Flash defect-engineering of oxygen-deficient zirconia

With the ever-increasing demand for energy and concerns about the environment and climate, intensive studies have been conducted to develop new materials for light absorption and photocatalytic applications. Owing to good physicochemical properties, zirconia has promising application in the field of photocatalysis. However, the wide band gap of zirconia enables it to absorb only ultraviolet light, resulting in the low efficiency in solar energy harvesting. Introduction of oxygen vacancies through doping and partial reduction has been demonstrated to be an effective method to reduce the band gap of metal oxide. Nevertheless, it is challenging to generate oxygen vacancies in zirconia because of the high oxygen vacancy formation energy. Thus, some more drastic conditions are employed to prepare the oxygen-deficient zirconia. However, the preparation processes are complicated and drastic processing conditions such as high temperature and pressures are required, which are not conducive to industrial production.  

Recently, a team of material scientists led by Xinghua Su from Chang’an University, China first reported the rapid fabrication of oxygen-deficient zirconia by flash sintering treatment. This work not only rapidly prepares the oxygen-deficient zirconia with excellent optical absorption capability and remarkable photocatalytic activity, but also offers a new tool to manipulate defects and properties in ceramics.

The team published their work in Journal of Advanced Ceramics on September 23, 2024.

“In this report, we fabricated the oxygen-deficient zirconia bulks in a very short time of 90 s by the flash sintering treatment at furnace temperature of 568 ℃ under a DC electric field of 150 V/cm. The introduction of oxygen vacancies into zirconia bulks through flash sintering treatment was confirmed using EPR and XPS techniques.” said Xinghua Su, professor in School of Materials Science and Engineering at Chang’an University, whose research interests mainly focus on the flash sintering of ceramics.  

“We found that oxygen vacancies were introduced into zirconia bulks through electrochemical reduction reactions. The color of sample completely turned from white to black due to the reduced band gap. Moreover, we found that the oxygen-deficient zirconia bulks exhibited the excellent optical absorption capability and remarkable photocatalytic activity.” said Xinghua Su.

After the flash sintering treatment, the direct band gap of zirconia was decreased from 4.18 eV to 2.09 eV, while the indirect band gap was decreased from 2.85 to 1.67 eV. “The introduction of oxygen vacancies into zirconia leaded to the generation of mid-gap states between the valence and conduction bands. Consequently, the band gap of oxygen-deficient zirconia was narrowed.” said Xinghua Su.

“Flash sintering treatment is a simple and cost-efficient approach for rapidly fabricating oxygen-deficient zirconia with high concentration of oxygen vacancies, which can also be applied to other materials.” said Xinghua Su.

However, more delicate research works are still needed to explore the flash sintering treatment as a new tool to design and engineer ceramics in the next future. It is expected the mechanical properties of ceramics can also be improved by the flash sintering treatment.

Other contributors include Wenjin Li, Shuai Zhang, Chengguang Lou, Peng Zhao from the School of Materials Science and Engineering at Chang’an University in Xi’an, China; Qiang Tian from the State Key Laboratory of Environment-Friendly Energy Materials at Southwest University of Science and Technology in Mianyang, China; Da Chen from the School of Energy and Environment at Southeast University, in Nanjing, China; Jianguo Zhao from the School of Physics and Electronic Information at Luoyang Normal University in Luoyang, China.

This work was supported by the Natural Science Foundation of China (grant No. 52472064 and 12305298), the Open Project of State Key Laboratory of Environment-friendly Energy Materials (grant No. 23kfhg06), the Sichuan Science and Technology Program (grant No. 2022JDTD0017), and the Natural Science Foundation of Jiangsu Province (grant No. SBK2023040604).

About Author

Dr. Xinghua Su is a professor in the School of Materials Science and Engineering at Chang’an University. He received Ph.D. in Materials Physics and Chemistry from Lanzhou University. He was a visiting scientist in the Cullen College of Engineering at University of Houston. His main research interests include high-entropy ceramics, nanomaterials, and flash sintering. He has authored and co-authored more than 70 peer-reviewed papers. He holds 6 Chinese patents and has presented over 10 invited talks in international academic conferences. He is a member of Chinese Materials Research Society (C-MRS), and Editorial Board Member of Journal of Advanced Ceramics. 

Miss Wenjin Li is a Mater degree candidate of School of Materials Science and Engineering at Chang’an University. Her research focuses on manipulation of microstructure of ceramics through flash sintering treatment.

About Journal of Advanced Ceramics

Journal of Advanced Ceramics (JAC) is an international academic journal that presents the state-of-the-art results of theoretical and experimental studies on the processing, structure, and properties of advanced ceramics and ceramic-based composites. JAC is Fully Open Access, monthly published by Tsinghua University Press, and exclusively available via SciOpen. JAC’s 2023 IF is 18.6, ranking in Top 1 (1/31, Q1) among all journals in “Materials Science, Ceramics” category, and its 2023 CiteScore is 21.0 (top 5%) in Scopus database. ResearchGate homepage: https://www.researchgate.net/journal/Journal-of-Advanced-Ceramics-2227-8508

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