Magnetic and electrochemical studies on Ni2+-substituted Li-Mn spinel oxides -: art. no. 093905

LiMn2-xNixO4 (x < 0.5) cubic spinel oxide was synthesized by the sol-gel technique using Li-nitrate, Mn-acetate, and Ni-acetate salts. The gel precursors were decomposed at 300 degrees C in air and then annealed at temperatures ranging from 500 to 850 degrees C in an oxygen flow. For a fixed annealing temperature of 700 degrees C, the lattice constant linearly decreased with an increase in the substitution degree x. As x increased, the low-temperature magnetization increased and the asymptotic Curie temperature moved in the positive direction and changed its sign from negative to positive around x=0.2. Additionally, the redox capacity of 4.7 V plateau was increased at the expense of the capacity around 4.0 V. When the x value was fixed at 0.5, all the specimens showed ferromagnetic magnetization. The minimum lattice parameter, the maximum Curie temperature, and the maximum magnetization were attained simultaneously for the specimen annealed at 700 degrees C, which exhibited only a plateau around 4.7 V. It was possible to explain these variations by considering the magnetic interactions between transition-metal ions.