Synthesis and Crystal Structure of Ba2Ti13O22: A Reduced Form of BaTi5O11 by the Titanium Insertion

A new member of barium titanate compounds Ba2Ti13O22 was synthesized by the reaction of BaTiO3, Ti2O3, and TiO at 1853 K in an argon atmosphere. It crystallizes in the orthorhombic system, space group Bmab , a = 11.6550(8) Å, b = 14.1062(8) Å, c = 10.0535(9) Å, V = 1652.9(2) Å3, and Z = 4. The structure was determined from a single-crystal X-ray diffraction study and refined to the conventional values of R = 0.055 and wR = 0.043 for 2050 observed reflections. The closest packing structure of Ba and O atoms in Ba2Ti13O22 is identical with that in the BaTi5O11 structure. The vacant octahedral O6 interstices in BaTi5O11 are completely occupied by the additional titanium cations in the present Ba2Ti13O22, and the face-sharing Ti2O9 double group with a short Ti-Ti distance of 2.730(2) Å is formed as in the hexagonal BaTiO3 structure.