Two Superconducting Phases and Their Characteristics in Layered BaTi₂(Sb_1?xBi_x)₂O with x=0.16

Two correlated superconducting phases are identified in the layered superconductor BaTi₂(Sb_1?xBi_x)₂O (x=0.16), with the superconducting transition temperatures of T_C=6 K (the high T_C phase) and 3.4 K (the low T_C Phase), respectively. The 6 K superconducting phase appears first in the as-prepared sample and can decay into the low T_C phase by exposure to an ambient atmosphere for a certain duration. Specially, the high T_C phase can reappear from the decayed sample with the low T_C phase by vacuum annealing. It is also found that the CDW/SDW order occurs only with the 6 K superconducting phase. These notable features and alteration of the superconductivity due to the post-processing and external pressure can be explained by the scenario of electronic phase separation.