Al Rh Research Articles

Structure of the AlRhCu decagonal quasicrystal: II. A higher-dimensional description

A higher-dimensional description has been applied to the structural model of the AlRhCu decagonal quasicrystal described in a unit-cell approach in the previous paper (Part I), which was proposed on the basis of a high-resolution electron microscopic study. The structure of the AlRhCu decagonal quasicrystal consists of two layers in a period, which are related by 10 5 screw axis. The independent layer is described by two hyper-atoms in the five-dimensional structure. Hyper-atoms of the AlRhCu DQC are at special positions with the site symmetry 5 m, the acceptance domain of the AlRhCu decagonal quasicrystal in the internal (perpendicular) space can be viewed as the extensions of those for the Penrose tiling. The geometric and chemical structures of these hyper-atoms are described in detail. A projection of the five-dimensional structure into the external (physical) space generates the ideal quasiperiodic structure of the AlRhCu decagonal quasicrystal mentioned in the previous paper (Part I).

Positron annihilation study in binary molecular solid solutions of metal acetylacetonate complexes using positron annihilation lifetime (PAL) and Doppler broadening (DBS) spectroscopies

PAL and DBS techniques have been used to study inhibition of positronium (Ps) formation in binary molecular solid solutions of Al(III) (tris)-acetylacetonate (acac), as matrix, and Co(III), Fe(III), Ru(III), Rh(III), and Ir(III) (tris)-acetylacetonates, as guest molecules. For all the studied systems, no Ps quenching reactions have been observed. For Al (1− x) Co ( x) (acac) 3, Al (1− x) Fe ( x) (acac) 3, and Al (1− x) Ru ( x) (acac) 3 systems, a strong inhibition of Ps formation was observed with increasing of guest molecule concentration. The obtained Ps yields measured by PAL were fitted by the Stern-Volmer equation. The DBS results confirm the inhibition constants ( k) previously determined by PAL technique, except for the Al (1− x) Ru ( x) (acac) 3 system, where the experimental and calculated Doppler broadening curves are quite different. Only in Al (1− x) Ir ( x) (acac) 3 system, the inhiition effect was not detected. The highest total inhibition constants belong to Al (1− x) Co ( x) (acac) 3 and Al (1− x) Ru ( x) (acac) 3 systems and the smallest one to Al (1− x) Rh ( x) (acac) 3 system. The magnitude of the obtained k values was associated with the ability of the guest complexes to scavenge electrons and are closely related to the redox properties of the complexes. X-ray diffraction measurements were made to confirm the hypothesis that all studied samples are single phase systems and that the introduction of the guest molecules in the matrix lattice does not result in significant crystalline changes. These results are well explained in the framework of the spur model and show that the chemical properties determine the Ps yields in molecular solids, regardless of their free volume characteristics.

Lattice site occupation and precipitate dissolution of implanted and irradiated Al(Rh) and Al(Ir)

Abstract The apparent substitutional fraction, fs , of Rh and Ir implanted into Al single crystals at 293 K with peak concentrations of 0.17±0.01 at.% is 0.57 ± 0.02 and 0.47±0.02, respectively. Upon annealing to 593 K fs decreases and the critical angles of the impurities narrow due to partially coherent precipitate formation. Irradiation with 300 keV Ar ions at 77 K with deposited energy densities up to 20 dpa leads to precipitate dissolution accompanied by an increase of fs up to 0.70±0.02 for Al(Rh) and 0.82±0.02 for Al(Ir). The relatively high fs values do not decrease during annealing from 77 K to 293 K, indicating that vacancy trapping is not a dominant process. Precipitate formation seems therefore to limit the maximum obtainable fs values during implantation at 293 K for these systems.

Quasicrystals in rapidly solidified alloys of AlPt group metals-III. Quasicrystals in rapidly solidified AlRh and AlIr alloys

Decagonal quasicrystals were found in both rapidly solidified Al 5Rh and Al 5Ir alloys with a periodicity of about 1.6 nm along the tenfold axis. Apart from the already known intermetallic phases Al 9Rh 2 and Al 9Ir 2, two new hexagonal AlIr phases have been found. One is metastable and isostructural with the hexagonal α-AlFeSi, consisting of many icosahedral subunits in its structure and the other has lattice parameters a ≈ 0.31 nm and c ≈ 0.52 nm.