Abstract
[Bi2Ba2O4]p[CoO2] thermoelectric ceramics have been successfully grown from the melt using the laser floating zone method, followed by a thermal treatment at 700 °C under air between 0 and 1532 h. The microstructural, thermoelectric, and mechanical properties were evaluated as a function of the thermal treatment length. Microstructure has shown that as-grown samples are composed of thermoelectric grains, together with a relatively high amount of secondary phases. Thermal treatment decreased the number and amount of secondary phases, producing nearly single-phase samples after 384 h. Consequently, the thermoelectric properties evaluated through the power factor showed a slight increase with the thermal treatment length, mainly due to the decrease of electrical resistivity, while the Seebeck coefficient was nearly unchanged. On the other hand, flexural strength was practically constant after 24 h thermal treatment.
Highlights
Nowadays, energy transforming systems possess low efficiency, and more than 50% of their fuel consumption is released as wasted heat [1]
It is clear that in order to reach high ZT values, we need materials with a high S and low ρ and κ, able to work at high temperatures
The electrical part of this expression (S2 /ρ) is called power factor, PF, and it has been shown that its optimization is essential in order to achieve high power density thermoelectric modules [4]
Summary
Energy transforming systems possess low efficiency, and more than 50% of their fuel consumption is released as wasted heat [1]. Thermoelectric (TE) materials can transform thermal to electrical energy without any moving parts, being able to harvest waste heat from a wide number of systems, increasing their efficiency, and decreasing the CO2 emissions They can play a very important role in combating global warming. These materials can be oxidized and/or degraded at high temperatures under air and/or release toxic or heavy elements Their application range is limited to relatively low temperatures. Both sublattices (RS block and CdI2 -type CoO2 layer) possess common a- and c-axis lattice parameters and β angles, but different b-axis length, causing a misfit along the b-direction [17] These materials show a very important crystallographic anisotropy which influences their electrical properties. The microstructural, thermoelectric, and mechanical evolution of textured [Bi2 Ba2 O4 ]p [CoO2 ] samples produced through the laser floating zone technique have been studied as a function of the thermal treatment length at 700 ◦ C under air (between 0 and 1532 h)
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