Temperature-dependent structural transformations of hydrothermally synthesized cubic Li₂TiO₃studied by<i>in-situ</i>neutron diffraction

Abstract

Abstract The structural changes of hydrothermally synthesized cubic Li 2 TiO 3 were studied in-situ during heating and cooling at the neutron powder diffractometer SPODI at FRM II, Garching. The initially cubic ( Fm -3 m ) phase shows a slight Li deficit, but becomes stoichiometric with increasing temperature. It transforms to a monoclinic ( C 2/ c ) structure above 300 °C and back to the same cubic ( Fm -3 m ) 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 Li 2 TiO 3 phase 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.