Phase equilibria in Ca–Co–O system

J Mater Sci: Mater Electron

Constantinescu

Bosque

et al. 2014

Ca 3 Co 4-x Zn x O y (x = 0.01, 0.03, and 0.05) polycrystalline thermoelectric ceramics have been prepared by the classical solid state method. XRD data have shown that Ca 3 Co 4 O 9 is the major phase, with small amounts of the Ca 3 Co 2 O 6 one. Moreover, it has been found that the Zn has been incorporated into these two phases. Slight Zn doping decreases electrical resistivity compared with the values obtained in undoped samples. The minimum values have been obtained for the 0.01-Ni doped samples, increasing for further Zn substitution. Seebeck coefficient does not appreciably change in all the measured temperature range, independently of Zn content. The improvement in electrical resistivity leads to higher power factor values for the 0.01 Zn-doped samples (about 30 %) than for the undoped ones. The maximum power factor at 800°C, around 0.27 mW/K 2 m is significantly higher than the best results obtained in Zn doped samples reported in the literature.

Section: Resultssupporting

confidence: 90%

Doping effect in Ca3Co4−xZnxOy ceramics

J Mater Sci: Mater Electron

Constantinescu

Bosque

et al. 2014

“…In this figure, it has also been indicated the peak at around 38.2 degrees (#) which corresponds to the (111) diffraction plane of Ag [43]. The presence of only Ca 3 Co 4 O 9 phase and Ag in the final samples is a good indication that the twosteps sintering process has been successful, taking into account that the first temperature (1200 ºC) is higher than the Ca 3 Co 4 O 9 phase maximum stability temperature (around 925 ºC) [39], producing the Ca 3 Co 4 O 9 decomposition into CaO(CoO) and CoO(CaO) solid solutions [40]. Moreover, it is also higher than the Ag melting temperature (960 ºC) [41] which could produce liquid Ag losses.…”

Section: Resultsmentioning

confidence: 83%

Enhancement of mechanical and thermoelectric properties of Ca3Co4O9 by Ag addition

Kahraman

Madre

Journal of the European Ceramic Society

et al. 2015

“…The obtained results showed that all samples possess very similar densities, ranging from about 74 % of the theoretical one for the undoped samples to *76 % for the Tidoped ones. These relatively low densities can be easily explained due to the fact that the sintering temperature used in this work (910°C) is far from the melting temperature of this system (*1,350°C), leading to very slow densification kinetics [32]. On the other hand, the sintering temperature is very close to the maximum stability one for the Ca 3 Co 4 O 9 phase (about 925°C) [32].…”

Section: Resultsmentioning

confidence: 86%

Decrease of electrical resistivity in Ca3Co4O9 thermoelectric ceramics by Ti doping

Torres

J Mater Sci: Mater Electron

Bosque

et al. 2014

Ca 3 Co 4-x Ti x O 9 polycrystalline thermoelectric ceramics with small amounts of Ti have been prepared by the classical solid state method. X-ray diffraction data have shown that Ca 3 Co 4 O 9 is the major phase, with small amounts of the Ca 3 Co 2 O 6 one. Moreover, they show that Ti has been incorporated into these two phases. Electrical resistivity decreases, compared with the values for undoped samples, until 0.03-Ti doped ones. Further Ti addition produces an increase of resistivity with respect to the 0.03 Ti doped samples. Seebeck coefficient does not appreciably change in all the measured temperature range, independently of Ti content. The improvement in electrical resistivity leads to about 55 % higher power factor values for the 0.03 Ti-doped samples than that obtained in the undoped ones. The maximum power factor at 800°C, around 0.33 mW/K 2 m, is slightly higher than the obtained in higher density samples, clearly indicating the good thermoelectric performances of these doped samples.