High ionic conductivity in lithium lanthanum titanate

It has been discovered that the polycrystalline lithium lanthanum titanate Li0.34(1)La0.51(1)TiO2.94(2) shows high ionic conductivity more than 2 × 10−5 S cm−1 (D.C. method) at room temperature, which is compared with that of Li3.5V0.5Ge0.5O4. This compound has cubic perovskite structure whose cell parameter is 3.8710(2) A. By a.c. impedance analysis, the equivalent circuit of the sample could be divided into two parts; bulk crystal and grain boundary. The ionic conductivity of the bulk part is as high as 1 × 10−3 S cm−1 at room temperature. Such a high conductivity is considered to be attributed to the presence of a lot of equivalent sites for lithium ion to occupy and freely move in this perovskite. In addition, this compound is easy to react with lithium metal and the electronic conductivity has become much higher than before being in contact with Li. It can be explained that titanium ion was reduced by ii insertion into a vacant site and then an electron carrier was introduced.