Structural Channels and Atomic-Cluster Insertion in Cs_xBi₄Te₆ (1 ≤ x ≤ 1.25) As Observed by Aberration-Corrected...

Microstructural analyses based on aberration-corrected scanning transmission electron microscopy (STEM) observations demonstrate that low-dimensional Cs_xBi₄Te₆ materials, known to be a novel thermoelectric and superconducting system, contain notable structural channels that go directly along the b axis, which can be partially filled by atom clusters depending on the thermal treatment process. We successfully prepared two series of Cs_xBi₄Te₆ single-crystalline samples using two different sintering processes. The Cs_xBi₄Te₆ samples prepared using an air-quenching method show superconductivity at approximately 4 K, while the Cs_xBi₄Te₆ with the same nominal compositions prepared by slowly cooling are nonsuperconductors. Moreover, atomic structural investigations of typical samples reveal that the structural channels are often empty in superconducting materials; thus, we can represent the superconducting phase as Cs_1-yBi₄Te₆ with considering the point defects in the Cs layers. In addition, the channels in the nonsuperconducting crystals are commonly partially occupied by triplet Bi clusters. Moreover, the average structures for these two phases are also different in their monoclinic angles (β), which are estimated to be 102.3° for superconductors and 100.5° for nonsuperconductors.