Enhancement of the thermoelectric properties of directionally grown Bi–Ca–Co–O through Pb for Bi substitution

Abstract

Thermoelectric performances on cobaltite ceramics can be changed by doping followed by grain orientation methods. This can be performed by the Laser Floating Zone (LFZ) method on samples with different substitutions in the Rock Salt sublattice. In this work, Bi 2−x Pb x Ca 2 Co 1.7 O y (x = 0.0, 0.2, 0.4 and 0.6) ceramics have been directionally grown at 30 mm/h. In all the cases, samples show a microstructure composed, mainly, of alternated grains of the thermoelectrical phase and the solid solution Bi(Pb)-Ca-O, with small CoO inclusions. It has been found an important improvement on the resistivity and thermopower for samples with 0.4 Pb substitution, leading to power factor values higher than usual in misfit cobaltites obtained by conventional solid state routes.

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

“…Other possibilities arising from the crystallographic structure of these materials are the cationic substitutions in the RS layer, which can change the misfit relationship between the two layers and, as a consequence, modifying the values of the thermopower [7]. From this point of view, it is clear that this kind of substitutions can be useful in order to improve thermoelectric performances of ceramic materials [19], as it is reported for the substitution of Gd and Y for Ca [23], or Pb for Bi [24][25][26]. Moreover, metallic Ag additions have also shown to improve, in an important manner, the mechanical and electric properties of this system [27] and other similar materials [28] which nearly do not react with Ag, as it has been found in some phase diagram studies [29].…”

Growth rate effect on microstructure and thermoelectric properties of melt grown Bi2Ba2Co2Oxtextured ceramics

“…As a consequence, the samples grown by this technique show a reduction of electrical resistivity, but usually lower than expected due to the simultaneous secondary phases formation. 15 On the other hand, previous studies on laser grown samples have shown that the textured samples produced by this technique possess, at the same time, higher Seebeck coefficient values than usual in these systems due to the raise on the oxygen vacancies. 16 In this context, the aim of the present study is studying the effect of growth rate on the microstructure and TE properties of Bi 2 Ba 2 Co 2 O x textured ceramics fabricated by the LFZ technique.…”

Tailoring Ca3Co4O9 microstructure and performances using a transient liquid phase sintering additive

“…As bulk materials, these oxides usually demonstrate quite low thermoelectric performance, which make them no feasible for any practical applications. Envisaging the increment of ZT, many processing and structural engineering routes were attempted, including cationic substitution in solid state sintered materials [4,5], or taking advantage of their crystallographic nature to align the grains into a preferential direction using well-known techniques such as templated grain growth (TGG) [6], hot-pressing [7], spark plasma sintering (SPS) [8], laser floating zone (LFZ) [9], or the recently developed electrically assisted laser floating zone (EALFZ) [10]. These texturing techniques have been reported to produce bulk high density materials with well oriented grains, leading to enhanced electrical conductivity.…”