Ba(1-x)Na(x)Ti2Sb2O (0.0 ≤ x ≤ 0.33): a layered titanium-based pnictide oxide superconductor

A new layered Ti-based pnictide oxide superconductor, Ba(1-x)Na(x)Ti(2)Sb(2)O (0.0 ≤ x ≤ 0.33), is reported. X-ray studies revealed that it crystallizes in the tetragonal CeCr(2)Si(2)C structure. The undoped parent compound, BaTi(2)Sb(2)O [P4/mmm; a = 4.1196(1) Å; c = 8.0951(2) Å], exhibits a charge density wave (CDW)/spin density wave (SDW) transition at 54 K. Upon chemical doping with Na, the CDW/SDW transition is systematically suppressed, and superconductivity arises with the critical temperature (T(c)) increasing to 5.5 K. Bulk superconductivity was confirmed by resistivity, magnetic, and heat capacity measurements. Like the high-T(c) cuprates and the iron pnictides, the superconductivity in BaTi(2)Sb(2)O arises from an ordered state. Similarities and differences between BaTi(2)Sb(2)O and the cuprate and iron pnictide superconductors are discussed.