(3+1)D superspace structural determination of two new modulated composite phases: Sr 1+ x(Cu xMn 1− x)O 3; x=3/11 and x=0.3244

Abstract

We report the structure determination of two new phases belonging to the A 1+ x (A′ x B 1− x )O 3 family of oxides with A=Sr, A′=Cu, and B=Mn, where x=3/11 and x=0.3244, corresponding to a commensurate and incommensurate composite structure, respectively. These two compounds are the first examples of oxides belonging to the Sr 1+ x (Cu x Mn 1− x )O 3 family. Their structures were solved in the (3+1) dimensional superspace formalism as modulated composite structures with two subsystems [(Cu,Mn)O 3] and [Sr]. The superspace group used to solve the structures is R 3 ̄ m(00γ)0s . The first phase ( x=3/11), corresponding to the chemical formula Sr 14Cu 3Mn 8O 33, was obtained as a single crystal with unit cell parameters of a=9.6025(3) Å and c 1=2.5660(8) Å ( q =7/11 c 1 ∗ , Z=3), where c 1 is the lattice parameter corresponding to the c-axis of the trigonal subsystem [(Cu,Mn)O 3]. The second phase ( x=0.3244(1)), is a polycrystalline sample with unit cell parameters of a=9.5933(7) and c 1=2.5933(3) ( q =0.6622 c 1 ∗ , Z=3). In both structures, one dimensional chains run along the c-axis which contain octahedra and trigonal prisms occupied by manganese and copper atoms, respectively. The refinement results show that in both cases copper occupies the rectangular faces of the trigonal prism while manganese occupies the octahedral sites. The magnetic measurements of the polycrystalline phase (Sr 1+ x (Cu x Mn 1− x )O 3, x=0.3244(2)) and the Curie constant obtained from the high temperature susceptibility are in agreement with a spin state configuration of S=3/2 for Mn 4+ and S=1/2 for Cu 2+.