A NEW NICKEL(III) OXIDE FAMILY - MSR(3)NIO(6) (M=SC, IN, TM, YB AND LU)

The new phases M(III)Sr(3)Ni(III)O(6) have been prepared for M = Sc, I n, Tm, Yb and Lu. Thermogravimetric analysis indicates that these phas es are stoichiometric nickel(III) oxides. Rietveld refinement of their crystal structures from powder X-ray diffraction data confirms that t hey adopt the rhombohedral K4CdCl6- type structure (space group R (3) over bar c: a = 9.6595(2) and c = 10.8546(3) Angstrom for ScSr3NiO6). The M site is fully occupied for M = Sc and In, but a deficiency of sc attering for M = Tm, Yb and Lu is shown to be due to Ni substitution t hrough a simultaneous refinement of the YbSr3NiO6 structure using X-ra y and time-of-flight neutron diffraction data. The refined composition is (Yb0.83Ni0.17)Sr3NiO6. The magnetic susceptibilities of the M = Sc , In and Lu samples show Curie-Weiss behaviour down to 6 K; however, S cSr3NiO6 shows a broad transition between 250 and 290 K, with Curie-We iss behaviour above and below this anomaly. This transition is thought to be between the statically and dynamically Jahn-Teller distorted re gimes of octahedrally coordinated, low-spin Ni3+.