Synthesis, structure and physical properties of reduced barium titanate Ba2Ti13O22

Polycrystalline sample of the reduced barium titanate Ba2Ti13O22 was synthesized by solid state reaction at 1523 K in Ar atmosphere for the first time. The Rietveld refinement using the powder X-ray diffraction data confirmed the sample to be main phase of Ba2Ti13O22 having the orthorhombic crystal system, space group Bmab and the lattice parameters of a=11.67058(11) Å, b=14.12020(13) Å and c=10.06121(9) Å, and V=1657.995(20) Å3. The valence state of Ti was evaluated by both the Ti–O bond distance analysis and the Ti K-edge XANES analysis. The magnetic susceptibility was nearly temperature independent in the range of 60–300 K, suggesting the Van Vleck Paramagnetism. The electrical conductivity at 300 K is approximately 320.50 S/cm, and a semiconducting behavior was observed below room temperature. The Seebeck coefficient showed a negative value of −1.25 μV/K at 300 K, indicating n-type behavior. These facts were confirmed by the results of the present theoretical calculations by the FLAPW method.