Structure of the incommensurate composite crystal [Sr₂Cu₂O₃][CuO₂] _x (x = 1.436)

Abstract

[Sr 2 Cu 2 O 3 ][CuO 2 ] x (x=1.436), M r =487.5, orthorhombic, M A21 1 m s a 1 .M A21 1 m s a 1 , a=11.457 (5), b=13.409(9), c 1 =3.395 (3), c 2 =2.740 (2) A, k 1 =b * + 1.436 (2)c 1 * , k 2 =b * +0.696 (1)c 2 * , V 1 =604.5, V 2 = 420.9 A 3 , Z=4, D x =5.36 Mg m -3 , Mo Kα, λ= 0.71073 A, μ=28.5 mm -1 , F(000)=890.5, room temperature, final R=0.057 for 314 unique reflections. The first subsystem [Sr 2 Cu 2 O 3 ] is composed of (Cu 2 O 3 )∞ shetts perpendicular to the b axis and Sr ions coordinated to the sheet. The second subsystem is (CuO 2 )∞ infinite chains parallel to the c axis, which are located among the Sr ions of the first subsystem. The atomic positions are modulated along the c axis by the interactions between the two subsystems