Order-Disorder Transition in the (1−x)Li₂TiO₃–xMgO System (0 ≤ x ≤ 0.5)

The order–disorder phase transition of magnesium lithium titanate solid–solution (1− x )Li ₂ TiO ₃ – x MgO (0 ≤ x ≤ 0.5) ceramics prepared by conventional solid-state processing has been examined. The phase and structural analysis was carried out using electron diffraction, neutron diffraction and high-resolution transmission electron microscopy. Both electron and neutron diffraction results revealed the onset of an order-to-disorder transition at 0.3 < x < 0.4. Superlattice reflections found in certain regions of x = 0.2 samples and most areas of x = 0.3 samples were caused by a twin structure stabilized by Mg incorporation. Rietveld refinements of neutron diffraction data suggested a random distribution of Mg on the Li 4 e sites and equal distribution of Mg on the two Ti 4 e sites for x ≤ 0.3. As the Mg content continues to increase, the crystal symmetry transforms from monoclinic to cubic rocksalt. Consequently, the cation ordering on the 8 f and 4 d sites of the C 2/ c structure became corrupted and turned into short-range ordering on the 4 a sites of a cubic structure with symmetry, resulting in diffuse scattering in electron diffraction patterns.