New barium rare-earth nickel oxides: Synthesis, crystal structure, and magnetic order

Crystals of isostructural R8Ba5Ni4O21 (R = Y, Er, Tm, Yb, and Lu) have been obtained. Conditions for synthesis and stability are reported. The crystal structures of these materials have been established by single-crystal X-ray diffraction: space group I4/m with cell-parameters a =13.713(1) and 13.666(3) Angstrom, c = 5.692(1) and 5.673(2) Angstrom for R = Y and Er, respectively. The compounds contain square NiO5 pyramids, trigonal RO7 prisms capped on one rectangular face, tetragonal bicapped Ba(1)O-10 prisms, and irregular Ba(2)O-10 polyhedra. A comparison is made between this structure type and those of R2BaNiO5 and R2BaCuO5. Their structure and properties show close relations. The temperature dependence of the magnetic susceptibility from 350 to 1.8 K, measured for R = Y, Yb, and Er, shows the presence of antiferromagnetic ordering for the Yb and Er compounds.