Fabrication of texturedthermoelectric layered cobaltites with various rocksalt-type subsystems

H.Itahara, C. Xia, J. Sugiyama, T. Tani

Toyota Central Researchand Development Labs. Inc., 41-1, Nagakute, Aichi 480-1192, Japan

Various layeredcobaltites are reported to exhibit ‘good’ thermoelectric properties.In order to use them for thermoelectric devices, we need aligned polycrystals(or single crystals) due to large anisotropy of the cobaltites. Here, we reportthe preparation and characterization of the aligned [Ca₃CoO₂]_0.62CoO₂(3L-CCO), [Ca₂(Co_0.65Cu_0.35)₂O₄]_0.624CoO₂(4L-CuCCO) and [Bi₂M₂O₄]_pCoO₂(4L-BMCO, M = Sr or Ca) polycrystals. At first, we synthesized Co(OH)₂platelets with ~ 0.5 mm in diameter and ~ 5 in aspectratio by a precipitation technique, then they were used as reactive templatesfor the 3L-CCO, 4L-CuCCO and 4L-BMCO. That is, the aligned Co(OH)₂platelets were reacted with CaCO₃, SrCO₃, Bi₂O₃and/or CuO at 1123 – 1193 K. The obtained polycrystals were almostperfectly aligned along the c axis and showed clear anisotropic properties. The reactive templatedgrain growth (RTGG) technique employed here was confirmed to be a keytechnology for the preparation of large-sized thermoelectric cobaltites withhigh thermoelectric performance.