Displacements in the cationic motif of nonstoichiometric fluorite phases Ba{sub 1-x}R{sub x}F{sub 2+x} as a result of the formation of {l_brace}Ba{sub 8}[R{sub 6}F{sub 68-69}]{r_brace} clusters: I. The Ba{sub 0.78}Tm{sub 0.22}F{sub 2.22} crystals
Journal Article
·
· Crystallography Reports
- Russian Academy of Sciences, Shubnikov Institute of Crystallography (Russian Federation)
The displacements of Ba{sup 2+} cations in the cationic motif of Ba{sub 0.78}Tm{sub 0.22}F{sub 2.22} crystals, which are representatives of nonstoichiometric fluorite phases Ba{sub 1-x}R{sub x}F{sub 2+x}, are proved for the first time with the use of precision investigations of the fine atomic structure. It is shown that the cation displacements, like the previously revealed displacements in the anionic motif, reflect the formation of {l_brace}Ba{sub 8}[R{sub 6}F{sub 68-69}]{r_brace} superclusters of structural defects with nanometer linear sizes. The Ba {sup 2+} cations are displaced from the fluorite crystallographic positions 4a (space group Fm3-barm) to the positions 32f. The static nature of the cation displacements is confirmed by the fact that these displacements are retained at a temperature of 110 K. The correctness of the interpretation of the correlation between the cation displacements and the formation of superclusters of structural defects is supported by the coincidence of the intercationic distances determined in the disordered phase Ba{sub 0.78}Tm{sub 0.22}F{sub 2.22} with those found in the previously studied ordered phases Ba{sub 4}R{sub 3}F{sub 17} (R = Y, Yb). The model with splitting of cationic positions is appropriate for testing in structural investigations of crystals of the fluorite phases M{sub 1-x}R{sub x}F{sub 2+x} at room temperature.
- OSTI ID:
- 22050897
- Journal Information:
- Crystallography Reports, Journal Name: Crystallography Reports Journal Issue: 6 Vol. 53; ISSN 1063-7745; ISSN CYSTE3
- Country of Publication:
- United States
- Language:
- English
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