New simultaneously doped pyrochlore compounds (Ca1−xCex)2(ZrxNb1−x)2O7 negative temperature coefficient ceramics

Zhang, Fan; Xie, Yongxin; Zhang, Huimin; Li, Haibing; Chen, Xianghui; Su, Zhi; Chang, Aimin

doi:10.1007/s10854-021-05689-w

Cited by 7 publications

(6 citation statements)

References 21 publications

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“…Figure displays the curve fitting results of the Ce 3d XPS peaks of the x = 0.14 specimen. As described in the literature, u′, v′, u 0 , and v 0 are the characteristic peaks of Ce 3+ while u‴, u″, u, v′′′, v′′, and v are attributed to Ce 4+ ions. The peak parameters are listed in Table .…”

Section: Resultsmentioning

confidence: 69%

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd₂Zr₂O₇

Shu

Wen

et al. 2022

Langmuir

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To safely dispose radioactive waste (including, e.g., thorium and radiostrontium), Ce4+ and Sr2+ were chosen as simulated surrogates of α and β waste and were introduced into the Gd3+ site in Gd2Zr2O7 to maintain the average cationic radius and to compensate for charge. A series of Gd2–x Sr x/2Ce x/2Zr2O7 (0.00 ≤ x ≤ 0.25) compounds were examined by experimental and theoretical calculations to investigate the co-doping effects of α and β waste in a Gd2Zr2O7-based matrix. The effects of Ce4+ and Sr2+ content on the phase, unit cell parameters, active modes, mechanical property, and microstructure were studied systematically. Moreover, the limit of incorporation of Ce4+ and Sr2+ in Gd2Zr2O7 pyrochlore and the lattice parameters were also calculated through virtual crystal approximation theory, and the results were found to well agree with experimental results.

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Section: Resultsmentioning

confidence: 69%

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd₂Zr₂O₇

Shu

Wen

et al. 2022

Langmuir

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“…When the molten slag cooled to 1593 K from 1673 K, the diffraction peak of Ca 2 Nb 2 O 7 (JCPDF:70‐2006) was confirmed. [ 33 ] The molten slag at 1573 K, part pf NaNbO 3 (JCPDF:75‐2102) appeared. But when the molten slag was at 1553 K, the diffraction peak of NaNbO 3 almost disappeared and calcium magnesium silicate (Ca 2 Mg(Si 2 O 7 )) existed.…”

Section: Resultsmentioning

confidence: 99%

The Isothermal and Non‐Isothermal Growth Behaviors of Ca₂Nb₂O₇ in Molten Slag

Han,

Ran,

Chen

et al. 2024

Cryst. Res. Technol.

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Calcium pyroniobate (Ca2Nb2O7) as a kind of lead‐free piezoelectric material has been applied for different fields, but the study of isothermal and non‐isothermal growth behaviors of Ca2Nb2O7 in the molten slag is infrequent. In this paper, the in situ thermal analyzer with a single hot thermocouple technique (SHTT) is used to study the growth behaviors of Ca2Nb2O7 in molten slag. In the isothermal temperatures, the Ca2Nb2O7 presents two kinds of growth morphology, including three dimensional (3D) rhombus growth and fibrous one dimensional (1D) growth. The 3D rhombus is grown under the range of 1608 to 1628 K. When the temperature further decreases to 1593 K, the growth behavior of Ca2Nb2O7 becomes fibrous in 1D. Growth velocity affected by the degree of supercooling may account for the phenomenon of two kinds of growth behaviors in different temperatures. In the non‐isothermal growth process, the cooling rate over 10 K min−1 contributes to multiple crystal nucleuses growth of Ca2Nb2O7. The cooling rate below 5 K min−1 leads to single nuclear growth. This paper provides a control guideline for Ca2Nb2O7 growth.

