Abstract
The defect structure of as grown Sr0.72Pr0.28F2.28, Sr0.87Tb0.13F2.13, Sr0.88Dy0.12F2.12, Sr0.89Ho0.11F2.11, and Sr0.9R0.1F2.1 single crystals (R = Y, Er, Tm, Yb) prepared under identical conditions has been studied by X-ray diffraction analysis. All crystals belong to the CaF2 structure type (sp. gr. \(Fm\bar {3}m\)) and have vacancies in the main anion motif and interstitial fluorine anions at site 32f in the crystal with R = Pr and site 48i for the other R. Interstitial fluorine anions are found near site 4b in the crystals with R = Tb and Dy (sites 32f and 24e, respectively) and at site 4b in the crystal with R = Er. Relaxation (static displacement of some main anions to site 32f) is observed in all crystals (except for R = Tb). Displacements of some Sr2+ cations to sites 32f and 24e is simultaneously observed in crystals with R = Tb, Dy, Tm, and Yb. In crystals with R = Ho, Y, and Er, some Sr2+ cations are displaced only to site 32f; no cation displacement is observed for R = Pr. A model of the defect structure of the phases is proposed based on the structure of crystals studied, according to which interstitial fluorine anions and R3+ cations are aggregated into [Sr4–nRnF26] clusters of tetrahedral configuration for the phase with R = Pr or [Sr14–nRnF64+n] clusters of octacubic configuration for other R.
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ACKNOWLEDGMENTS
This study was performed using the equipment of the Center of Collective Use of the Federal Scientific Research Centre “Crystallography and Photonics” of the Russian Academy of Sciences.
Funding
This study was supported by the Russian Foundation for Basic Research, project nos. 17-00-00118 and 19-02-00877, in the part concerning the optimization of techniques for growing single crystals and by the Ministry of Science and Higher Education of the Russian Federation within a State assignment (project no. RFMEFI62119X0035) in the part concerning the analysis of the structural characteristics of crystalline samples.
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Translated by A. Sin’kov
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Sulyanova, E.A., Karimov, D.N. & Sobolev, B.P. Nanostructured Crystals of Fluorite Phases Sr1–xRxF2+x (R Are Rare-Earth Elements) and Their Ordering. 16: Defect Structure of the Nonstoichiometric Phases Sr1–xRxF2+x (R = Pr, Tb–Yb) As Grown. Crystallogr. Rep. 65, 560–565 (2020). https://doi.org/10.1134/S1063774520040215
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DOI: https://doi.org/10.1134/S1063774520040215