Effect of synthesis process on the densification, microstructure, and electrical properties of Ca_0.9Yb_0.1MnO₃ ceramics

Abstract

Ca0.9Yb0.1MnO3 thermoelectric materials have been prepared, through a classical solid‐state sintering method, from attrition‐ and ball‐milled precursors. After calcination step, microstructural observations have shown that attrition‐milled precursors possess much smaller particle sizes than the obtained by ball milling. Smaller precursors sizes lead to higher reactivity, producing higher density, hardness, and thermoelectric phase content in the sintered materials. The thermoelectric properties reflect the microstructural features, decreasing electrical resistivity in the attrition milling prepared samples without a drastic decrease in the Seebeck coefficient. As a consequence, power factor values are higher than the obtained in the classical solid‐state method samples. Moreover, the highest power factor values at 800°C are much higher than the best results obtained in this CaMnO3 family. As a result, it has been found that it is possible to tailor the thermoelectric properties of Ca0.9Yb0.1MnO3 ceramics by designing the appropriate preparation procedure while keeping in mind its industrial scalability.

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

“…9, the electrical resistivity evolution of samples with temperature, as a function of K 2 CO 3 content is presented. All samples present metallic behaviour in the whole measured temperature range, in accordance with the literature data [3,6,8,21]. The results suggest that K 2 CO 3 addition drastically decreases electrical resistivity values.…”

“…The S values are negative at all temperatures, showing that dominant carriers are electrons in all samples. Furthermore, absolute values are increasing with the temperature, which is the typical behaviour in the manganites family [6,21,27,28]. In addition, all samples display very similar values at the measured temperatures, indicating that Mn likely possesses the same oxidation states in all of them, independently of K 2 CO 3 addition.…”

“…It is known that preparation routes present a significant impact on the thermoelectric performance. Microstructural tuning is quite effective for decreasing the electrical resistivity and thermal conductivity, while increasing, or maintaining practically constant, Seebeck coefficient [6]. Consequently, in ceramic materials good and clean grain connections should be obtained to avoid adverse effects on the carrier mobility, improving the electrical conductivity without drastically modifying the thermal conductivity.…”

Effect of simultaneous K, and Yb substitution for Ca on the microstructural and thermoelectric characteristics of CaMnO3 ceramics

“…1. At a first sight it is clear that the highest peaks (identified by their diffraction planes) correspond to the thermoelectric phase [8,14]. Moreover, the CaMn 2 O 4 phase can be also identified through the small intensity peaks (shown by *) [15].…”

“…These advantages impelled the research in this field, finding new materials with both pand n-type conduction. Among all these materials, it is possible to highlight the CoO-and MnO-based ones, respectively [5][6][7][8]. On the other hand, the main problem associated to these TE ceramics is their relative low performance, even at high temperatures.…”