Superionic and Superconducting Nanohybrids with Heterostructure, Ag_xI_wBi₂Sr₂Ca_n-1Cu_nO_y(0.76 ≤x≤ 1.17,n= 1, 2, and 3)

Abstract

New mixed conducting hybrid systems, AgxIwBi2Sr2Can-1CunOy (n = 1, 2, and 3), have been developed successfully by intercalating the superionic conducting Ag−I layer into the superconducting Bi2Sr2Can-1CunOy lattice. Although the Ag−I intercalation gives rise to a remarkable basal increment of ∼7.3 Å, which is twice as large as that of the iodine intercalate (Δd = 3.6 Å), it has little influence on the superconducting property with only a slight Tc depression. Systematic X-ray absorption near edge structure (XANES)/extended X-ray absorption fine structure (EXAFS) studies clearly reveal the charge transfer between host and guest, indicating that a change in hole concentration of the CuO2 layer is the main origin of Tc evolution upon intercalation. According to the ac impedance and dc relaxation analyses, the AgxIwBi2Sr2Can-1CunOy compounds possess fast ionic conductivities (σi = 10-1.4−10-2.6 Ω-1 cm-1 at 270 °C) with the activation energies of 0.22 ± 0.02 eV, which are similar to those of other two-dimensional Ag+ superionic conductors. A more interesting finding is that these intercalates exhibit both high electronic and ionic conductivities with ionic transference numbers of ti = 0.02−0.60, due to their interstratified heterostructures consisting of a superionic conducting silver iodide layer and a metallic host layer. A close relationship between local crystal structure and ionic conductivity has been elucidated from the detailed Ag K-edge EXAFS analyses, where a reasonable pathway for Ag+ ionic conduction is suggested along with the intracrystalline structure of the Ag−I sublattice.