Structure for perovskites with layered ordering of A-site cations.

The structure of La(1/3)NbO3 is that of a perovskite with La3+ cations ordered into alternate layers of perovskite A-sites. This is the description of a tetragonal structure and yet the room-temperature structure shows an orthorhombic distortion. The structure of La(2/3)TiO3 shows similar features. It has been recognized only very recently that the orthorhombic distortion in both these compounds is due to octahedral tilting. It seems clear from the literature that Ce(2/3)TiO3, Pr(2/3)TiO3, Nd(2/3)TiO3 and Ce(1/3)NbO3 adopt the same structure. Structures of other perovskites, such as Ln(2/3)TiO3, Ln(1/3)NbO3 and Ln(1/3)TaO3 (Ln = lanthanoid), when orthorhombically distorted, may be similar.