The atomic positions of ferroelectric BaTi${\mathrm{O}}_3$ in its orthorhombic phase have been determined by a singlecrystal neutron diffraction analysis. Pillar-shaped crystals with their major axes along the cubic [110] direction were maintained as single domains by the application of an electric field. The structure deduced can be viewed as a framework of slightly distorted oxygen octahedra, in which the central Ti ions are displaced towards one of the octahedron edges (polar axis) by 0.13 A. The Ba ions are also shifted in the same direction but by the smaller amount of 0.07 A. A comparison of this structure with that of the tetragonal phase suggests the essential role of Ti in the ferroelectricity of this crystal as treated by Slater.

• Received 22 October 1956

DOI:https://doi.org/10.1103/PhysRev.105.856