Transport properties in (Na,Ca)Co/sub 2/O/sub 4/ ceramics

Abstract

The resistivity and thermopower of polycrystalline Na 1.1−x Ca x Co 2 O 4 were measured and analyzed. Both the quantities increase with x, suggesting that the carrier density is decreased by the substitutions of Ca 2+ for Na + . Considering that the temperature dependence of the resistivity show a characteristic change with x, the conduction mechanism is unlikely to come from a simple electronphonon scattering. As a reference for NaCo 2 O 4 , single crystals of a two-dimensional Co oxide Bi 2−x Pb x M 3 Co 2 O 9 (M =Sr and Ba) were studied. The Pb substitution decreases the resistivity, leaving the thermopower nearly intact.

Magnetoresistance and magnetothermopower properties of Bi/Ca/Co/O and Bi(Pb)/Ca/Co/O misfit layer cobaltites

“…Because of their composite structure and their large thermopower values, the misfit bismuth based cobaltites have been recently the focus of attention [1][2][3]. These materials have an unusual combination of properties: despite their metallic character with relatively low resistivity, they have rather large Seebeck coefficient ∼+100 µV K −1 , which makes them very promising materials for practical applications.…”

Impurity-induced transition and impurity-enhanced thermopower in the thermoelectric oxideNaCo2−xCuxTerasaki1, Tsukada2, Iguchi3 2002Phys. Rev. BSelf Cite903550View full textAdd to dashboardCite

“…Following NaCo 2 O 4 , other layered cobalt oxides, CaCo-O [5,6,7,8], Bi-Sr-Co-O [9,10,11], Tl-Sr-Co-O [12] have been found to show good thermoelectric performance. In particular, Funahashi et al [8] showed ZT > 1 at 1000 K for Ca-Co-O.…”

Fabrication and thermoelectric characteristics of [(Bi,Pb)2Ba2O4±w]0.5CoO2 bulks with highly aligned grain structure

“…1 In recent years, "misfit-layered cobalt oxides" have been highlighted as next-generational TE materials. [2][3][4][5][6] The members of this material family possess a crystal structure consisting of alternate stacks of a hexagonal CoO 2 layer ͑of the CdI 2 structure͒ and a multi-square-plane layer, M m A 2 O 2+mϮ ͓of the rock-salt ͑RS͒ structure͔. The general chemical formula may be given by ͓M m A 2 O 2+mϮ ͔ q CoO 2 ͑M = Bi, Pb, Co, etc., A = Ba, Sr, etc., m =0, 1, or 2͒, where q is the ratio of b-axis lengths of the two layers, i.e., q ϵ b CoO 2 / b RS .…”