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

S. Horii¹, I.Matsubara², K. Fujie¹, W. Shin², N. Murayama²,J. Shimoyama^1,3, K. Kishio¹

¹Department ofSuperconductivity, University of Tokyo, Hongo 7-3-1, Tokyo 113-8656, Japan

²National Institute ofAdvanced Industrial Science and Technology, Nagoya 463-8560, Japan

³PRESTO,Japan Science and Technology Corporation, Saitama 332-0012, Japan

We report preparation ofc-axis grain-aligned and densified Ca-based cobalt oxides ([Ca₂CoO_3-d]_0.62CoO₂ and [Ca₂Co_1.3Cu_0.7O₄]_0.62CoO₂)bulks and their thermoelectric properties. The grain alignment was carried outusing a strong magnetic field because these compounds possess easy axesparallel to the c-axisfor magnetization. The densification was performed by two different processes,intermediate uniaxial pressing (IP) and spark plasma sintering (SPS).Consequently, each sample obtained by combination of the magnetic alignment andSPS methods showed highly conductive and its resistivity perpendicular to analignment field was almost half of that for a sample processed only by SPS.This strongly suggests that the magnetic grain alignment method is effectivefor development of thermoelectric properties in the Ca-based cobaltites.