The Yttrium, Lanthanum, and Lanthanide Trifluorides: Internal Periodicity of Phase Transitions
- Authors: Sobolev B.P.1
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Affiliations:
- Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,” Russian Academy of Sciences
- Issue: Vol 64, No 5 (2019)
- Pages: 713-723
- Section: Crystal Chemistry
- URL: https://journals.rcsi.science/1063-7745/article/view/194176
- DOI: https://doi.org/10.1134/S1063774519050183
- ID: 194176
Cite item
Abstract
Internal periodicity of phase transitions (fusion and polymorphism) has been revealed in trifluorides of Y, La, and 14 lanthanides. This periodicity is determined by the internal periodicity of filling of the 4f-electron subshell of rare-earth elements (REEs, R), in which cerium 58Се–64Gd and terbium 65Тb–71Lu subsets can be selected. The lanthanide compression of ionic radii R3+ (15% towards the smaller one) induces the formation of three structure types: LaF3, β-YF3, and α-YF3 (α-UO3). The formula volumes Vform of REE trifluorides of the LaF3 and β-YF3 structure types only partially obey the internal periodicity of lanthanides with an increase in Z. The internal periodicity of the fusion and polymorphism of REE trifluorides (without ScF3) divides RF3 into four structural subgroups: A (R = La–Nd), B (R = Pm–Gd), C (R = Tb–Ho), and D (R = Er–Lu, Y), strictly specifying the percentage and elemental composition of each subgroup. The periodicity of the RF3 polymorphism in the products manifests itself in the crystallization of the melts prone to supercooling in the form of a periodic change of single crystals with coarse- or fine-grained blocks of the low-temperature forms.
About the authors
B. P. Sobolev
Shubnikov Institute of Crystallography, Federal Scientific Research Centre “Crystallography and Photonics,”Russian Academy of Sciences
Author for correspondence.
Email: sobolevb@yandex.ru
Russian Federation, Moscow, 119333