Fabrication of textured thermoelectric layered cobaltites with various rock salt-type layers by using β-Co(OH)2platelets as reactive templates

Abstract

Textured bulk ceramics have been prepared of various cobaltites including the common CdI2-type CoO2 layer (i.e., [Ca2(Co0.65Cu0.35)2O4]0.624[CoO2]: CCO-4-layer, [Bi2M2−xO4]p[CoO2] (M2 = Sr2: BSCO, M2 = Ca1Sr1: B(SC)CO, M2 = Ca2: BCCO)) by using β-Co(OH)2 (CdI2-type) platelets as reactive templates, and their thermoelectric (TE) properties have been examined. All the specimens were found to be highly c-axis aligned ceramics. Especially for CCO-4-layer, B(SC)CO and BCCO, the present study is the first report on the fabrication of textured ceramics. Our textured ceramic specimens exhibited larger values of electrical conductivity (σ) than the ceramics prepared by a conventional solid-state reaction (SSR specimens): e.g., σab = 0.46 × 104 S m−1 for the textured specimen and σSSR = ∼0.26 × 104 S m−1 at 1060 K for the SSR specimen for BCCO. This study indicated that our preparation method using β-Co(OH)2 templates is a versatile and effective technique to fabricate cobaltites, including CoO2 layers, with a high degree of orientation and improved TE properties.