Exploring the high-temperature thermoelectric performance of la-substituted Ca3Co4O9 bulk ceramics

It is well-known that the electrical properties of the Ca3Co4O9 thermoelectric (TE) compound are strongly influenced by the valence of the substituting cation, while its solubility and “functional” impact depend largely on the preparation and/or processing methods used. Furthermore, this material’s hybrid crystal structure allows for different cation substitutions in/from different sublattices. This research work presents the relevant effects of different La substitutions for the Ca ions from the insulating rock salt type [Ca2CoO3] crystal component (considered as a “charge reservoir” for the conductive [CoO2] layers) for a series of bulk samples prepared and processed via a solid-state method, chosen for simplicity. The results show that the actual level of La substitutions does not exceed 0.03 (x < 0.03), in Ca3-xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07, and that beyond this limit, simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La,Ca)CoO3 phase formation take place. The morpho-structural features were found to be quite moderate, with a negligible effect on the charge carries transport. The electrical measurements and average oxidation state of cobalt (~3.11) suggest that the substitutions with La have only a minor effect on the charge carrier concentration. The electrical resistivity of the samples with x = 0.01, 0.03 and 0.05 is found to be ~1.3 times lower than of pristine Ca3Co4O9, while the changes in the Seebeck coefficient values are only moderate in the whole measured temperature range. The highest power factor, representing the electrical counterpart of the TE performance, was found for the Ca2.99La0.01Co4O9 samples (~0.28 mW/K2m, at 800 C), being among the best found in the literature for similar materials. Our results suggest that low substitutions with rare-earth cations in the “charge reservoir” layers of the Ca3Co4O9 compound can be promising in designing and improving these p-type oxides, provided by the strongly correlated nature of their conduction mechanism.publishe

Growth rate effects on the thermoelectric performance of CaMnO3-based ceramics

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/hpublishe

Significant enhancement of the thermoelectric performance in Ca3Co4O9 thermoelectric materials through combined strontium substitution and hot-pressing process

This work explores the possibilities for a further enhancement of the thermoelectric properties of Ca3Co4O9 by Sr-doping combined with hot-pressing. Modified hot-pressing process resulted in highly-textured and dense ceramics. Sr-doping significantly improves electrical properties, resulting in extremely large power factor (1.2 mW/K2m at 800 °C) due to simultaneous electrical resistivity decrease and Seebeck coefficient increase. The main effect on cumulative electrical performance is provided by the Seebeck coefficient, reaching 270μV/K at 800 °C. XPS revealed relatively high average cobalt oxidation state at room temperature (+3.3), compared to materials produced by conventional sintering. The results of combined XPS and Auger electron spectroscopy emphasize the importance of high densification in Ca3Co4O9-based ceramics for preventing phase decomposition and interaction with CO2 and moisture. Still, despite the exceptional electrical performance, the calculated figure-of-merit (estimated as 0.29 at 800 °C) is around the best reported in the literature due to a high thermal conductivity (4.4 W/K m at room temperature).publishe

СРАВНИТЕЛЬНЫЙ АНАЛИЗ ВОССТАНОВЛЕНИЯ CYP124 M. TUBERCULOSIS РАЗЛИЧНЫМИ РЕДОКС-ПАРТНЕРАМИ

In order to determine the optimal redox partners of CYP124 M. tuberculosis in reconstituted in vitro system we carried out heterologous expression, isolation and purification of recombinant CYP124 Mycobacterium tuberculosis and candidate redox partners: Fdx, FdR, FprA, Adx, AdR, CPR, Arh1_A18G, Etpfd. CYP124 was shown to exhibit the highest catalytic activity in system with S. pombe mitochondrial electron transfer proteins: Etp1fd и Arh1_A18G.С целью определения оптимальных редокс-партнеров CYP124 M. tuberculosis в in vitro реконструированной системе осуществлена гетерологическая экспрессия, выделение и очистка рекомбинантных цитохрома CYP124 M. tuberculosis и потенциальных редокс-партнеров: Fdx, FdR, FprA, Adx, AdR, CPR, Arh1_A18G, Etpfd. Показано, что CYP124 проявляет наибольшую каталитическую активность в системе с митохондриальными электрон-транспортными белками S. pombe: Etp1fd и Arh1_A18G