It was noted that the cuspidine system, La4(Ti2−xGaxO8−x/2)O2 had recently been shown to display significant oxide ion conductivity at elevated temperatures, with evidence for proton conduction at low temperatures in wet atmospheres. A computer model study was made of the La4(Ti2O8)O2 (x = 0) end-member. In agreement with experimental studies, the most favourable oxide ion vacancy defect was found at the bridging-O position (O3). Oxide ion migration was shown to proceed via a cooperative vacancy migration process with a calculated activation energy of 1.51eV, in very good agreement with experiment. The computational results for water incorporation suggest that O vacancies were required for water incorporation to occur, which also agrees with experiment, and the most favourable position for the proton was the bridging oxygen (O3).

A Computational Study of Oxide Ion Migration and Water Incorporation in the Cuspidine System, La4(Ti2O8)O2. E.Kendrick, M.Russ, P.R.Slater: Solid State Ionics, 2008, 179[21-26], 819-22