Tc Enhancement by Aliovalent Anionic Substitution in Superconducting BaTi2(Sb1-xSnx)2O

BaTi2Sb2O is a T-c = 1.2 K superconductor with a d(1) square lattice, and isovalent Bi substitution for Sb can increase its T-c to 4.6 K (BaTi2Bi2O), accompanied by the complete suppression of charge density wave (CDW) or spin density wave (SDW) transition. In the present study, we demonstrate that aliovalent Sn substitution (hole doping) also increases T-c up to 2.5 K for BaTi2(Sb0.7Sn0.3)(2)O, while suppressing CDW/SDW transition only slightly. The overall electronic phase diagram of BaTi2(Sb, Sn)(2)O is qualitatively similar to that of cation-substituted (hole-doped) (Ba,Na)Ti2Sb2O, but quantitative differences such as in T-c are observed, which is discussed in terms of Ti-Pn hybridization and chemical disorder.