Journal
INORGANIC CHEMISTRY
Volume 57, Issue 19, Pages 12093-12105Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.inorgchem.8b01665
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Funding
- CONACYT (Mexico) [CB2013-01-221701]
- MINECO (Spain) [MAT2016-78362-C4-1-R]
- USPCEU through SAIDRXMEB laboratory
- Energy Frontier Research Center Materials Science of Actinides - U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences [DE-SC0001089]
- DOE National Nuclear Security Administration (NNSA) [DE-NA0001974]
- DOE-BES [DE-FG02-99ER45775, DE-AC02-06CH11357]
- National Science Foundation
- U.S. DOE-NNSA through Carnegie DOE Alliance Center [DE-NA-0002006]
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Depending on intrinsic (e.g., radius ratio rule r(Ln)/r(Zr)) and extrinsic factors (e.g., processing conditions), pyrochlore-type Ln(2)Zr(2)O(7) oxides achieve variable degrees of structural disorder. We report on a systematic study of the structural and microstructural characteristics of the Gd(2-x)Ln(x)Zr(2)O(7) system, exploring the effect of replacing Gd with a wide range of homovalent lanthanide ions (Ln = Nd, Sm, Dy, Ho, Y, and Er; x = 0.20 and 0.80). All compositions were prepared via a mechanochemical reaction between the corresponding oxides and characterized by X-ray diffraction (standard and synchrotron sources) using the Rietveld method, as well as by Raman spectroscopy. Irrespective of chemical composition, this study reveals that all compositions exhibit a fluorite-like structure. Furthermore, by firing each sample at 800 and 1400 degrees C, we are able to analyze the transition to pyrochlore-like structures, featuring different degrees of disorder, in all but Gd1.20Y0.80Zr2O7) which retains the fluorite structure even after heating. The structural data are used to assess the existing criteria for predicting the formation and stability of the pyrochlore structure; according to this analysis, the simple radius ratio rule (r(Ln)/r(Zr)), provides a useful and sufficiently robust criterion. Because the pyrochlore structure has a strong tendency to disorder, it is not possible to define an empirical index similar to the Goldschmidt tolerance factor for perovskite.
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