Temperature-dependent structural transformations of hydrothermally synthesized cubic Li2TiO3studied byin-situneutron diffraction

Abstract

AbstractThe structural changes of hydrothermally synthesized cubic Li2TiO3were studiedin-situduring heating and cooling at the neutron powder diffractometer SPODI at FRM II, Garching. The initially cubic (Fm-3m) phase shows a slight Li deficit, but becomes stoichiometric with increasing temperature. It transforms to a monoclinic (C2/c) structure above 300 °C and back to the same cubic (Fm-3m) structure at 1155 °C. A two-phase region is observed between 300 and 500 °C, indicating a first order character of the transformation. Below 1000 °C, during the first heating, the monoclinic Li2TiO3phase is disordered due to stacking faults. Between 1160 and 1140 °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 °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.