Defect Structure and Oxide Ion Conduction of Potassium Ion Substituted CaWO4
1
Graduate School of Energy Science, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan
2
Graduate School of Engineering, Tottori University, Koyama-cho Minami, Tottori 680-8552, Japan
3
Laboratory for Materials and Structures, Tokyo Institute of Technology, Nagatsuta-Cho, Midori-ku, Yokohama 226-8503, Japan
4
Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
5
National Institute of Technology, Kagawa College, Chokushi-cho, Takamatsu, Kagawa 761-8058, Japan
*
Author to whom correspondence should be addressed.
†
Takao Esaka has died in April, 2018.
Materials 2018, 11(7), 1092; https://doi.org/10.3390/ma11071092
Received: 25 May 2018
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Revised: 16 June 2018
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Accepted: 19 June 2018
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Published: 27 June 2018
(This article belongs to the Section Energy Materials)
We have prepared Ca1−xKxWO4−x/2 solid solutions with the Scheelite-type structure to investigate high-temperature electrochemical properties. Room-temperature X-ray diffraction suggested the solid solution range was x ≤ 0.2, since the second phase presumably of K2WO4 was detected for x = 0.3. For all the substituted samples up to x = 0.4, a large jump in conductivity has been observed around 500 °C. At higher temperatures, oxide ion conduction is found to be predominant even for x = 0.4, exceeding the solution limit estimated from the room-temperature XRD. The conductivity at high temperature is essentially proportional to the amount of substituted potassium ions up to x = 0.4, indicating that oxide ion conduction is associated with the formed oxide ion vacancy. High-temperature X-ray diffraction detected no apparent change in lattice parameters around 500 °C for x = 0.1, and the remaining second phase seems to be incorporated into the Scheelite lattice at high temperatures.
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Keywords:
CaWO4; oxide ion conductor; oxide ion vacancy; high-temperature XRD
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MDPI and ACS Style
Takai, S.; Shitaune, S.; Sano, T.; Kawaji, H.; Yabutsuka, T.; Esaka, T.; Yao, T. Defect Structure and Oxide Ion Conduction of Potassium Ion Substituted CaWO4. Materials 2018, 11, 1092. https://doi.org/10.3390/ma11071092
AMA Style
Takai S, Shitaune S, Sano T, Kawaji H, Yabutsuka T, Esaka T, Yao T. Defect Structure and Oxide Ion Conduction of Potassium Ion Substituted CaWO4. Materials. 2018; 11(7):1092. https://doi.org/10.3390/ma11071092
Chicago/Turabian StyleTakai, Shigeomi, Shinya Shitaune, Toshifumi Sano, Hitoshi Kawaji, Takeshi Yabutsuka, Takao Esaka, and Takeshi Yao. 2018. "Defect Structure and Oxide Ion Conduction of Potassium Ion Substituted CaWO4" Materials 11, no. 7: 1092. https://doi.org/10.3390/ma11071092
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