Phase Changes in Li2Ti3O7

The ramsdellite phase (R), Li2Ti3O7, was synthesized by the melt-quenching method and its phase changes were investigated by thermal analyses (TG-DTA, TMA), powder X-ray diffractometry, and scanning electron microscopy. In the heating process, the R phase transformed into a hexagonal phase (H) followed by decomposition into Li4Ti5O12 (spinel phase=S) and TiO2 (rutile phase=r), and finally, the R phase was reproduced. This reaction path agreed well with that reported by Mikkelsen, but each reaction temperature differed from that, and the single phase region for the H phase was not detected. The rate-determining step for the R->H transformation was the nucleation of the H phase. An abnormal change of the order of 10-3K-1 in the thermal expansion coefficient was observed at -630°C, which is attributed mainly to the formation of cracks accompanied by the transformation from R to H phase. In the cooling process, the R phase transformed into an H phase followed by the successive decomposition into the S and r phases, taking the same phase change path as in the heating process.