Structural characterization of new Tl+ and Pb2+ oxyfluoridozirconates deriving from hexagonal layer structures of M’xM3×9–13 general formula

Abstract

A new series of Tl⁺ and Pb²⁺ oxyfluoridozirconates is isolated and structurally described in hexagonal symmetry, P6₃/mmc space group and close lattice parameters (a = 7.649 Å and c = 15.797 Å for Tl_0.69Zr₃O_1.91F_8.87; a = 7.647(2) Å and c = 15.835(4) Å for Pb_0.714Zr₃O_2.90F_7.62). The refined Tl content varies from 0.69/1 to 0.90/1 (0.71 to 0.76 for Pb) and is never stoichiometric. Their structure corresponds to a stacking of hexagonal layers containing a strong framework of ZrOF₇ bicapped trigonal prisms and ZrO₂F₅ pentagonal bipyramids sharing edges and vertices and forming triangular clusters of formula comprised between Zr₃OF₁₈ and Zr₃O₄F₁₂. These units are all centered on one O anion and interconnected via F corners with three other triangular units forming layers delimiting holes of distorted hexagonal section partly occupied by Tl⁺ or Pb²⁺ cations.

This new type is compared to many structures presenting various stackings of similar hexagonal or pseudo-hexagonal layers with M³⁺ or M⁴⁺ cations of high size coordinated by 6, 7, 7 + 8, 8, 8 + 9, 9 F and/or O anions. All belong to a same family of phases of M’_xM₃X_9–13 general formula.