The structure, characterization, and magnetic properties of Ca4-xNixIrO6 (x = 0.25, 0.5)

Ca4-xNixIrO6 (x=0.25, 0.5) crystallizes with trigonal (rhombohedral) symmet ry in the space group R(3) over bar c, Z = 6, for Ca3.75Ni0.25IrO6 a = 9.30 13(1) Angstrom, c = 11.1554(1) Angstrom; for Ca3.5Ni0.5IrO6 a = 9.2723(1) A ngstrom, c = 11.0825(1) Angstrom. Ca3.75Ni0.25IrO6 and Ca3.5Ni0.5IrO6 are i sotypic to compounds of the Sr4PtO6 structure type. The structure of Ca3.75 Ni0.25IrO6 has been solved by means of single crystal X-ray diffraction dat a analysis with the reliability factors of R = 0.019 and R-w = 0.022. Also, both structures have been determined by Rietveld refinement of powder X-ra y diffraction data. The structure consists of chains of alternating face-sh aring IrO6 octahedra and (Ca/Ni)O-6 trigonal prisms. The chains are separat ed by the calcium cations which are in a distorted square antiprismatic coo rdination. Magnetic measurements revealed that both Ca3.75Ni0.25IrO6 and Ca 3.5Ni0.5IrO6 follow Curie-Weiss behavior at high temperatures. Ca3.75Ni0.25 IrO6 undergoes a single antiferromagnetic transition at T-N = 5 K whereas C a3.5Ni0.5IrO6 undergoes two antiferromagnetic transitions at T-N1 = 13 K an d T-N2 = 4 K.