Study of an order-disorder phase transition on an atomic scale: the example of decagonal Al-Ni-Co quasicrystals

Structural reconfigurations of nanosheet arrays in layered minerals caused by wave irradiation: desorption mechanism of Cs from nanosheet edges

In layered minerals typically available in soil, there exists a high concentration of nanosheet edge sites formed by overlap among two-dimensional (2D) nanosheets, which act as heavily adhesive Cs chemisorption sites. Here, we propose the application of irradiation with ultrasonic waves in addition to microwaves employing ethylenediaminetetraacetic acid (EDTA) chelate to aid the decontamination of Cs from the nanosheet edges. The energy deposition by irradiation with both micro and ultrasonic waves is found to separate the overlap among the 2D nanosheets, succeeding in the desorption of Cs from the nanosheet edges. The decontamination of Cs became more prominent with ultrasonic irradiation owing to more efficient energy deposition than that with microwaves. The desorption mechanism is highlighted based on the results of systematic studies of the local structural reconfigurations of nanosheet arrays caused by wave irradiation. Surprisingly, not the aqueous solution nor interlayer water but constitution water triggers Cs desorption from the nanosheet edges, thus opening up a future decontamination strategy with a water saving system.

Element specificity of ortho-positronium annihilation for alkali-metal loaded SiO2 glasses

Momentum distributions associated with ortho-positronium (o-Ps) pick-off annihilation photon are often influenced by light elements, as, e.g., carbon, oxygen, and fluorine. This phenomenon, so-called element specificity of o-Ps pick-off annihilation, has been utilized for studying the elemental environment around the open spaces. To gain an insight into the element specificity of o-Ps pick-off annihilation, the chemical shift of oxygen 1s binding energy and the momentum distributions associated with o-Ps pick-off annihilation were systematically investigated for alkali-metal loaded SiO2 glasses by means of X-ray photoelectron spectroscopy and positron-age-momentum correlation spectroscopy, respectively. Alkali metals introduced into the open spaces surrounded by oxygen atoms cause charge transfer from alkali metals to oxygen atoms, leading to the lower chemical shift for the oxygen 1s binding energy. The momentum distribution of o-Ps localized into the open spaces is found to be closely correlated with the oxygen 1s chemical shift. This correlation with the deepest 1s energy level evidences that the element specificity of o-Ps originates from pick-off annihilation with orbital electrons, i.e., dominantly with oxygen 2p valence electrons and s electrons with lower probability.

Element-specific study of local segmental dynamics of polyethylene terephthalate upon physical aging

Time-dependent relaxation processes upon physical aging below the glass transition temperature have been studied in polyethylene terephthalate by high-precision dilatometry (DLT), differential scanning calorimetry (DSC), and element-specific positron and positronium (Ps) annihilation spectroscopy. The macroscopic volume change observed by DLT can be described by the Kohlrausch-Williams-Watts decay function, whereas changes in the relaxation enthalpies evaluated by DSC and free volumes probed by positron and Ps annihilation spectroscopy are reproduced by two superimposed exponentials. The multi-method approach reveals three kinds of relaxation processes with characteristic relaxation times: (a) fast Arrhenius-type β relaxation involving the instantaneous local segmental densification along with the exclusion of oxygen atoms from free volumes, (b) macroscopically observable non-Arrhenius-type α relaxation originated from a distribution of relaxation times due to the heterogeneous dynamics of solid-state- and liquid-state-like local segments, and (c) extremely slow Arrhenius-type α relaxation as the consequence of a uniform relaxation time solely due to the thermal dependence of nanometer-scale solid-state-like local segments.