Improvement of thermoelectric properties of Ca0.9Gd0.1MnO3 by powder engineering through K2CO3 additions

Abstract

Oxide materials based on calcium manganite show clear prospects as thermoelectrics, provided by their stability at high temperatures and inherent flexibility in tuning the relevant electrical and thermal transport properties. Donor-doped CaMnO 3 is an n-type semiconductor with a perovskite structure and relatively high thermoelectric performance. In this work, the precursor powders have been modified through potassium carbonate additions to produce Ca 0.9 Gd 0.1-MnO 3 pellets without the usual delamination problems occurring during the compaction process. In order to demonstrate the relevant effects, several samples with different amounts of potassium carbonate (0-15 wt%) have been prepared. The results showed that potassium additions significantly facilitate the compaction procedure, while also improving the thermoelectric performances. The results also highlight the importance of porosity control for improving ZT, by decreasing the thermal conductivity without reduction of the electrical performance. The highest ZT values were observed for the samples processed at 15 wt% of potassium carbonate addition, exhibiting an improvement at least 30% at 800°C when compared to the pure samples.

Tuning thermoelectric properties of Ca0.9Gd0.1MnO3 by laser processing

“…As it can be observed in the graph, all samples present semiconducting behaviour, except for the lowest growth rate samples, in the whole measured temperature range. This behaviour is different from the typical obtained in this family, which is metallic for sintered materials [3,4,10,22]. This difference clearly reflects the fact that as-grown samples possess very high density (Table 1) and, consequently, oxygen diffusion to the inner part of the 60 m 60 m 60 m 60 m samples is hindered during annealing, even at high temperatures (Table 2).…”

“…Transition oxides-based ceramics are one of the most promising, due to their high thermal and chemical stability when working under oxidizing atmospheres, at high temperatures [1]. Among the n-type semiconductor oxides, CaMnO 3 is regarded as one of the most suitable ones [2][3][4][5][6][7][8]; however, this compound possesses limited TE performances due to its low carrier concentration [1 -6]. Consequently, many studies have been carried out to improve its thermoelectric properties using dopants and different preparation techniques [2][3][4][5][6][9][10][11].…”

“…Among the n-type semiconductor oxides, CaMnO 3 is regarded as one of the most suitable ones [2][3][4][5][6][7][8]; however, this compound possesses limited TE performances due to its low carrier concentration [1 -6]. Consequently, many studies have been carried out to improve its thermoelectric properties using dopants and different preparation techniques [2][3][4][5][6][9][10][11]. These studies are essentially focused on the improvement of electrical conductivity, without drastically affecting Seebeck coefficient or thermal conductivity.…”

“…These studies are essentially focused on the improvement of electrical conductivity, without drastically affecting Seebeck coefficient or thermal conductivity. On the other hand, doping processes have already proved to increase electrical conductivity and, simultaneously, reduce thermal conductivity [4,[11][12][13]. This is of the main importance, as the thermoelectric performances are evaluated using the dimensionless figure-ofmerit, ZT, which combines Seebeck coefficient (S), absolute temperature (T), electrical resistivity (), and thermal conductivity (), and it is defined as S 2 T/ [1,14], where S 2 / is called power factor, PF.…”

“…The results of electrical resistivity have been well correlated to the Mn valence and oxygen deficiency. Moreover, they have verified that gadolinium doping on the calcium site reduces the electrical resistivity and thermal conductivity values [4,5].…”