Synthesis of textured thermoelectric layered cobaltites by reactive templated grain growth

Abstract

In order to apply layered cobaltites to thermoelectric (TE) devices, we need aligned ceramics to exploit their superior in-plane TE properties. Here, we report the preparation and characterization of c-axis aligned [Ca/sub 2/CoO/sub 3/]/sub 0.62/[CoO/sub 2/] (CCO) ceramics by the reactive templated grain growth (RTGG) method. As reactive templates, we synthesized platelike /spl beta/-Co(OH)/sub 2/ particles by a precipitation method. The template particles were mixed with a complementary reactant, CaCO/sub 3/, and aligned by a tape-casting. Upon heat treatment, they reacted to form a CCO ceramic with almost perfectly c-alignment (Lotgering's orientation degree, f > 0.99). The highly textured ceramic shows significantly large in-plane electrical conductivity (/spl sigma//sub ab/): i.e., the value of /spl sigma//sub ab/ was 2.61 /spl times/ 10/sup 4/ S/m at 1060 K, where the value is around 60 % of that of a single crystal. We conclude that the RTGG method must be an effective and versatile technique for the preparation of large-sized TE materials with high TE performances.