Crystallographic evidence for the formation of a continuous series of mixed crystals between NiO and LiNiO2

The system NiO - Li1-xNi1+xO2, with 0 less than or equal to x less than or equal to 1 has to be considered as a continuous series of mixed crystals of one structure type (structure of alpha-NaFeO2). The substitution of one Ni2+ ion in NiO by a Li+ ion is accompanied by the oxidation of another Ni2+ ion to Ni3+. In the series NiO - Li1-xNi1+xO2 the Vegard rule holds true for both lattice constants a and c. The literature statements on the formation of different phases in the system NiO - Li1-xN1+xO2 are obviously misinterpretations of the X-ray data. A very simple low-temperature solution combustion technique was adopted in this study to prepare different samples of this mixed crystal series. The samples were characterized by inductively coupled plasma for elemental analysis and by X-ray powder diffraction and Rietveld refinement for structural analysis.