Thermoelectric properties of grain-aligned Ca-based cobaltites by a magneto-scientific method

We report preparation of c-axis grain-aligned and densified Ca-based cobalt oxides ([Ca₂CoO_3-δ]_0.62CoO₂ and [Ca₂Co_1.3Cu_0.7O₄]_0.62CoO₂) bulks and their thermoelectric properties. The grain alignment was carried out under a strong magnetic field of 3 tesla because these compounds possess easy axes parallel to the c-axis for magnetization with the order of 10^-4 [-]. The densification was performed by a spark plasma sintering (SPS) process. Each sample obtained by combination of the magnetic alignment and SPS methods showed highly conductive and its resistivity perpendicular to the magnetic field for the alignment (H_a) was almost half of that for a sample processed only by SPS. This strongly suggests that the magnetic grain alignment method is effective for development of thermoelectric properties in the Ca-based cobaltites.