Structures and properties of Ni$^{1+/2+}$ nickelates with infinite NiO$_{2}$ layers

Layered mixed valence Ni$^{1+/2+}$ nickelates possess similar crystal and electronic structures to Cu$^{2+/3+}$ high temperature superconducting cuprates. Only a few Ni$^{1+/2+}$ nickelates have been identified and they properties have not been reported so far. We present a first systematic study of Ln$_{n+1}$Ni$_{n}$O$_{2n+2}$, Ln = La or Nd, which structures could be described as an intergrowth of {\{}LnO$_{2}${\}} fluorite and infinite layer {\{}LaNiO$_{2}${\}}$_{n}$ blocks. The crystal structures of the new Ln$_{3}$Ni$_{2}$O$_{6,}$ Ln$_{4}$Ni$_{3}$O$_{8,}$ Ln$_{5}$Ni$_{4}$O$_{10}$ phases have been confirmed by X-ray and neutron powder diffraction. X-ray absorption spectroscopy data proves the 1+/2+ oxidation state and planar coordination of Ni atoms. Magnetic susceptibility data of Ln$_{n+1}$Ni$_{n}$O$_{2n+2}$ will be discussed.