Thermoelectric Ceramics Based on the Layered Cobaltates of Bismuth and Alkaline-Earth Metals

Abstract

Using solid-state reactions method the ceramic samples of (Bi,Pb) 2 Ba 2 (Co,M) 2 O y , (Bi,Pb) 2 Sr 2 (Co,M) 1.8 O y , and (Bi,Pb) 2 Ca 2 (Co,M) 1.7 O y (M = Mn, Zn) solid solutions had been prepared, their lattice constants had been determined and their thermal expansion, electrical conductivity and thermo-EMF had been measured, and their power factor had been calculated. Effect of the bismuth substitution by lead and cobalt substitution by manganese and zinc in the layered cobaltates of bismuth and alkaline-earth metals (AEM) on the crystal structure and physicochemical and functional properties of their derivatives was analyzed. It was found that cobaltates studied are p-type conductors, which linear thermal expansion coefficient (LTEC) values varied within (9.68-13.2)•10-6 K-1. Power factor values for the samples studied unmonotonously changed when temperature increased and at 1000 K were maximal for Bi 2 Ba 2 Co 2 O y , Bi 2 Sr 2 Co 1.7 Mn 0.1 O y , and Bi 2 Ca 2 Co 1.7 O y compounds − 12.1, 10.1, and 10.6µW/(m⋅K 2) respectively.

Thermoelectric modules built using ceramic legs grown by laser floating zone

“…The values obtained for this n-and p-type fibres are similar to those previously reported in the literature and explained elsewhere [10,11,13,23,33].…”

“…At higher temperatures, the expansion curves show deviations from linearity, which may be attributed to changes in phase composition, the concentration of point defects, or the rearrangement in the sublattices, possibly combined with oxidative decomposition from Mn 4+ to larger Mn 3+ [34], in the manganite fibres. Moreover, the values obtained for these manganites are within the reported in the literature (9-15 × 10 −6 /K) [33,[36][37][38].…”

“…5c. BiBaCoO fibres have reached PF values close to 0.1 mW/K 2 m at 923 K, which are within the reported for these grown materials [10,11,23], but higher than for those prepared via solid-state route [33]. On the other hand, while CLMO fibres present similar PF values to the determined in BBCO fibres, the CMNO ones possess much lower values (0.03 mW/K 2 m at 923 K), due to their microstructural characteristics, such as the existence or not of trends in the grain orientation to the growth axis [13].…”

“…The maximum values at 923 K observed for the manganite samples (~10-100 S/cm) are in the same order of those obtained for similar CaMnO 3 -based materials [30][31][32]. BBCO samples also present similar conductivities to the ones reported in the literature (~100 S/cm) for laser processed samples [10,23], and higher than for samples prepared by solid-state route (~10-80 S/cm) [33][34][35].…”

“…The obtained mean thermal expansion coefficient for the BBCO fibres (12.6-13.4 × 10 −6 /K) are slightly higher than the reported for solid-state prepared samples (9.68-13.2 ×10 −6 /K) [33]. On the other hand, they are in the range of values reported in similar materials, which point out to the influence of composition and processing method on the mean thermal expansion coefficient values [33,39].…”