Thermoelectric Properties of Ca<sub>3</sub>Co<sub>2−<i>x</i></sub>Mn<i><sub>x</sub></i>O<sub>6</sub> (<i>x</i> = 0.05, 0.2, 0.5, 0.75, and 1)

oleh: Nikola Kanas, Sathya Prakash Singh, Magnus Rotan, Temesgen Debelo Desissa, Tor Grande, Kjell Wiik, Truls Norby, Mari-Ann Einarsrud

Format: Article
Diterbitkan: MDPI AG 2019-02-01

Deskripsi

High-temperature instability of the Ca<sub>3</sub>Co<sub>4&#8722;<i>y</i></sub>O<sub>9+<i>&#948;</i></sub> and CaMnO<sub>3&#8722;<i>&#948;</i></sub> direct p-n junction causing the formation of Ca<sub>3</sub>Co<sub>2&#8722;<i>x</i></sub>Mn<i><sub>x</sub></i>O<sub>6</sub> has motivated the investigation of the thermoelectric performance of this intermediate phase. Here, the thermoelectric properties comprising Seebeck coefficient, electrical conductivity, and thermal conductivity of Ca<sub>3</sub>Co<sub>2&#8722;<i>x</i></sub>Mn<i><sub>x</sub></i>O<sub>6</sub> with <i>x</i> = 0.05, 0.2, 0.5, 0.75, and 1 are reported. Powders of the materials were synthesized by the solid-state method, followed by conventional sintering. The material Ca<sub>3</sub>CoMnO<sub>6</sub> (<i>x</i> = 1) demonstrated a large positive Seebeck coefficient of 668 &#956;V/K at 900 &#176;C, but very low electrical conductivity. Materials with compositions with <i>x</i> &lt; 1 had lower Seebeck coefficients and higher electrical conductivity, consistent with small polaron hopping with an activation energy for mobility of 44 &#177; 6 kJ/mol and where both the concentration and mobility of hole charge carriers were proportional to 1&#8722;<i>x</i>. The conductivity reached about 11 S&#183;cm<sup>&#8722;1</sup> at 900 &#176;C for <i>x</i> = 0.05. The material Ca<sub>3</sub>Co<sub>1.8</sub>Mn<sub>0.2</sub>O<sub>6</sub> (<i>x</i> = 0.2) yielded a maximum <i>zT</i> of 0.021 at 900 &#176;C. While this value in itself is not high, the thermodynamic stability and self-assembly of Ca<sub>3</sub>Co<sub>2&#8722;<i>x</i></sub>Mn<i><sub>x</sub></i>O<sub>6</sub> layers between Ca<sub>3</sub>Co<sub>4&#8722;<i>y</i></sub>O<sub>9+<i>&#948;</i></sub> and CaMnO<sub>3&#8722;<i>&#948;</i></sub> open for new geometries and designs of oxide-based thermoelectric generators.