5 research outputs found
Icosahedral quasicrystal and 1/1 cubic approximant in Au-Al-Yb alloys
A P-type icosahedral quasicrystal is formed in Au-Al-Yb alloy of which
6-dimensional lattice parameter a6D = 7.448 {\AA}. The composition of the
quasicrystal was analyzed to be Au51Al34Yb15. This quasicrystal is formed in
as-cast alloys, and is regarded as metastable because of decomposition into
other crystalline phases by annealing at 700 \degree C. Among Tsai-type
quasicrystals, this quasicrystal is situated just between Zn-Sc group with
smaller a6D and larger Cd-Yb group. Intermediate valence of Yb recently
observed in this quasicrystal may be due to this unique situation, namely
smaller major component Au-Al than in Cd-Yb.
The predominant phase in the annealed specimen is a 1/1 cubic approximant
with lattice parameter a = 14.500 {\AA} belonging to the space group Im-3 .
This phase is stable at the composition Au51Al35Yb14 at 700 \degree C. Rietveld
structural analysis indicated that the crystal structure is understood as
periodic arrangement of Tsai-type clusters each including four Au-Al atoms at
their centers. Chemical ordering of Au and Al is characteristics of this
approximant.Comment: 20 pages including 1 table and 7 figure
Neutron scattering study on spin correlations and fluctuations in the transition-metal-based magnetic quasicrystal Zn-Fe-Sc
Spin correlations and fluctuations in the 3d-transition-metal-based
icosahedral quasicrystal Zn-Fe-Sc have been investigated by neutron scattering
using polycrystalline samples. Magnetic diffuse scattering has been observed in
the elastic experiment at low temperatures, indicating development of static
short-range-spin correlations. In addition, the inelastic scattering experiment
detects a -independent quasielastic signal ascribed to single-site
relaxational spin fluctuations. Above the macroscopic freezing temperature
K, the spin relaxation rate shows Arrhenius-type behavior,
indicating thermally activated relaxation process. In contrast, the relaxation
rate remains finite even at the lowest temperature, suggesting a certain
quantum origin for the spin fluctuations below .Comment: To be published in Phys. Rev.
Icosahedral quasicrystals in Zn-T-Sc (T=Mn, Fe, Co, Ni) alloys
Starting from the Zn17Sc3 cubic approximant, new quasicrystal alloys were
searched by replacement of Zn with transition elements, T. In the cases of
T=Mn, Fe, Co and Ni, new icosahedral quasicrystals are formed in as-cast alloys
as major phases at the alloy compositions of Zn75T10Sc15. All these
quasicrystals belong to a primitive type, and have 6-dimensional lattice
parameters, a6D, ranging from 7.044 to 7.107 A. They have the valence electron
concentrations, e/a, ranging from 2.01 to 2.14, and almost the same ratios
between the edge-length of the Penrose tile, aR, and the averaged atomic
diameter d: aR/d~1.75. Moreover other Zn- and Cd-based quasicrystals including
the same type of atomic cluster, Tsai-type cluster, also have the same values
of e/a~2.1 and aR/d~1.75. The equality in e/a indicates that the Hume-Rothery
mechanism plays an important role for the formation of these quasicrystals.Comment: 9 pages, 2 tables, 3 figure