XANES) spectroscopy and making comparisons to specific heat measurements, we demonstrate the presence of multiconfigurational f-orbital states in the actinide elements U and Pu, and in a wide range of uranium and plutonium intermetallic compounds. These results provide a robust experimental basis for a new framework for understanding the strongly-correlated behavior of actinide materials.Comment: 30 pages, concatenated article and supporting information, 10 figure

Interrelation between the pseudogap and the incoherent quasi-particle features of high-Tc superconductors

Using a scenario of a hybridized mixture of localized bipolarons and conduction electrons, we demonstrate for the latter the simultaneous appearance of a pseudogap and of strong incoherent contributions to their quasi-particle spectrum which arise from phonon shake-off effects. This can be traced back to temporarily fluctuating local lattice deformations, giving rise to a double-peak structure in the pair distribution function, which should be a key feature in testing the origin of these incoherent contributions, recently seen in angle-resolved photoemission spectroscopy (ARPES).Comment: 4 pages, 3 figures, to be published in Phys. Rev. Let

Quantum and Thermal Phase Transitions of Halogen-Bridged Binuclear Transition-Metal Complexes

Aiming to settle the controversial observations for halogen-bridged binuclear transition-metal (MMX) complexes, finite-temperature Hartree-Fock calculations are performed for a relevant two-band Peierls-Hubbard model. Thermal, as well as quantum, phase transitions are investigated with particular emphasis on the competition between electron itinerancy, electron-phonon interaction and electron-electron correlation. Recently observed distinct thermal behaviors of two typical MMX compounds Pt_2(CH_3CS_2)_4I and (NH_4)_4[Pt_2(P_2O_5H_2)_4I]2H_2O are supported and further tuning of their electronic states is predicted.Comment: 5 pages, 3 figures embedded, to be published in J. Phys. Soc. Jpn. Vol.70, No.5 (2001

Competing Ground States of the New Class of Halogen-Bridged Metal Complexes

Based on a symmetry argument, we study the ground-state properties of halogen-bridged binuclear metal chain complexes. We systematically derive commensurate density-wave solutions from a relevant two-band Peierls-Hubbard model and numerically draw the the ground-state phase diagram as a function of electron-electron correlations, electron-phonon interactions, and doping concentration within the Hartree-Fock approximation. The competition between two types of charge-density-wave states, which has recently been reported experimentally, is indeed demonstrated.Comment: 4 pages, 5 figures embedded, to appear in J. Phys. Soc. Jp

Blue space as caring space – water and the cultivation of care in social and environmental practice

This paper studies three sites or ‘landscapes of care’ in Leeds, Bristol and London where water and associated built and natural environments are used to co-construct and facilitate forms of social and environmental care. Our research narrates the ways in which blue spaces are cultivated for the production of particular forms of caring bodies and sensibilities. Interpreting care as both a doing (caring for) and emotion (caring about), we draw attention to the diverse practices and distributed nature of care in these environments. Our paper has three main insights. First, we draw attention to the role of water as both a material and site of care. Second, we identify a range of more-than-human benefits associated with blue spaces and how these emerge via collaborative, non-linear and reciprocal forms of care. Third, we argue that by understanding how care works in everyday social practice, new forms of ecological care and pro-environmental ways of living with the world can emerge

Studies of Vibrational Properties in Ga Stabilized d-Pu by Extended X-ray Absorption Fine Structure

Temperature dependent extended x-ray absorption fine structure (EXAFS) spectra were measured for a 3.3 at% Ga stabilized Pu alloy over the range T= 20 - 300 K at both the Ga K-edge and the Pu L_III-edge. The temperature dependence of the pair-distance distribution widths, \sigma(T) was accurately modeled using a correlated-Debye model for the lattice vibrational properties, suggesting Debye-like behavior in this material. We obtain pair- specific correlated-Debye temperatures, \Theta_cD, of 110.7 +/- 1.7 K and 202.6 +/- 3.7 K, for the Pu-Pu and Ga-Pu pairs, respectively. These results represent the first unambiguous determination of Ga-specific vibrational properties in PuGa alloys, and indicate the Ga-Pu bonds are significantly stronger than the Pu-Pu bonds. This effect has important implications for lattice stabilization mechanisms in these alloys.Comment: 7 pages, 4 figures, Phys. Rev. B in pres