Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide
Active metals such as calcium (Ca)-doped zinc oxide (ZnO)-based thermoelectric (TE) materials are less studied in the literature, primarily due to the expected inherent instability caused by surface hydration. In this work, we synthesized Ca-doped ZnO-based composites (Zn(1−x)CaxO) by doping ZnO wit...
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American Association for the Advancement of Science (AAAS)
2025-01-01
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| Series: | Energy Material Advances |
| Online Access: | https://spj.science.org/doi/10.34133/energymatadv.0140 |
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| author | Xiaosong Tang Sheau Wei Chien Qiang Zhu Zhengyao Qu Jianwei Xu Xizu Wang |
| author_facet | Xiaosong Tang Sheau Wei Chien Qiang Zhu Zhengyao Qu Jianwei Xu Xizu Wang |
| author_sort | Xiaosong Tang |
| collection | DOAJ |
| description | Active metals such as calcium (Ca)-doped zinc oxide (ZnO)-based thermoelectric (TE) materials are less studied in the literature, primarily due to the expected inherent instability caused by surface hydration. In this work, we synthesized Ca-doped ZnO-based composites (Zn(1−x)CaxO) by doping ZnO with CaO nanoparticles using the spark plasma sintering method (0.05 to 0.2 mol. %) and subsequently investigated the TE properties of these Zn(1−x)CaxO composites. Unlike well-known Al- or Ga-doped ZnO composites, Zn(1−x)CaxO exhibited a different behavior from Al- or Ga-doped ZnO. The electrical conductivity of Zn(1−x)CaxO was much improved from being nonconductive to being conductive, achieving an electrical conductivity of 650 S cm−1 when doping with 0.1 mol. % CaO. This improvement is due to the surface hydration of hygroscopic CaO, which forms conductive Ca(OH)2, enhancing the electrical conductivity. However, the electrical conductivity was remarkably decreased after Zn(1−x)CaxO was subjected to annealing at 860 K. In contrast, the Seebeck coefficient, ranging from −90 to −160 μV K−1, was not substantially affected by the high-temperature annealing process, indicating that part of Zn2+ ions were substituted with Ca2+ ions during annealing. Zn(1−x)CaxO composites were studied by x-ray diffraction and x-ray photoelectron spectroscopy. It was found that Zn(1−x)CaxO exhibited a crystal structure similar to that of ZnO. X-ray photoelectron spectroscopy results showed that there are 2 different types of Ca2+ ions in the Zn(1−x)CaxO composites. One type is assigned to Ca2+ ions that substituted for Zn2+ ions in the ZnO lattice, while the other type is Ca2+ ions from nonelectrically conductive free CaO. The temperature-dependent thermal conductivity of ZnO0.99CaO0.01 before and after annealing was examined, revealing that thermal conductivity decreased with an increase in temperature consistently after annealing compared to that before annealing. A highest ZT of ~0.043 at 723 K was obtained, which is 8 times of that of undoped ZnO. Our study demonstrates the feasibility of CaO-doped ZnO as a potential TE material. |
| format | Article |
| id | doaj-art-acd2adf751ff437a867ff1518b31a3b4 |
| institution | DOAJ |
| issn | 2692-7640 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | American Association for the Advancement of Science (AAAS) |
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| series | Energy Material Advances |
| spelling | doaj-art-acd2adf751ff437a867ff1518b31a3b42025-08-20T02:43:06ZengAmerican Association for the Advancement of Science (AAAS)Energy Material Advances2692-76402025-01-01610.34133/energymatadv.0140Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal OxideXiaosong Tang0Sheau Wei Chien1Qiang Zhu2Zhengyao Qu3Jianwei Xu4Xizu Wang5Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore.Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore.Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore.State Key Laboratory of Silicate Materials for Architectures, Wuhan University of Technology, Wuhan 430070, China.Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore.Institute of Materials Research and Engineering (IMRE), Agency for Science, Technology and Research (A*STAR), Singapore 138634, Singapore.Active metals such as calcium (Ca)-doped zinc oxide (ZnO)-based thermoelectric (TE) materials are less studied in the literature, primarily due to the expected inherent instability caused by surface hydration. In this work, we synthesized Ca-doped ZnO-based composites (Zn(1−x)CaxO) by doping ZnO with CaO nanoparticles using the spark plasma sintering method (0.05 to 0.2 mol. %) and subsequently investigated the TE properties of these Zn(1−x)CaxO composites. Unlike well-known Al- or Ga-doped ZnO composites, Zn(1−x)CaxO exhibited a different behavior from Al- or Ga-doped ZnO. The electrical conductivity of Zn(1−x)CaxO was much improved from being nonconductive to being conductive, achieving an electrical conductivity of 650 S cm−1 when doping with 0.1 mol. % CaO. This improvement is due to the surface hydration of hygroscopic CaO, which forms conductive Ca(OH)2, enhancing the electrical conductivity. However, the electrical conductivity was remarkably decreased after Zn(1−x)CaxO was subjected to annealing at 860 K. In contrast, the Seebeck coefficient, ranging from −90 to −160 μV K−1, was not substantially affected by the high-temperature annealing process, indicating that part of Zn2+ ions were substituted with Ca2+ ions during annealing. Zn(1−x)CaxO composites were studied by x-ray diffraction and x-ray photoelectron spectroscopy. It was found that Zn(1−x)CaxO exhibited a crystal structure similar to that of ZnO. X-ray photoelectron spectroscopy results showed that there are 2 different types of Ca2+ ions in the Zn(1−x)CaxO composites. One type is assigned to Ca2+ ions that substituted for Zn2+ ions in the ZnO lattice, while the other type is Ca2+ ions from nonelectrically conductive free CaO. The temperature-dependent thermal conductivity of ZnO0.99CaO0.01 before and after annealing was examined, revealing that thermal conductivity decreased with an increase in temperature consistently after annealing compared to that before annealing. A highest ZT of ~0.043 at 723 K was obtained, which is 8 times of that of undoped ZnO. Our study demonstrates the feasibility of CaO-doped ZnO as a potential TE material.https://spj.science.org/doi/10.34133/energymatadv.0140 |
| spellingShingle | Xiaosong Tang Sheau Wei Chien Qiang Zhu Zhengyao Qu Jianwei Xu Xizu Wang Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide Energy Material Advances |
| title | Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide |
| title_full | Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide |
| title_fullStr | Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide |
| title_full_unstemmed | Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide |
| title_short | Enhancement of Thermoelectric Properties of Zinc Oxide Composites via Doping with Active Metal Oxide |
| title_sort | enhancement of thermoelectric properties of zinc oxide composites via doping with active metal oxide |
| url | https://spj.science.org/doi/10.34133/energymatadv.0140 |
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