Abstract
Our ability to directly characterize the atomic and electronic structures is crucial to developing a fundamental understanding of structure-property relationships in complex-oxide materials. Here, we examine one specific example, the misfit-layered thermoelectric material CaCoO, which exhibits a high Seebeck coefficient governed by spin-entropy transport as well as hopping-mediated electron transport. However, the role of oxygen and its bonding with cobalt in thermoelectric transport remains unclear. We use atomic-resolution annular bright-field imaging to directly image the oxygen sublattice and to combine our experimental data with multislice image calculations to find that the oxygen atoms in the CoO subsystem are highly ordered, while the oxygen-atomic columns are displaced in the CaCoO subsystem. Atomic-column-resolved electron energy-loss spectroscopy and spectrum image calculations are used to quantify the bonding in the different subsystems of incommensurate CaCoO. We find that the holes in the CoO subsystem are delocalized, which could be responsible for the -type conductivity found in the CoO subsystem.
2 More- Received 16 November 2011
DOI:https://doi.org/10.1103/PhysRevB.85.054106
©2012 American Physical Society