Two superconducting phases and their characteristics in layered BaTi2(Sb1-xBix)2O with x=0.16

Two correlated superconducting phases are identified in layered superconductor BaTi2(Sb1-xBix)2O (x=0.16), with the superconducting transition temperatures of TC = 6 K (the high TC phase) and 3.4 K (the low TC Phase), respectively. The 6 K superconducting phase appears firstly in the as-prepared sample and can decay into the low TC phase by exposing to ambient atmosphere for certain duration. Especially the high TC phase can reappear from the decayed sample with the low TC 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 superconductivity due to the post-processing and external pressure can be explained by the scenario of electronic phase-separation.