Low temperature structural changes of complex ferroelectric La2Ti2O7

La2Ti2O7 is part of an intriguing family of layered perovskite-related materials which display an unusual type of ferroelectricity. In contrast to standard ABO3 perovskites (in which octahedral rotations alone are non-polar) the ferroelectricity in La2Ti2O7 and relatives can be driven solely by rotations and tilts of the TiO6 octahedra. However, the crystal structures of these materials are very complex and we have uncovered evidence which suggests that the currently assigned space group is incorrect. Therefore, we propose to perform a detailed structural study of La2Ti2O7 to low temperature to confirm the ambient temperature space group and characterise its structural behaviour to low temperature with the aid of symmetry mode analysis with the goal of better understanding its ferroelectricity. This will also be of importance for the wider material class which is currently under-studied.