HRTEM and micro-raman studies on superconducting-superionic conducting nanohybrid, Ag_1.17I_1.54Bi₂Sr₂CaCu ₂O_y

The crystal structure of the superconducting-superionic conducting nanohybrid, Ag_1.17I_1.54Bi₂Sr₂CaCu ₂O_y, has been investigated by performing high-resolution transmission electron microscopy (HRTEM) and micro-Raman spectroscopy. From the HRTEM image along the [110] direction, it is found that a hexagonal-like array of AgI₄ tetrahedra is stabilized between each [Bi-O]₂ double layer with a staggered configuration of host block. The two-dimensionally extended Ag-I sublattice provides a favorable migration path for Ag⁺ ions that is consistent with high ionic conductivity of the Ag-I intercalate. According to the polarized micro-Raman spectroscopy, the doubly split O_Sr phonon line is collapsed into a single one upon Ag-I intercalation, as observed in the phase of IBi₂Sr₂CaCu₂O_y. Such an evolution of the O_Sr phonon peak is surely attributed to a weakening of the O_Bi-Bi-O_Sr coupling due to the remarkable lattice expansion, which is in good agreement with the HRTEM result.