Ordered deficent perovskite La_2/3TiO₃ grown via molecular beam epitaxy

Molecular beam epitaxy growth of the ordered deficient perovskite La_2/3TiO₃ has been achieved. Grown as an epitaxial film, La_2/3TiO₃ has well-defined domains over chip-sized area: it appeals as a "parent compound" into which ions can be electrochemically inserted. A-site vacancy ordering can occur along a pseudocubic perovskite axis, such that planes of the crystal normal to the axis have stoichiometries of LaO, TiO₂, and notably La_1/3O. Here, we achieve ordering by a cooling-and-annealing growth method, monitored in situ by reflection high-energy electron diffraction. Ordering normal to the film surface is revealed by X-ray diffraction; ordering in the plane of the film surface is also suggested by reflection high-energy electron diffraction. The La_1/3O layers in the ordered La_2/3TiO₃ film may act as conduction channels for the transport of inserted ions, as suggested by the high ionic conductivity of a promising solid state electrolyte Li_3xLa_2/3-xTiO₃; with controlled lithium insertion, probing the phase diagram of the mixed valence system Li_xLa_2/3Ti³⁺_xTi⁴⁺_1-xO₃ can give rise to new iontronics.