Improvement of thermoelectric properties of Ca3Co4O9 using soft chemistry synthetic methods

Abstract

Two solution synthetic methods, sol-gel and a polymeric route, have been studied in order to obtain Ca 3 Co 4 O 9 misfit compounds with improved thermoelectric properties, compared to the classical solid state reaction. A comparison among the final products obtained by these different methods has been performed using DTA, TGA, FTIR X-ray diffraction, scanning electron microscopy, and thermoelectric characterizations. All the samples obtained by solution synthesis show a very significative reduction on the secondary phases content. As a consequence, an important decrease on the electrical resistivity values is produced, compared to the solid state prepared samples, leading to a relatively important power factor raise.

High thermoelectric performance in Bi2-xPbxBa2Co2Oy promoted by directional growth and annealing

“…Nevertheless, since the discovery in 1997 of good TE properties in Na x CoO 2 [5], many studies have been performed in transition metal oxide (TMO's) based materials. These materials, such as [11,12], are based in cheaper, more abundant and environmentally friendly, and chemically stable at high temperatures under air. All these characteristics have greatly increased the interest in these TMO's-based materials.…”

Effect of Ag additions on the Bi_1.6Pb_0.4Sr₂Co_1.8O_x thermoelectric properties

“…The resistivity values in ceramic materials are influenced by a number of different parameters as content and distribution of secondary phases, porosity, oxygen content, etc. As a consequence, many different synthetic methods have been used in order to synthesize thermoelectric and other layered ceramic materials [11][12][13][14][15][16][17][18]. On the other hand, layered cobaltites are materials with a strong crystallographic anisotropy; therefore the alignment of plate-like grains by mechanical and/or chemical processes has been studied to attain macroscopic properties comparable Bi 1.6 Pb 0.4 Sr 2 Co 1.8 O x thermoelectric ceramics with small Ag additions (0, 1, and 3 wt.%) have been successfully produced by a sol-gel method via nitrates.…”

Processing effects on the thermoelectric properties of Bi₂Ca₂Co_1.7O_x ceramics

“…Since the discovery of this thermoelectric oxide, much work has been performed on the cobaltite ceramics as promising thermoelectric materials for high temperature applications. The intense research work continues on Co-oxide based materials, such as Ca 3 Co 4 O 9 , LaCoO 3 , Bi 2 Sr 2 Co 2 O 9 and Bi 2 Ca 2 Co 2 O y with interesting thermoelectric properties and high working temperatures [6][7][8][9]. Moreover, these oxide materials have the great advantage of being able to operate at high temperatures in air without degradation, in comparison to the intermetallic thermoelectric compounds, which is another way for improving the ZT values.…”