| Abstract
| - The parent phase of misfit-layered cobalt oxides forms in the ternary Sr−Co−O system: the new phase possesses a three-layer crystal structure, SrO−SrO−CoO2, and a chemical formula, [Sr2O2]qCoO2, in which the “misfit parameter” q is 0.5, i.e., the phase is commensurate.
- Misfit-layered (ML) cobalt oxides of the general formula of [MmA2Om+2]qCoO2 have been proven tobe efficient thermoelectric materials because the structure is capable in accommodating the two seeminglycontradictory characteristics of high electrical conductivity and large thermoelectric power. They arealso potential hosts for other oxymoron-like functions. The known phases all contain one or two square-planar MO (M = Co, Bi, Pb, Tl, etc.) layers sandwiched together with two AO (A = Ca, Sr, Ba, etc.)planes of square symmetry between two adjacent CoO2 layers of hexagonal symmetry. Here, we reportthe realization of the simplest (m = 0) ML phase forming in the Sr−Co−O system with the cation ratioSr/Co = 1. Atomic-resolution transmission electron microscopy (TEM) imaging confirms for the newphase the parent three-layer crystal structure, SrO−SrO−CoO2, which is compatible with the formula of[Sr2O2]qCoO2. Electron diffraction reveals that the phase is rather commensurate, i.e. the “misfit parameter”q is 0.5. Nevertheless, in terms of the transport-property characteristics, the new ML parent is comparableto its earlier-established and more-complex derivatives.
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