Abstract
CaMnO3–based materials represent a promising family of n-type oxide thermoelectrics. The objective of the present work is assessing the impacts on relevant structural, microstructural and thermoelectric properties of manganites when they are processed by the laser floating zone technique. For this purpose, donor-doped Ca0.9La0.1MnO3, CaMn0.95Nb0.05O3 and undoped CaMnO3 were used. Different growth conditions have been evaluated through combined studies of structural, microstructural, and thermoelectric characteristics. Despite the presence of secondary phases, electrical resistivity is among the best reported in the literature (9 mΩ.cm at 800 °C for La-doped materials grown at 200 mm/h). Essentially high absolute Seebeck coefficient of 320 μV/K at 800 °C was observed for undoped samples grown at 10 mm/h. Power factor is significantly affected by the growth conditions, reaching the highest values when using the lowest pulling rates. Exceptionally high PF (0.39 mW/K2m at 800 °C) was obtained for undoped CaMnO3 samples grown at 10 mm/h.
Highlights
Thermoelectric (TE) energy conversion has been shown as an effective technology that can be used to transform directly thermal to electrical energy without moving parts or other dissipative systems
In this figure it can be clearly seen that room temperature resistivity is decreased when the growth rates are reduced which confirms the higher grain size and orientation found in samples grown at lower rates
When comparing the S values at room temperature, it can be observed that they follow a parallel evolution with the electrical resistivity, they decrease with the growth rates
Summary
Thermoelectric (TE) energy conversion has been shown as an effective technology that can be used to transform directly thermal to electrical energy without moving parts or other dissipative systems. TE power generation technology is regarded as one of the most promising methods to harvest energy from different natural and/or wasted heat sources These materials can be applied in classical energy transformation systems improving their efficiency. TE materials with high-energy conversion efficiency are strongly required for electric power generation before they can be considered for practical applications The performances of these type of materials are quantified by the dimensionless figure of merit, ZT, which is defined as TS2/ρκ (where S is the Seebeck coefficient, T the absolute temperature, ρ the electrical resistivity and κ the thermal conductivity). The aim of the present study is studying the effect of growth rate on the microstructure and TE properties of Bi2Ba2Co2Ox textured ceramics fabricated by the LFZ technique
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