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

Lii-Cherng Leu, Boise State University
Jianjiang Bian, Shanghai University
Delphine Gout, Oak Ridge National Laboratory
Steve Letourneau, Boise State University
Rick Ubic, Boise State University

Abstract

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 < 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 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.