Defect Structures of La{sub 1–y}Sr{sub y}F{sub 3–y}, La{sub 1–y}Ba{sub y}F{sub 3–y}, and Nd{sub 1–y}Ca{sub y}F{sub 3–y} (y = 0.05, 0.10) Nonstoichiometric Tysonite Phases
Characteristic features of defect structures of La{sub 1–y}Sr{sub y}F{sub 3–y}, La{sub 1–y}Ba{sub y}F{sub 3–y}, and Nd{sub 1–y}Ca{sub y}F{sub 3–y} (y = 0.05, 0.10) nonstoichiometric phases of different compositions are determined from X-ray diffraction data. Interest in subtle details of their structure is determined by the possibility of ion transport over fluorine vacancies and by a strong compositional dependence of the ionic conductivity. The La{sub 0.95}Sr{sub 0.05}F{sub 2.95}, La{sub 0.95}Ba{sub 0.05}F{sub 2.95}, and Nd{sub 0.95}Ca{sub 0.05}F{sub 2.95} phases, as well as the La{sub 0.9}Ba{sub 0.1}F{sub 2.9} phase, crystallize as β-LaF{sub 3} (sp. gr. P3̅c1, Z = 6). The La{sub 0.9}Sr{sub 0.1}F{sub 2.9} and Nd{sub 0.9}Ca{sub 0.1}F{sub 2.9} phases lose their superstructure and are described by a cell whose volume is three times smaller (sp. gr. P6{sub 3}/mmc, Z = 2). Defects of crystal structure R{sub 1–y}M{sub y}F{sub 3–y} are not exhausted by vacancies in fluorine positions. All crystals with a “large” cell are twinned according to the merohedral twin law. The majority of atomic positions in models with a “small” cell are split by group symmetry elements and are occupied statistically.
- OSTI ID:
- 22758281
- Journal Information:
- Crystallography Reports, Vol. 63, Issue 1; Other Information: Copyright (c) 2018 Pleiades Publishing, Inc.; Country of input: International Atomic Energy Agency (IAEA); ISSN 1063-7745
- Country of Publication:
- United States
- Language:
- English
Similar Records
Defect structure and ionic conductivity of as-grown R{sub 1–y}Sr{sub y}F{sub 3–y} (R = Ce, Pr, or Nd) crystals with high SrF{sub 2} content
Mechanochemical synthesis of nonstoichiometric nanocrystals La{sub 1-y}Ca{sub y}F{sub 3-y} with a tysonite structure and nanoceramic materials from CaF{sub 2} and LaF{sub 3} crystals