An investigation into the temperature phase transitions of synthesized lithium titanate materials doped with Al, Co, Ni and Mg by in situ powder X-ray diffraction

Abstract

Li4Ti5O12 (LTO) and its doped analogues Li4Ti4.95M0.05O12 (M = Al3+, Co3+, Ni2+, and Mg2+) were synthesized and characterized using in situ PXRD to monitor the phase transitions during the sol–gel synthesis of the spinel material. These results are complimented by thermogravimetric analysis, which illustrates the decomposition of the materials synthesized, where the final LTO products are seen to form at approximately 550 °C. The material has an amorphous structure from room temperature, coupled with a crystalline phase which is speculated to be H2Ti2O5·H2O. This crystalline phase disappears at 250 °C, with the material still in the amorphous state. The crystalline LTO phase starts at approximately 550 °C, with anatase co-crystallizing with the spinel phase. Rutile appears at 600 °C and co-crystallizes with the final product at 850 °C, where anatase is no longer seen. The rutile impurity remains present after cooling the material to room temperature, and results indicate that prolonged heating at 850 °C is required to reduce the rutile content. Rietveld refinement of diffraction patterns show that the unit-cell parameter increases with increasing temperature, coupled with a decrease when cooling the sample. The crystallite sizes follow the same trend, with a significant increase above temperatures of 750 °C.