The monoclinic superstructure of the <i>M</i> ₂Pt₆Al₁₅ series (<i>M</i>=Ca, Sc, Y, La, Lu)

Abstract

Abstract The five ternary intermetallic compounds M 2 Pt 6 Al 15 ( M =Ca, Sc, Y, La, Lu) were prepared from the elements by arc-melting. The crystal structure was determined via single crystal X-ray diffraction. The title compounds crystallize in a superstructure of the RE 0.67 Pt 2 Al 5 type structure ( P 6 3 / mmc ) in the monoclinic crystal system with space group P 12 1 / m 1 (Sc 2 Pt 6 Al 15 : a =734.19(2), b =1628.96(10), c =734.19(2) pm, β =119.999(3)°; wR =0.0356, 3034 F 2 values, 68 variables). The superstructure can be derived by the superspace formalism using (3+2)D or (3+1)D interpretations of the diffraction data. The structural relation to the subcell structure is discussed on the basis of a group-subgroup scheme. In the crystal structure strongly bonded [Pt 2 Al 4 ] δ − slabs are alternatingly stacked with ordered layers containing M atoms and Al 3 triangles.