The cobaltite Ca 3Co 4O 9+δ has shown large thermopower and is considered to be a good candidate for use as a thermoelectric material. The composition of Ca 3Co 4O 9+δ is better expressed as [Ca 2CoO 3][CoO 2] b1/b2 with the misfit-layered structure featuring different periodicities along the b axis, with b 1 referring to the b-axis length of the NaCl-type [Ca 2CoO 3] sublattice and b 2 referring to the b-axis length of the [CoO 2] sublattice. The crystal structure of Ca 3Co 4O 9+δ can be viewed as being of two subsystems, i.e., the distorted NaCl-type [Ca 2CoO 3] sublattice and the CdI 2-type [CoO 2] sublattice, alternately stacked along the c-axis. In this paper, we report measurements of the electrical resistivity and Seebeck coefficient for a series of misfit-layered oxides Ca 3Co 4-x Si x O 9+δ prepared by solid-state reaction. Structural parameters are refined with the superspace group X2/m(0β0)s0 using powder x-ray diffraction data. With partial substitution of Si 4+ for Co 3+, the resistivity decreases, while the thermopower increases simultaneously. These results indicate that partial substitution of Si 4+ improves the thermoelectric characteristics of Ca 3Co 4O 9+δ .
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering
- Materials Chemistry