Disordered microtwinned (Sc1-x)Sc4Co6Sn18 (x=0.14)

The crystal structure and composition of (Sc1-x)Sc4Co6Sn18 (x = 0.14) were refined from single crystal X-ray diffraction data. The structure is disord ered microtwinned tetragonal, I4(1)/acd, a = 13.341(8), c = 26.69(2) Angstr om, V = 4749.8 Angstrom(3), Z = 8, D-x = 7.58 g cm(-3), M-r = 2708.5, mu = 23.85 mm(-1), 73 refined parameters, R = 0.0638 for 1639 observed unique re flections with F-0 > 4 sigma(F-0). The title compound belongs to a large se ries of stannides with formula (M1-xSnx)M4M'Sn-6(18) (M = rare earth, M' = Co, Ru, Rh, Ir, Os) and two related structures (tetragonal phase II with ce ll parameters a approximate to 13.7, c approximate to 27.4 Angstrom and pse udo-cubic phase II' (earlier sometimes called phase III) with a approximate to 13.7 Angstrom, which was explained as microtwinned phase II). The cryst al was microtwinned. The refined volume fractions of three twin domains wer e 0.381(7), 0.287(7) and 0.332(7), respectively. A microtwinning of phase I I seems to be an intrinsic feature of its structure thus reducing the proba bility of the formation of the ideal cubic structure II' during the crystal growth.