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Tsai-Type Quasicrystal and Its Approximant in Au-Al-Tm Alloys

100%

Tanaka K., Tanaka Y., Ishimasa T., Nakayama M., Matsukawa S., Deguchi K., Sato N.

vol. 126

issue 2

603-607

A P-type icosahedral quasicrystal with a six-dimensional lattice parameter a_{6D} = 7.411 Å is formed as an equilibrium phase in Au-Al-Tm alloy, of which composition was analyzed to be Au_{46}Al_{38}Tm_{16} by electron probe microanalysis. This quasicrystal is observed as a predominant phase in both as-cast and Au_{49}Al_{34}Tm_{17} alloys annealed at 910°C, and as one of main phases in the alloy slowly cooled from 1020°C. A 1/1 approximant, Au_{48}Al_{38}Tm_{14}, is also formed near the composition of the quasicrystal. This is a body-centered cubic structure (space group: Im3̅) with a lattice parameter a = 14.458 Å that is an isostructure to the recently reported 1/1 Tsai-type approximant in Au-Al-Yb. This approximant is characterized by disorderly arranged four Au-Al atoms centered at the Tsai-type cluster, presence of atoms at 8c site, and chemical ordering of Au and Al at sites forming a partial triacontahedron.

Transport Properties of the Au-Al-Yb Quasicrystal and Approximant under Hydrostatic Pressure

84%

Matsukawa S., Tanaka K., Nakayama M., Kunikata S., Deguchi K., Imura K., Ishimasa T., Sato N.

vol. 126

issue 2

527-530

The mixed-valence Au-Al-Yb quasicrystal exhibits unusual quantum criticality. Its crystalline approximant behaves like a conventional heavy fermion metal. Due to these novel features, they have attracted much attention recently. To examine the sample dependence of this new type of materials, we have prepared several samples and measured the electrical resistivity both at ambient and high pressures as well as the magnetic susceptibility at ambient pressure. The residual resistivity ratio of the quasicrystals is almost sample independent while the power law exponent n of the electrical resistivity varies from sample to sample. The effective magnetic moment p_{eff} of the quasicrystals is also sample dependent, ranging from about 3.4 to 3.9 μ_{B}/Yb, and these values are all smaller than the free Yb^{3+} ion value, confirming the mixed-valence nature. Although the magnitude of n and p_{eff} is sample-dependent, the principal feature of the mixed-valence is confirmed in all the samples studied thus far. A combination of these results indicates correlation between n and p_{eff}, suggesting that the 4f electrons may contribute to a scattering mechanism of the conduction electrons. External pressure increases the magnitude of the electrical resistivity and decreases the index n of both the quasicrystal and the approximant. Up to the highest pressure measured in the present study no experimental evidence for a phase transition was found.

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2 Acta Physica Polonica A

2 2014

2 Deguchi K.

2 Ishimasa T.

2 Matsukawa S.

2 Nakayama M.

2 Sato N.

2 Tanaka K.

1 Imura K.

1 Kunikata S.

1 Tanaka Y.

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Tsai-Type Quasicrystal and Its Approximant in Au-Al-Tm Alloys

Transport Properties of the Au-Al-Yb Quasicrystal and Approximant under Hydrostatic Pressure