Superconductivity in the Hypervalent Compound Ba2Bi(Sb1-xBix)2 with a Square-Honeycomb Lattice

We studied the structural and physical properties of the hypervalent system Ba2Bi(Sb1-xBix)(2) (0 <= x <= 1) with an anisotropic square-honeycomb layer. We found that the orthorhombic Ba2BiSb2 (x = 0) shows a charge density wave (CDW) transition at approximately 230K accompanied by a significant elongation of the b-axis, indicating the quasione- dimensional nature along the b-axis in its electronic state, as supported by first-principles calculations. This CDW transition is rapidly suppressed with increasing x, leading to the appearance of superconductivity for 0.375 <= x <= 1. The superconducting transition temperature T-c increases slightly with x and the maximum T-c was 4.4K for Ba2Bi3 (x = 1).