Molecular layer-by-layer engineering of superconducting and superionic materials in the (AgI)Bi₂Sr₂CaCu₂O_y system

We have developed a new interstratified system consisting of a superconducting layer alternating with a superionic conducting one, which is the AgI intercalated Bi₂Sr₂CaCu₂O_y with well-defined 2-dimensional heterostructure. Before and after the intercalation of AgI, the superconducting properties remained unchanged with the T_c's of 76 K for the pristine and 63 K for the intercalate. From the extended X-ray absorption fine structure spectroscopic analysis, it is found that the intercalated AgI is formed as the β-like intracrystalline structure in the 2-dimensional interlayer space of Bi₂Sr₂CaCu₂O_y. According to the ac impedance and dc relaxation measurements, the ionic transference number (t_i = σ_i/σ_r) has been estimated to be 0.27 (at 167°C), indicating that the substantial ionic conductivity (σ₁) contributes to the total electrical one (σ_T). In comparison of the ionic conductivity for (AgI)Bi₂Sr₂CaCu₂O_y (σ_i ≈ 10^-3-10^-23 Ω^-1 cm^-1) with those for the well-known superionic conductors of cation-substituted β-aluminas, the ionic transport in (AgI)Bi₂Sr₂-CaCu₂O_y turned out to be significant, even comparable with the superionic conductors.