Electrical properties of Ca_3–xSm_xCo₄O_9+δ ceramics prepared under magnetic field

We fabricate Sm-doped Ca₃Co₄O_9+δ (CCO) bulk materials in magnetic field during both processes of chemical synthesis and cold pressing. The structure and electrical performance of the samples are investigated. With the increasing Sm concentration, the electrical conductivity 1/ρ decreases and the Seebeck coefficient α increases. As a result, the power factor (PF = α ²/ρ) is raised slightly. After applying magnetic field, the extent of texture, grain size and density of all the bulk materials are improved obviously, thereby an enhanced electrical conductivity can be gained. Additionally, the degeneracy of Co⁴⁺ state in the CoO₂ layer of CCO is also increased as the magnetic field is used in the preparing process, which results in an enhanced α. The Ca_2.85Sm_0.15Co₄O_9+δ prepared in magnetic field shows the largest power factor (0.20 mW⋅m⁻¹⋅K⁻² at 1073 K). (paper)