Japan Atomic Energy Research Institute

About: Japan Atomic Energy Research Institute is a based out in . It is known for research contribution in the topics: Neutron & Irradiation. The organization has 7707 authors who have published 14471 publications receiving 207688 citations.

Electronic structure and spectroscopy of the quaternary Heusler alloy Co2Cr1−xFexAl

Abstract: Quaternary Heusler alloys Co2Cr1 xFexAl with varying Cr to Fe ratio x were investigated experimentally and theoretically. The electronic structure and spectroscopic properties were calculated using the full relativistic Korringa-Kohn-Rostocker method with coherent potential approximation to account for the random distribution of Cr and Fe atoms as well as random disorder. Magnetic effects are included by the use of spin dependent potentials in the local spin density approximation. Magnetic circular dichroism in X-ray absorption was measured at the L2,3 edges of Co, Fe, and Cr of the pure compounds and the x = 0.4 alloy in order to determine element specific magnetic moments. Calculations and measurements show an increase of the magnetic moments with increasing iron content. Resonant (560eV - 800eV) soft X-ray as well as high resolution - high energy (� 3.5keV) hard X-ray photo emission was used to probe the density of the occupied states in Co2Cr0.6Fe0.4Al.

Positron annihilation study of vacancy-solute complex evolution in Fe-based alloys

Abstract: Irradiation-induced vacancy-type defects in Fe-based dilute binary alloys (Fe-C, Fe-Si, Fe-P, Fe-Mn, Fe-Ni, and Fe-Cu), model alloys of nuclear reactor pressure vessel steels, are studied by positron annihilation methods, positron lifetime, and coincidence Doppler broadening (CDB) of positron annihilation radiation. The vacancy-type defects were induced by 3 MeV electron irradiation at room temperature. The defect concentrations are much higher than that in pure Fe irradiated in the same condition, indicating strong interactions between the vacancies and the solute atoms and the formation of vacancy-solute complexes. The vacancy-solute complexes in the Fe-Cu, Fe-Ni, and Fe-C alloys are definitely identified by the CDB technique. In particular, the single vacancies in Fe-Cu are surrounded by Cu atoms, resulting in vacancy--multi-Cu-atom complexes of $V\ensuremath{-}{\mathrm{Cu}}_{n}$ $(ng~6).$ The vacancy clusters are formed in Fe-Ni and Fe-P, while they are not observed in the other alloys. The isochronal annealing behavior is also studied. The ultrafine Cu precipitates coherent with the Fe matrix are formed in Fe-Cu after annealing at 350 \ifmmode^\circ\else\textdegree\fi{}C, while the other alloys show complete recovery without forming any precipitate that traps the positrons.

Phase-Change Materials: Vibrational Softening upon Crystallization and Its Impact on Thermal Properties

Abstract: Crystallization of an amorphous solid is usually accompanied by a signifi cant change of transport properties, such as an increase in thermal and electrical conductivity. This fact underlines the importance of crystalline order for the transport of charge and heat. Phase-change materials, however, reveal a remarkably low thermal conductivity in the crystalline state. The small change in this conductivity upon crystallization points to unique lattice properties. The present investigation reveals that the thermal properties of the amorphous and crystalline state of phase-change materials show remarkable differences such as higher thermal displacements and a more pronounced anharmonic behavior in the crystalline phase. These fi ndings are related to the change of bonding upon crystallization, which leads to an increase of the sound velocity and a softening of the optical phonon modes at the same time.