Eu-Substituents-Induced Modifications in the Thermoelectric Properties of the Zintl Phase Ba<sub>1-<i>x</i></sub>Eu<i><sub>x</sub></i>Zn<sub>2</sub>Sb<sub>2</sub> System
Four quaternary Zintl phase thermoelectric (TE) materials belonging to the Ba<sub>1-<i>x</i></sub>Eu<i><sub>x</sub></i>Zn<sub>2</sub>Sb<sub>2</sub> (<i>x</i> = 0.02(1), 0.04(1), 0.08(1), 0.15(1)) system were successf...
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| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
MDPI AG
2025-01-01
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| Series: | Molecules |
| Subjects: | |
| Online Access: | https://www.mdpi.com/1420-3049/30/2/310 |
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| Summary: | Four quaternary Zintl phase thermoelectric (TE) materials belonging to the Ba<sub>1-<i>x</i></sub>Eu<i><sub>x</sub></i>Zn<sub>2</sub>Sb<sub>2</sub> (<i>x</i> = 0.02(1), 0.04(1), 0.08(1), 0.15(1)) system were successfully synthesized using the molten Pb-flux or the conventional high-temperature reaction methods. Their crystal structures were characterized by both powder and single-crystal X-ray diffraction analyses, and all four isotypic title compounds adopted the orthorhombic BaCu<sub>2</sub>S<sub>2</sub>-type (<i>Pnma</i>, <i>Z</i> = 4, Pearson code <i>oP</i>20) structure. The radius ratio criterion, based on the cationic and anionic elements (i.e., <i>r</i><sub>+</sub>/<i>r</i><sub>−</sub>), was successfully verified in the title system, as in our previous reports, where <i>r</i><sub>+</sub>/<i>r</i><sub>−</sub> > 1 for the BaCu<sub>2</sub>S<sub>2</sub>-type structure. A series of density functional theory calculations were performed using a hypothetical model with the idealized compositions of Ba<sub>0.75</sub>Eu<sub>0.25</sub>Zn<sub>2</sub>Sb<sub>2</sub>, and the results were compared with the ternary parental compound BaZn<sub>2</sub>Sb<sub>2</sub> to understand the influence of Eu substituents in the Ba<sub>1-<i>x</i></sub>Eu<i><sub>x</sub></i>Zn<sub>2</sub>Sb<sub>2</sub> system. A similar overall shape of the density of states (DOS) curves and the near-constant DOS values at <i>E</i><sub>F</sub> before and after the cationic substitution suggest only marginal changes in the carrier concentration. Therefore, carrier mobility has a dominant role in rationalizing the observed variations in the electrical transport properties of the title system. Temperature-dependent TE property measurements proved that an increase in the Seebeck coefficient <i>S</i> and a decrease in electrical conductivity <i>σ</i> were observed as the Eu substituents gradually increased in the Ba<sub>1-<i>x</i></sub>Eu<i><sub>x</sub></i>Zn<sub>2</sub>Sb<sub>2</sub> system, although the overall <i>S</i> and <i>σ</i> values were lower than those in the parental compound BaZn<sub>2</sub>Sb<sub>2</sub>. The thermal conductivities of these title compounds were successfully lowered by phonon scattering, but due to the overall smaller electrical transport properties, the observed maximum <i>ZT</i> was 0.49 at 773 K for Ba<sub>0.98(1)</sub>Eu<sub>0.02</sub>Zn<sub>2</sub>Sb<sub>2</sub>. |
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| ISSN: | 1420-3049 |