SOME NEW CRYSTALLINE APPROXIMANTS OF AL-PD-MN QUASI-CRYSTALS

In this letter we report new crystalline approximants found in Al-Pd-Mn alloys. In the Al70Pd20Mn10 alloy, two cubic approximants with a = 1.24 and 2.03 nm, corresponding to substituting the rational ratios 1/1 and 2/1, respectively, for the irrational tau = 1/2(1 + 5(1/2)) in the icosahedral quasicrystal, have been found. In an alloy with a somewhat lower Pd content, namely Al70Pd15Mn15, four orthorhombic approximants with a and c equal respectively to 1.26 and 1.48 nm (using 1/1 and 1/1 respectively to substitute for tau in two orthogonal non-equivalent twofold axes of the decagonal quasicrystal), 1.92 and 6.14 nm (2/1 and 5/3), 5.05 and 3.78 nm (5/3 and 3/2), and 8.4 and 6.2 nm (8/5 and 5/3) occurred. Their b parameter corresponding to the periodicity along the tenfold axis of the decagonal quasicrystal is 1.24nm.