Calcium-free double-layered cuprate superconductors with critical temperature above 100 K

Abstract

AbstractCalcium is a vital constituent in multilayered cuprate superconductors with critical temperatures (Tc) above 100 K, because it plays a key role in separating CuO2 planes. Here, we demonstrate the synthesis of calcium-free double-layered cuprates: Sr2SrCu2O4(X,O)2(X = F, Cl, and Br) and M(Sr,Ba)2SrCu2Oy(M = Hg/Re, Tl, and B/C), where strontium exists between the CuO2 planes. Oxyfluoride and mercury-based materials show a Tc of 107 K and 110 K, respectively, which are high compared to existing calcium-free cuprates. These findings indicate Tc greater than 100 K can be realized by replacing both barium and calcium, which have been indispensable in conventional multilayered cuprates, with strontium. Furthermore, the non-toxicity of Sr2SrCu2O4F2 and (B,C)Sr2SrCu2Oy simplifies the synthesis process and ensures their safety in potential applications. We also perform a comparison of the characteristic structural parameters between the calcium-free and calcium-containing cuprates considering the number of CuO2 planes.