Using thermoforging process, dense Ca3Co4O9 (Co349) thermoelectric oxides have been successfully textured. The various parameters influencing the formation of the Co349-textured material have been investigated. The electrical transport measurements show an anisotropy of the resistivity in good agreement with scanning electron microscopy observations. Texture is quantified by neutron-diffraction measurements and correlated to anisotropic resistivity measurements and Seebeck coefficients.

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Hole-doped Ca 3 Co 4 O 9 (Co349) ceramics were prepared using solid-state reaction. Two processing strategies have been used to produce the thermoelectric oxide ceramics, Conventional and Spark Plasma (SPS) Sintering to control the grains consolidation, texturation and sample densification. Thermoelectric properties were measured and the influence of the processing conditions on the properties was evidenced. SPS favours shorter elaboration times and produces samples with larger thermoelectric properties due to better densification and alignment. The effect of the free deformation and texturation using the SPS technique is discussed. Seebeck coefficient values of 180 μV/K at 873 K are obtained.

Zn-and Ti-doped thermoelectric misfit cobalt oxides Ca 3 Co 4-x-y Zn x Ti y O 9 (x = 0-0.5, y = 0-0.5) were prepared by solid-phase reaction, sequent uniaxial compression molding and sintering at 1173 K for 20 h. Powder X-ray diffraction data suggest that Zn and Ti dopants substitute in the rocksalt layer rather than in the CoO 2 layer for x ≤ 0.1 and y ≤ 0.1, respectively. In Zn and Ti single-doped samples for x ≤ 0.1 and y ≤ 0.1, ZT at room temperature increased with x and y through an increase in the absolute Seebeck coefficients despite the decrease in electrical conductivities. In Zn and Ti double-doped samples, minor phases other than the misfit oxides were observed at approximately x + y ≥ 0.1. At x ≤ 0.1 and y ≤ 0.1 double doping improved the thermoelectric properties. ZT at room temperature reached a maximum value of 0.035 at (x, y) = (0.1, 0.03).

In this work we describe (i) the fabrication of thermoelectric modules based on oxide bulk and foam materials of Ca3Co4O9 and Ca0.95Sm0.05MnO3(ii) and the metal to ceramic contacts preparation. The open porous foam structures of thermoelectric materials can result in designing efficient thermoelectric modules for waste heat sources involving gaseous and liquid media. The possibility of direct large area physical contact of thermoelectric foam elements with hot media will make them efficient electric power generators. The open porous thermoelectric materials with holes can be a good candidate to confine phonons (lattice vibrations) in order to reduce the thermal conductivity if the pores can be made sufficiently small. The performances of the modules were evaluated and possible factors limiting their theoretical performance are discussed. A parameter representing the quality of the modules termed as manufacturing factor (MF) representing the cumulative effect of various factors involved in the fabrication process is introduced and evaluated for the modules and compared to the reported modules.

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