Solid-state reaction study on the system Ni-Li 2CO 3

Abstract

Thermogravimetry, differential scanning calorimetry, X-ray diffractometry and scanning electron microscopy have been used to investigate the formation reaction of the solid solution Li x Ni 1− x O in the solid-state system Ni-Li 2CO 3. Thermogra vimetric results show that carbonate decomposition takes place well below its usual temperature when nickel is being oxidized and that as a consequence of the simultaneous oxidation and decomposition processes, a solid solution forms in a temperature range where no appreciable volume diffusion can occur. X-ray diffraction measurements confirm this conclusion showing that lattice constant values of thermogravimetric samples linearly decrease with increasing mixture lithium content. Notwithstanding all experimental evidences agree in indicating that all lithium oxide participates to solid solution formation, sensible departures from the linear relationship arise for mixtures of high lithium content (X Li>0.2010). It is shown that cation vacancies are responsible of such a behaviour and that their concentration increases with increasing the relative amount of lithium oxide produced by spontaneous carbonate decomposition that enters solid solution.