- 著者
- Takeshi HAGIWARA Katsuhiro NOMURA Hiroyuki KAGEYAMA
- 出版者
- The Ceramic Society of Japan
- 雑誌
- Journal of the Ceramic Society of Japan (ISSN:18820743)
- 巻号頁・発行日
- vol.125, no.2, pp.65-70, 2017-02-01 (Released:2017-02-01)
- 参考文献数
- 20
- 被引用文献数
- 10 15
We synthesized Eu2Zr2O7 and La2Zr2O7 using high purity ZrO2 of extremely low Hf content. The crystal structures of Eu2Zr2O7 and La2Zr2O7 were refined by the Rietveld analysis of the powder X-ray diffraction data (indexed as a cubic pyrochlore-type structure, space group: No.227, Fd3m) measured from 1173 to 298 K in a dry condition and from 1173 to 323 K in a wet condition. The crystal structure of La2Zr2O7 is near to an ideal pyrochlore-type structure, whereas that of Eu2Zr2O7 is a distorted pyrochlore-type structure. The thermal expansion coefficients of Eu2Zr2O7 were larger than those of La2Zr2O7. The value of the equivalent isotropic atomic displacement parameters (Beq) calculated from the anisotropic atomic displacement parameter for the Zr in Eu2Zr2O7 at 298 K was around 1.4 Å2, and the increase of this value in Eu2Zr2O7 with increasing temperature was smaller than that in La2Zr2O7.
- 著者
- Takeshi HAGIWARA Hiroshi YAMAMURA Katsuhiro NOMURA Manabu IGAWA
- 出版者
- The Ceramic Society of Japan
- 雑誌
- Journal of the Ceramic Society of Japan (ISSN:18820743)
- 巻号頁・発行日
- vol.121, no.1410, pp.205-210, 2013-02-01 (Released:2013-02-01)
- 参考文献数
- 29
- 被引用文献数
- 20 22
Crystal structures of the Ln2Zr2O7 (Ln = Nd and La) were refined by the Rietveld analysis of powder neutron diffraction (ND) data at room temperature. La2Zr2O7 had a pyrochlore (P)-type structure of almost completely ordered for oxygen vacancy. On the other hand, Nd2Zr2O7 had the P-type structure for the oxygen vacancy distributed between the O2 (8b) and O3 (48f) sites. The Rietveld refinement results of powder X-ray diffraction (XRD) data of Ln2Zr2O7 (Ln = Eu, Nd and La) indicated that the Ln3+ and Zr4+ ions exist in ordered states in 16c and 16d sites, respectively. The refined lattice parameters (a), occupancies (g) for oxygen sites (O1, O2 and O3) and x-positional parameters for O3 (48f) site of La2Zr2O7 and Nd2Zr2O7 by using powder XRD data were in almost agreement with those by using powder ND data. The refined ND and XRD data of Ln2Zr2O7 (Ln = Eu, Nd and La) system revealed that the O3 (48f) site occupancy (g48f) decreases with increasing O2 (8b) site occupancy, while O1 (8a) site occupancy keeping 1.0. The change in oxide-ion conductivity (σ) in Ln2Zr2O7 (Ln = Eu, Nd and La) system can be related to a change in the product of site occupancy (g48f) and the oxygen vacancy rate (1-g48f) in the O3 (48f) site, g48f(1-g48f).