Effect of Li 2O-doping on the thermal stability of cobaltic oxide

Abstract

The influence of lithium oxide-doping on the thermal stability of Co 3O 4 was studied using DTA, TG, DTG and X-ray diffraction techniques. Pure and doped cobaltic oxide specimens were prepared by thermal decomposition of pure basic cobalt carbonate and the basic carbonate mixed with different proportions of LiOH, in air, at different temperatures between 500 and 1100°C. Pure Co 3O 4 was found to start partial decomposition when heated in air at 830°C yielding the CoO phase. The complete decomposition was effected by heating at 1000°C. Doping of Co 3O 4 with different proportions of Li 2O was found to much increase its thermal stability. The temperatures at which the doped oxide samples started to undergo decomposition were increased to 865, 910 and 1050°C for 0.375, 0.75 and 3% Li 2O-doped solids, respectively. The DTA revealed that the 1.5% Li 2O-doped cobaltic oxide did not undergo any thermal decomposition till 1080°C. The X-ray investigation showed that the prolonged heating of 1.5 and 3% Li 2O-doped solids at 1100°C for 36 h effected only a partial decomposition of Co 3O 4 into CoO. Heating of these solids at temperatures varying between 900 and 1100°C led also to the formation of a new lithium oxide cobaltic oxide phase, the composition of which has not yet been identified. The role of Li 2O in increasing the thermal stability of Co 3O 4 was attributed to the substitution of some of its cobalt ions by Li + ions, according to Verwey and De Boer's mechanism, leading to the transformation of some of the Co 2+ into Co 3+ ions thus increasing the oxidation state of the cobaltic oxide lattice.