Reactivity and stability of rare earth oxide–Li2CO3 mixtures

The thermal stability of a mixture of Li2CO3 and rare earth oxide (R2O3) was examined under a dry condition. The heat-treatment of the mixture in CO2 ambience resulted in the formation of rare earth carbonates for R = La, Pr, Nd, Sm, Eu, and Gd except for Ho–Lu and Y. Lithiation of their rare earth dioxymonocarbonate, i.e., R2O2+2x(CO3)1−xLi2x was confirmed for R = La, Pr, Nd, and Sm when the mixture was heated at 900 °C. The lithiation degree, x, was increased with an increase in the heat-treatment temperature in CO2 and was lower than 0.3. The stability of lithium rare earth dioxymonocarbonate decreased with the atomic number of the rare earth. The high reactivity of the light rare earth oxides with Li2CO3 would be attributed to that the large R3+–O2− distance for CN = 5 and 6 with an increase in the ionic [R3+]/[O2−] ratio for the rare earth oxides and is very similar with that of the rare earth dioxymonocarbonates.