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The dependence of chemical composition on the average sizes of subnanometer-scale intrinsic structural open spaces surrounded by glass random networks in two-component silica-based glasses was investigated systematically using positronium (Ps) confined in the open spaces. The average sizes of the open spaces for SiO2-B2O3 and SiO2-GeO2 glasses are only slightly dependent on the chemical compositions because the B2O3 and GeO2 are glass network formers that are incorporated into the glass network of the base SiO2. However, the open space sizes for all SiO2-R2O (R=Li, Na, K) glasses, where R2O is a glass network modifier that occupies the open spaces, decrease rapidly with an increase in the R2O concentration. Despite the large difference in the ionic radii of the alkali metal (R) atoms, the open space sizes decrease similarly for all the alkali metal atoms studied. This dependence of the chemical composition on the open space sizes in SiO2-R2O observed by Ps shows that the alkali metal atoms do not randomly occupy the structural open spaces, but filling of the open spaces by R2O proceeds selectively from the larger to the smaller open spaces as the R2O concentrations are increased. [ABSTRACT FROM AUTHOR]

Jahn–Teller (JT) distortion of the diamagnetic neutral divacancy (V20) in Si is studied by positron annihilation spectroscopy. Based on the anisotropy of electron momentum distribution around the divacancies obtained by two-dimensional angular correlation of positron annihilation radiation (2D-ACAR) technique, the preferred alignment of the divacancy in a specimen by compressing uniaxial stress along the [0 1 1] axis is detected. The direction of the alignment evidences the pairing JT distortion rather than the resonant bonding distortion, which is similar to the distortion in the singly negative divacancy (V2−). [Copyright &y& Elsevier]

Abstract: We present a microstructural study of a surveillance test specimen from a reactor pressure vessel steel of a Russian-type nuclear reactor after neutron irradiation, post-irradiation annealing and re-irradiation, using atom probe tomography (APT) and positron annihilation spectroscopy (PAS). The APT results showed the formation of Cu-rich solute nano-clusters (CRCs) during the initial irradiation and their subsequent coarsening during annealing. After re-irradiation, new CRCs have been observed. The irradiation-hardening almost recovered during annealing. However, by re-irradiation, hardening comparable to that by the initial irradiation was observed. The hardening due to the CRCs formed during the initial irradiation, estimated using the Russell–Brown model, was almost the same as that observed. However, the estimated hardening after the re-irradiation was about half of the measured one. The other hardening is attributed to the newly formed MDs by the re-irradiation, which was evidenced by PAS. [Copyright &y& Elsevier]