Relation between Seebeck Coefficient and Lattice Parameters of (Ca2-ySryCoO3)(x)CoO2

Abstract

The effect of dopant content on the Seebeck coefficient of the Sr2+-doped (Ca2- Sr CoO3) CoO2 ( = 0 to 0.4) system was investigated. This system can be described as a misfit layered structure of (CoO2) and (Ca2- Sr CoO3) layers, which have different lattice parameters denoted by (1) and (2), respectively. Due to the solubility limit of Sr in (Ca2CoO3) CoO2, systematic investigations were available only up to = 0.2. Nevertheless, the structural uniqueness enabled partially quantitative analysis of the correlation between the crystal structure and Seebeck coefficient of the system. Substitution of Sr for Ca leads to lattice expansion which accompanies an anisotropic change of the lattice parameters. Among the lattice parameters considered, the increase in the lattice parameter (2) of the insulating layer was larger than the change of any other lattice parameter, which induced in-plane stress in the conducting layer. As a result, as the (1)/ (2) misfit ratio of (Ca2- Sr CoO3) CoO2 is decreased, the Seebeck coefficient also decreases. Practical guidance for selecting dopants to enhance thermoelectric performance is proposed.