Effect of Nb2O5 Addition on the Phase Change in Li2Ti3O7

Nb2O5-added R (ramsdellite) phase was syntbesized by the melt-quenching method. Addition of 3 to 5mol% Nb2O5 accelerated the R->H (hexagonal phase) transformation, retarded the H->S+r (spinel and rutile) successive decomosition reaction, and stabilized the H phase at high temperatures. These effects were possibly caused by the preferential incorporation of Nb2O5 in the H phase. The phase changes in the Nb2O5-added R phase occurred similarly to the non-added R phase following the route quenched-R->H->S+r->R during heating and R->H->S+r during cooling, respectively. The R phase containing 3mol% Nb2O5 was heated to 850°C at 2°C/min in air, then quenched, and the H phase was obtained although very small amounts of rutile and spinal were contained. Lattice constants of the obtained H phase were a=0.8777(8)nm and c=6.988(2)nm, and the effect of Nb2O5 addition was hardly recognized. The linear thermal expansion coefficient of the H phase was determined to be α=1.34×10-5K-1 between room temperature and 900°C. Investigation on the phase changes in the H phase during heating clarified those in the R phase.