The low-temperature form of Rb2KCrF6 and Rb2KGaF6: The first example of an elpasolite-derived structure with pentagonal bipyramid in the B-sublattice
ZÚÑIGA, Francisco Javier
Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología
Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología
ZÚÑIGA, Francisco Javier
Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología
< Reduce
Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología
Language
en
Article de revue
This item was published in
Journal of Solid State Chemistry. 2006, vol. vol. 179, n° 12, p. p. 3607-3614
Elsevier
English Abstract
The crystal structure of the low-temperature forms of Rb2KCrF6 and Rb2KGaF6 has been solved on single crystal. The symmetry is tetragonal with F4/m space group; the unit cell parameters are: a=19.407 (3) Å, c=8.833 (2) Å ...Read more >
The crystal structure of the low-temperature forms of Rb2KCrF6 and Rb2KGaF6 has been solved on single crystal. The symmetry is tetragonal with F4/m space group; the unit cell parameters are: a=19.407 (3) Å, c=8.833 (2) Å for Rb2KCrF6 at T = 90 K and a=19.375 (4) Å, c=8.782 (2) Å for Rb2KGaF6 at T = 90 K. The relationships between the parameters of the prototype cubic elpasolite, which is stable at high temperature, and the tetragonal superlattice of the low temperature form have been established. Considering the general formulation A2BB′F6, the cationic positions in the A and (B,B′) sublattices remain identical in the two allotropic varieties. The main originality of the structure concerns the environment of 4/5 of the potassium atoms (B sublattice) which is transformed from octahedra into pentagonal bipyramids sharing edges with adjacent B′F6 octahedra containing Cr or Ga. The displacive phase transition is simply explained by the rotation of 45° in the (a,b) plane of 1/5 of the B′F6 (B′=Cr, Ga) octahedra. The similarity of this phase transition and the transformation of perovskite into tetragonal tungsten bronze (TTB) will be discussed.Read less <
English Keywords
Perovskite
Elpasolite
Fluorides
Complex compounds
Pentagonal bipyramid
Crystal structure
Phase transitions
Structural chemistry
Origin
Hal imported