Crystal Structure of Barium Titanate

IT is well known that barium titanate belongs to the group of compounds having structures of the perovskite type¹. The ideal perovskite structure (G5 in the ``Strukturbericht'') has a simple cubic lattice, with one formula-weight per cell, the atomic parameters being as follows: 2-valent cation, (0,0,0); 4-valent cation, (½,½,½) ; oxygens, (0,½,½), (½,0,½), (½,½,0). It was early recognized² that for many of these compounds, including perovskite (CaTiO₃) itself as well as barium titanate, the structure was not truly cubic, but was actually a slightly deformed modification of it. Perovskite itself is generally believed monoclinic; the structure has recently been determined in detail by Naray-Szabo³, who finds a monoclinic unit cell with all its edges doubled relative to the unit cell of the ideal structure. No detailed work on barium titanate has hitherto been published, and it was thought of interest to investigate it. Powder photographs of the synthetic material taken in a 19 cm.-diameter camera with copper Kα radiation provided the data for determining the structure.