Crystal structure of a cubic Al₆₇Pd₁₁Mn₁₄Si₇; a new 1/1 rational approximant for the Al-Pd-Mn icosahedral phase

The structure of a cubic Al_67.4Pd_11.4Mn_14.4Si_6.8 phase, which is referred as an 1/1 rational approximant of an icosahedral phase, was determined by means of single crystal X-ray structural analysis: space group Pm3 (No. 200), a = 12.281(1) Ä, V = 1852.0(3) ij MoK_a (? = 0.71069 Ä); refined as Al_66.3Pd_12.0Mn_14.7Si_7.0, atom/ cell = 122.72, F(000) = 2305, µ - 7.54 mm^-1, D_calc = 4.47 Mgm^-3, R = 0.0319 for the observed 703 reflections with I > 2.0s(I). An atom cluster with about 13 Ä in diameter is found at the origin of a unit cell and the cubic arrangement of these clusters through the shared edges can reproduce the present 1/1 approximant structure. This atom cluster is ranked into five atomic shells, where the atomic arrangement analogous to the Bergman cluster is clearly identified. The clusters of Bergman’s derivation are suggested to be one of the most essential cluster units for the face-centered icosahedral quasicrystals.