Order-Disorder Transition in the (1−\u3cem\u3ex\u3c/em\u3e)Li\u3csub\u3e2\u3c/sub\u3eTiO\u3csub\u3e3\u3c/sub\u3e–\u3cem\u3ex\u3c/em\u3eMgO System (0 ≤ \u3cem\u3ex\u3c/em\u3e ≤ 0.5)

The order–disorder phase transition of magnesium lithium titanate solid–solution (1−x)Li2TiO3–xMgO (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 \u3c x \u3c 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 4e sites and equal distribution of Mg on the two Ti 4e 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 8f and 4d sites of the C2/c structure became corrupted and turned into short-range ordering on the 4a sites of a cubic structure with symmetry, resulting in diffuse scattering in electron diffraction patterns