All-oxide thermoelectric module with in situ formed non-rectifying complex p-p-n junction and transverse thermoelectric effect

Abstract

All-oxide thermoelectric modules for energy harvesting are attractive due to high temperature stability, low cost, and the potential to use non-scarce and non-toxic elements. Thermoelectric modules are mostly fabricated in the conventional π-design, associated with the challenge of unstable metallic interconnects at high temperature. Here, we report on a novel approach to fabrication of a thermoelectric module with an in situ formed p-p-n junction made of state-of-the-art oxides Ca3Co4-xO9+δ (p-type) and CaMnO3-CaMn2O4 composite (n-type). The module was fabricated by spark plasma co-sintering of p- and n-type powders partly separated by insulating LaAlO3. Where the n- and p-type materials originally were in contact, a layer of p-type Ca3CoMnO6 was formed in situ. The hence formed p-p-n junction exhibited ohmic behavior and a transverse thermoelectric effect, boosting the open circuit voltage of the module. The performance of the module was characterized at 700 - 900 °C, with the highest power output of 5.7 mW (around 23 mW/cm2) at 900 °C and a temperature difference of 160 K. The thermoelectric properties of the p- and n-type materials were measured in the temperature range 100 - 900 °C, where the highest zT of 0.39 and 0.05 were obtained at 700 and 800 °C, respectively, for Ca3Co4-xO9+δ and the CaMnO3-CaMn2O4 composite.