Structural investigations of migration pathways in lithium ion-conducting La2/3−Li3TiO3 perovskites

Local structure of the Li1/8La5/8TiO3(LLTO) ionic conductor by theoretical simulations

“…It was confirmed that by X-ray diffraction the superlattice peaks transforming a p ×a p ×2a p into √2a p ×√2a p ×2a p are missed completely. Another investigation, carried out on the x=0.36 composition, proposed instead an orthorhombic Cmmm structure similar to that found for Li-poor terms [11].…”

“…For model (ii), Li is located very close to site S3 at the window centre. Sites S1 and S3 are the most relevant ones for the process of Li + ion transfer involved in ionic conductivity [9][10][11]16,21]. The experimental structural studies of Li 0.16 La 0.613 TiO 3 [7] and Li 0.18 La 0.607 TiO 3 [8] show Li in slightly displaced positions.…”

“…Clearly, the extended disordered distribution of lithium atoms and vacancies is responsible for the high ionic mobility. However, although several structural studies of this system at a number of Li compositions have been performed, only in a few cases lithium could be located and/or refined by neutron diffraction [5][6][7][8][9][10][11]. This task is particularly difficult in case of small Li content (say, x < 0.25), where a problem of scattering sensitivity arises.…”

“…First, a partial ordering of the La-Li-substitution in the A cages is observed along the z axis; this makes the c cell edge to double from a p to 2a p , so that alternate (001) layers of La-rich and La-poor Atype sites arise. Second, the TiO 6 octahedra tilt in anti-phase sequence around at least one of the crystallographic axes, which is z for tetragonal structures [9,10] (a 0 a 0 c -scheme, according to Glazer's notation [12]), and usually y for orthorhombic structures [7,8,11] (a 0 b -c 0 scheme). An enlargement of the unit-cell in the (001) plane from a p ×a p to √2a p ×√2a p (tetragonal) or to 2a p ×2a p (orthorhombic) ensues.…”

On the Power Law Behavior of the A.C. Conductivity in Li Ion Conducting Perovskites

“…Many approaches have been developed to explain such behavior. Among these, the average valence of the A-site cation 17,27) , and the dimensionality of ion transport pathways 3,28) .…”