Higherature monoclinic α-SrHfF6, and isostructural α-SrZrF6: Associating Hf2F12 bipolyhedra and SrF8 snub disphenoids.

Laval, Jean-Paul,Mayet, Richard

, p. 229 - 235 (2018)

The structure of the higherature monoclinic variety α-SrHfF6 (strontium hafnium hexafluoride) [and of isostructural α-SrZrF6 (strontium zirconium hexafluoride)] associates Hf2F12 bipolyhedra and SrF8 snub disphenoids, forming zigzag twisted [SrF6]n layers. The distribution of the Hf and Sr polyhedra forms a three-dimensional framework which can be related to the family of anion-excess ReO3-related superstructures. α-SrHfF6 corresponds to a new ABX6 type and is compared to the other main families already described. A partial amorphization of this structure is observed in samples quenched from the melt.The crystal structure of α-SrHfF6 corresponds to a new structure type in the ABX6 series. It associates Hf2F12 bipolyhedra and SrF8 snub disphenoids, forming zigzag twisted [SrF6]n layers.

Avignant, D.,Mansouri, I.,Chevalier, R.,Cousseins, J. C.

, p. 121 - 127 (1981)

The reactions of silver, zirconium, and hafnium fluorides with liquid ammonia: Syntheses and crystal structures of Ag(NH3) 2F·2NH3, [M(NH3)4F 4]·NH3 (M = Zr, Hf), and (N2

Kraus, Florian,Baer, Sebastian A.,Fichtl, Matthias B.

, p. 441 - 447 (2009)

By reaction of the tetrafluorides MF4 or the ternary silver fluorides Ag3M2F14 (M = Zr, Hf) with dry liquid ammonia at -40°C, the pentaammoniates [M(NH3)4F 4]·NH3 (1,

Sr3ZrF10, a new type of anion-excess fluorite superstructure. Comparison with Pb3ZrF10 and Pb3HfF10. Influence on defect structure models of M1-xZrxF2+2x fluorite solid solutions

Laval, Jean-Paul

, (2022/02/14)

The triclinic P 1ˉ structure of Sr3ZrF10 derives from the fluorite MF2 type by accommodation of the anionic excess (MX2.50) in ZrF8 polyhedra, independent one from another but organized in double columns aligned along [01-1] axis. Contrary to the orthorhombic Cmcm Pb3ZrF10 which also comprises double columns of square antiprisms which are aligned along [001] axis, the successive ZrF8 polyhedra in a column of Sr3ZrF10 take two different orientations in order to decrease the steric constraints resulting from the lower size of Sr2+ compared to Pb2+. In complement, the structure of Pb3ZrF10 is redetermined and the structure of isostructural Pb3HfF10 is refined. A small defect, corresponding to the statistical reorientation of a small proportion of Zr(Hf)F8 polyhedra, in a way similar to that described in Sr3ZrF10, is observed for the first time in both Pb phases but is absent in the isotypic structure of Ba3HfF10 with a higher size Ba2+ cation. The possibility of similar reorientations of the ZrF8 polyhedra in the homologous Pb1-xZrxF2+2x anion excess fluorite solid solution is discussed in relation with the previous models of columnar clusters proposed for this solid solution from neutron diffraction experiments supported by ionic conductivity and 19F NMR measurements of the Pb1-xZrxF2+2x solid solution and of the Pb3ZrF10 ordered superstructure.

New heptafluorozirconates and -hafnates AIBIIZr(Hf) F7 (AI = Rb, Tl; BII = Ca, Cd) - Synthesis, structures, and structural relationships

Meddar, Lynda,El-Ghozzi, Malika,Avignant, Daniel

, p. 565 - 570 (2009/03/12)

Four new ABZrF7 heptafluorozirconates (A = Rb, Tl; B = Ca, Cd) and their homologous heptafluorohafnates, all colorless, orthorhombic Cmcm (n°63), Z = 4, have been synthesized by heating stoichiometric mixtures of RbF or TlF, CaF2 or CdF2 and ZrF4 (HfF 4) in sealed platinum tubes at temperature ranging from 550°C (Tl) to 600°C (Rb). The crystal structures of both RbCdZrF7 and TlCdZrF7 have been solved from single-crystal X-rays diffraction data. Rietveld refinements were performed from X-rays powder patterns for RbCaZrF7 and TlCaZrF7. In this series of heptafluorides, both B2+ and Zr4+ cations exhibit a pentagonal bipyramidal 7-coordination. Their structural relationships with other heptafluorozirconates AIBIIZrF7 as well as β-KYb 2F7 are discussed. RbCaZrF7: a = 6.863(1) A, b = 11.130(1) A, c = 8.485(1) A; TlCaZrF7: a = 6.868(1) A b = 11.165(1) A, c = 8.486(1) A; RbCdZrF 7: a = 6.780(1) A, b = 11.054(4) A, c = 8.420(4) A; TlCdZrF7: a = 6.784(3) A b = 11.099(2) A, c = 8.424(9) A.