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“…In this work, the XPS results confirm the valence change from Ce 4+ to Ce 3+ . This change may origin from the reaction of Ce with some of the oxygen vacancies in pyrochlore, reducing tetravalent cerium ions to trivalent while releasing oxygen 35 . The reaction is shown in the following formula:

\begin{equation}{\mathrm{2C}}{{\mathrm{e}}}_{{\mathrm{Ce}}} + {\mathrm{O}}_{\mathrm{O}}^{\mathrm{ \times }} \to {\mathrm{2Ce^{\prime}}}_{{\mathrm{Ce}}} + V_{\mathrm{O}}^{ \cdot \cdot } + \frac{{\mathrm{1}}}{{\mathrm{2}}}{{\mathrm{O}}}_{\mathrm{2}}\end{equation}

…”

Section: Discussionmentioning

confidence: 99%

“…This change may origin from the reaction of Ce with some of the oxygen vacancies in pyrochlore, reducing tetravalent cerium ions to trivalent while releasing oxygen. 35 The reaction is shown in the following formula: However, the gradual decrease of oxygen vacancy concentration inhibits the defect reaction, resulting in a decrease in the ratio of generated Ce 3+ to the whole Ce content. In addition, this is also one of the reasons for the transformation from the pyrochlore to the fluorite structure, and defect reaction causes the oxygen vacancies rearranged and becomes more disordered.…”

Section: Valence Statementioning

confidence: 99%

Free occupying mechanism of simulated tetravalent waste ions in Gd₂Zr₂O₇ and performance evaluation of the waste forms

Zuo

You

et al. 2023

J Am Ceram Soc.

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To extend the practicability of ceramics in immobilizing nuclear waste with fluctuant composition, structural design should be abandoned. The simulated tetravalent actinide waste An4+ (Ce4+) was directly doped into prepared Gd2Zr2O7, and the waste forms were synthesized by high‐temperature solid‐state reaction. It has been shown that the maximum loading of CeO2 in Gd2Zr2O7 lies between 20 and 30 wt.%, and Ce elements are uniformly distributed in the matrix. Existing in Ce3+ and Ce4+, cerium ions automatically occupied both the Gd and Zr sites in Gd2Zr2O7 according to valence equilibrium. This occupation causes the change of r(A3+)/r(B4+) and eventually leads to the structure transition from pyrochlore to fluorite. In addition, the normalized leaching rate of the sample with 60 wt.% of dopant was about 2.5 × 10−7 g m−2 d−1 on the 35th day. In this study, a free occupation of simulated waste ions in ceramics was proposed.

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New simultaneously doped pyrochlore compounds (Ca1−xCex)2(ZrxNb1−x)2O7 negative temperature coefficient ceramics

Cited by 7 publications

References 21 publications

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd₂Zr₂O₇

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd₂Zr₂O₇

The Isothermal and Non‐Isothermal Growth Behaviors of Ca₂Nb₂O₇ in Molten Slag

Free occupying mechanism of simulated tetravalent waste ions in Gd₂Zr₂O₇ and performance evaluation of the waste forms

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New simultaneously doped pyrochlore compounds (Ca1−xCex)2(ZrxNb1−x)2O7 negative temperature coefficient ceramics

Cited by 7 publications

References 21 publications

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd2Zr2O7

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd2Zr2O7

The Isothermal and Non‐Isothermal Growth Behaviors of Ca2Nb2O7 in Molten Slag

Free occupying mechanism of simulated tetravalent waste ions in Gd2Zr2O7 and performance evaluation of the waste forms

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Product

Resources

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Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd₂Zr₂O₇

Experimentally and Theoretically Revealing the Co-Doping Effects of Ce–Sr in Gd₂Zr₂O₇

The Isothermal and Non‐Isothermal Growth Behaviors of Ca₂Nb₂O₇ in Molten Slag

Free occupying mechanism of simulated tetravalent waste ions in Gd₂Zr₂O₇ and performance evaluation of the waste forms