Temperature-dependent structural transformations of hydrothermally synthesized cubic Li2TiO3 studied by in-situ neutron diffraction

The structural changes of hydrothermally synthesized cubic Li2TiO3 were studied in-situ during heating and cooling at the neutron powder diffractometer SPODI at FRM II, Caching. The initially cubic (Fm (3) over barm) phase shows a slight Li deficit, but becomes stoichiometric with increasing temperature. It transforms to a monoclinic (C2/c) structure above 300 degrees C and back to the same cubic (Fm (3) over barm) structure at 1155 degrees C. A two-phase region is observed between 300 and 500 degrees C, indicating a first order character of the transformation. Below 1000 degrees C, during the first heating, the monoclinic Li2TiO3 phase is disordered due to stacking faults. Between 1160 and 1140 degrees C, the cubic phase becomes monoclinic again upon cooling and stays well ordered down to room temperature. Anomalies in the thermal expansion of the monoclinic modification occur at around 600 degrees C for both, heating and cooling. These are assigned to strains building up during the first phase transformation upon heating and the confinement in the compacted ceramic sample during cooling, respectively.