The electrical properties of Ca0.33CoO2 epitaxial films are investigated as the Ca2+-arrangement is transformed. Despite identical Ca-content, annealing the film caused the Ca-arrangement to change from a <!-Math-> hexagonal type to a 2a × <!-Math-> orthorhombic type, which was confirmed by X-ray diffraction and scanning transmission electron microscopy. A hexagonal Ca-arrangement type, Ca 0.33CoO2, exhibited a metallic resistivity as low as 7.5 × 10-4 Ω·cm and a moderately large thermopower (̃100μV·K-1), whereas the orthorhombic Ca-arrangement type displayed a thermally-activated resistivity (10-2 Ω·cm) with a slightly increase in thermopower, which led to about a one order of magnitude difference in the thermoelectric power factor.
ASJC Scopus subject areas
- Physics and Astronomy(all)