HEBM synthesis of nanocrystalline LiZn0.5Ti1.5O4 spinel and thermally induced order-disorder phase transition (P4332→Fd3¯m)

Nanocrystalline LiZn0.5Ti1.5O4 disordered spinel (S.G. Fd3¯m) was synthesized by high energy ball milling (HEBM). TEM analysis of the sample has shown that the particle size distribution is broad ranging from 10 to 60 nm. By X-ray line broadening analysis, the average apparent size of the crystallites is found to be 19(1) nm, while the average apparent strain is 26(4) × 10−4. The cation distribution was found to be metastable, with Zn in octahedral 16d and Ti in tetrahedral 8a position, against their known site preference. After annealing the sample at 650 °C for 3 h and slow cooling down to room temperature, superstructure reflections (1 1 0), (2 1 0), (2 1 1) have been observed, indicating a cation ordering in the octahedral sublattice and a combined symmetry reduction (S.G. P4332). The reverse symmetry change P4332→Fd3¯m caused by increasing the temperature was studied by in situ XRPD, DSC/DTA, Landau's theory of phase transitions and Raman spectroscopy. An analysis of the topology of the order parameter vector space indicates a biquadratic or linear-quadratic coupling between the order parameters Q1 and Q2. In LiZn0.5Ti1.5O4 dilatation expansion of crystal lattice as well as spontaneous strain values are rather small (order of 10−4), comparing to e.g. Li1.33xCo2−2xTi1+0.67xO4.