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Title: Polymorphic Transitions in Cerium-Substituted Zirconolite (CaZrTi 2O 7)

Compounds with the formulae CaZr 1–xCe xTi 2O 7 with x = 0.1–0.5 were synthesized by solid state reaction. Cerium was used as a surrogate for actinide elements. A transition from the 2M polymorph to the 4M polymorph (expanded unit cell due to cation ordering) in zirconolite was observed with increasing cerium content. The presence of both tri- and tetravalent Ce, contrary to formulation, was confirmed using X-ray absorption near edge spectroscopy, suggesting substitution on both Ca and Zr sites. Sintering was carried out via spark plasma sintering, during which the perovskite phase (Ca 0.4Ce 0.4TiO 3) was stabilized due to the reducing conditions of this technique. Scanning electron microscopy and energy dispersive spectrometry revealed that the 2M polymorph was dilute in Ce content in comparison to the 4M-zirconolite. High temperature X-ray diffraction was used to detail the kinetics of perovskite to zirconolite transition. It was found that CaCeTi 2O 7 (cubic pyrochlore) formed as an intermediate phase during the transition. Lastly, our results show that a transition from 2M- to 4M-zirconolite occurs with increasing Ce content and can be controlled by adjusting the P O2 and the heat treatment temperature.
Authors:
 [1] ;  [1] ;  [1]
  1. Alfred Univ., Alfred, NY (United States)
Publication Date:
Type:
Accepted Manuscript
Journal Name:
Scientific Reports
Additional Journal Information:
Journal Volume: 7; Journal Issue: 1; Journal ID: ISSN 2045-2322
Publisher:
Nature Publishing Group
Research Org:
Alfred University, Alfred, NY (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE
OSTI Identifier:
1393199

Clark, Braeden M., Sundaram, S. K., and Misture, Scott T.. Polymorphic Transitions in Cerium-Substituted Zirconolite (CaZrTi2O7). United States: N. p., Web. doi:10.1038/s41598-017-06407-5.
Clark, Braeden M., Sundaram, S. K., & Misture, Scott T.. Polymorphic Transitions in Cerium-Substituted Zirconolite (CaZrTi2O7). United States. doi:10.1038/s41598-017-06407-5.
Clark, Braeden M., Sundaram, S. K., and Misture, Scott T.. 2017. "Polymorphic Transitions in Cerium-Substituted Zirconolite (CaZrTi2O7)". United States. doi:10.1038/s41598-017-06407-5. https://www.osti.gov/servlets/purl/1393199.
@article{osti_1393199,
title = {Polymorphic Transitions in Cerium-Substituted Zirconolite (CaZrTi2O7)},
author = {Clark, Braeden M. and Sundaram, S. K. and Misture, Scott T.},
abstractNote = {Compounds with the formulae CaZr1–xCexTi2O7 with x = 0.1–0.5 were synthesized by solid state reaction. Cerium was used as a surrogate for actinide elements. A transition from the 2M polymorph to the 4M polymorph (expanded unit cell due to cation ordering) in zirconolite was observed with increasing cerium content. The presence of both tri- and tetravalent Ce, contrary to formulation, was confirmed using X-ray absorption near edge spectroscopy, suggesting substitution on both Ca and Zr sites. Sintering was carried out via spark plasma sintering, during which the perovskite phase (Ca0.4Ce0.4TiO3) was stabilized due to the reducing conditions of this technique. Scanning electron microscopy and energy dispersive spectrometry revealed that the 2M polymorph was dilute in Ce content in comparison to the 4M-zirconolite. High temperature X-ray diffraction was used to detail the kinetics of perovskite to zirconolite transition. It was found that CaCeTi2O7 (cubic pyrochlore) formed as an intermediate phase during the transition. Lastly, our results show that a transition from 2M- to 4M-zirconolite occurs with increasing Ce content and can be controlled by adjusting the PO2 and the heat treatment temperature.},
doi = {10.1038/s41598-017-06407-5},
journal = {Scientific Reports},
number = 1,
volume = 7,
place = {United States},
year = {2017},
month = {7}
}