Neutron Diffraction Study of Quenched Li0.3La0.567TiO3 Lithium Ion Conducting Perovskite

Abstract

The Li+ ion conductor Li0.3La0.567TiO3 was synthesized as a metastable phase quenched in liquid N2 from 1300 °C, and it was studied by time-of-flight powder neutron diffraction at high-resolution (HRPD instrument, ISIS Facility, U.K.). At room temperature a tetragonal perovskite superstructure was found, with a √2ap × √2ap × 2ap unit cell (a = 5.48027(1), c = 7.75591(2) A, and Z = 4), I4/mcm space group, and a0a0c- tilt system of the TiO6 octahedra. Superlattice hkl reflections with odd l were systematically weaker and broader. By Fourier difference maps, the Li atom was located in a disordered position inside the La vacancy hollow, close to the bottleneck site at the center of the Ti4O4 square window. The Rietveld refinement converged to Rp = 6.56%, RBragg(even l) = 3.26%, and RBragg(odd l) = 11.6%. A two-dimensional pathway of Li+ ion mobility inside the structure, based on the coupled ordering of lithium and lanthanum, is proposed. At about 600 °C the unit cell transforms into ap × ap × ap, with a disa...