Structural and magnetic properties of Ni-Li oxides

Mixed Li-Ni oxides, Li_xNi_1-xO, are prepared by solid state reaction in the range 0.2≤x≤0.46 by annealing around 1000 K for various times. As reported in literature, above x=0.31 an ordered solid solution (OSS) is formed in which planes of pure Ni alternate with Li-Ni planes, whereas below x=0.2 only a fully disordered solid state solution (SSS) exists. We analyze the intermediate composition region 0.22≤x≤0.31 by fitting the X-ray patterns with a two-phases model using the Rietveld method: a SSS phase and an OSS phase where partial occupancy of the Ni-planes by lithium is allowed. The two phases coexist in the intermediate region, and no lithium is allowed in the Ni planes of the OSS phase; furthermore, the lithium contents of the OSS and SSS phases are approximately x ∼ 0.4 and x ∼ 0.2, respectively, and loss of lithium is associated with transformation of the OSS phase into SSS.⁷Li NMR data find evidence of a common magnetic behaviour of the samples containing the OSS phase which agrees with the X-ray findings. Paper presented at the 2nd Euroconference on Solid State Ionics, Funchal, Madeira, Portugal, Sept. 10–16, 1995