Authors: DongWei MA | Jing Zhang | Huijuan Geng | Di Yuan | Gui Lin Yang
Source: Zhongguo kexue. Wulixue Lixue Tianwenxue (article, 2020-03-18)
Field: Materials Science — Materials Chemistry

The structural, electronic, elastic and high thermoelectric properties of a new Zintl compound Ba&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;Sn&amp;lt;sub&amp;gt;3&amp;lt;/sub&amp;gt;Sb&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt; studiedby first principles <p indent="0mm">The structural, electronic, elastic, and thermoelectric properties of a new recently synthetized Zintl compound Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> are studied using the first principles and the Boltzmann theory. We determine the requirements of the chemical potentials for the formation of Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub>. On the basis of the mechanical stability criteria and the phonon spectrum of Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub>, the lattice structure is determined to be thermodynamically stable. The electron density difference of Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> shows that there is an ionic bond between Ba and the [Sn<sub>3</sub>Sb<sub>4</sub>] cluster, and a covalent Sn–Sb bond in [Sn<sub>3</sub>Sb<sub>4</sub>]. The coexistence of ionic and covalent bonds indicates that Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> is a typical Zintl compound. The calculated electronic band structure shows that Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4 </sub>is an indirect semiconductor with a band gap <sc>~0.29 eV.</sc> In the conduction bands, the presence of multivalley bands benefits the thermoelectric properties. In terms of the Slack model, the lattice thermal conductivity <italic>κ</italic><sub>l</sub> is smaller than <sc>0.5 W m<sup>−1</sup> K<sup>−1</sup></sc> when the temperature is over <sc>720 K.</sc> On the basis of the analysis of the band structure, we calculate the thermoelectric properties using the Boltzmann theory. The results show that p-type-doped Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> undergoes interesting changes. Because pristine Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> is an n-type semiconductor, the Seebeck coefficient of p-type-doped Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> changes from negative to positive at <italic>T</italic><sc>=500 K</sc> or <italic>T</italic><sc>=700 K.</sc> For p-type-doped Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub>, the calculated largest <italic>ZT</italic> is 0.09. For n-type-doped Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub>, the Seebeck coefficient exhibits bipolar effects at <italic>T</italic><sc>&gt;500 K.</sc> This result is obtained because thermal excitation becomes strong with an increase in the temperature, and the effect of the minor carriers leads to the change of the <italic>S</italic> value. The optimized largest <italic>ZT</italic> value of n-type-doped Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4</sub> is up to 0.26 with <italic>n</italic>=1.14×10<sup>20</sup> cm<sup>−3</sup> at <italic>T</italic><sc>=700 K,</sc> which is almost three times that of p-type-doped Ba<sub>3</sub>Sn<sub>3</sub>Sb<sub>4.</sub> Ampere ; Thermoelectric effect ; Materials science ; Chemistry ; Electrical engineering ; Physics ; Engineering ; Current (fluid) ; Thermodynamics Advanced Thermoelectric Materials and Devices ; Thermal properties of materials ; Thermodynamic and Structural Properties of Metals and Alloys