THE STRUCTURE AND PROPERTIES OF AN UNUSUAL NEW NICKEL(III) OXIDE - YSR5NI3O11

An investigation of the system Y2-xSrxNiO4-δ has shown that a stable phase exists only at x = 1.67 between 1100 and 1150°C. Thermogravimetric analysis gives the oxygen deficiency as δ = 0.33(1), showing that the phase is a stoichiometric nickel(III) oxide, YSr5Ni3O11 (Y0.33Sr1.67NiO3.67). Rietveld refinement using powder X-ray diffraction data confirms that YSr5Ni3O11 adopts the tetragonal K2NiF4 (T-type) structure (I4/mmm, Z = 2 3, a = 3.7762(1), c = 12.3011(4) Å, Rwp = 3.9%). Independent refinement of the oxygen site occupancies reveals that the oxygen vacancies are present in the nickel oxide planes. Magnetic susceptibility data for YSr5Ni3O11 at 5-350 K show Curie-Weiss behavior characteristic of low spin Ni3+ with μeff = 1.76 and Θ = - 10.8 K. Four-probe dc electronic conductivity measurements show that the material is a semiconductor between 7 and 300 K. These data are well fitted by a two-dimensional variable range hopping model. © 1993 Academic Press, Inc.