Perovskite-like K3TiOF5Exhibits (3 + 1)-Dimensional Commensurate Structure Induced by Octahedrally Coordinated Potassium Ions

Fenghua Ding, Nenian Charles, Jaye K. Harada, Christos D. Malliakas, Chi Zhang, Roberto Dos Reis, Kent J. Griffith, Matthew L. Nisbet, Weiguo Zhang, P. Shiv Halasyamani, Vinayak P. Dravid, James M. Rondinelli, Kenneth R. Poeppelmeier*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Elpasolite- and cryolite-type oxyfluorides can be regarded as superstructures of perovskite and exhibit structural diversity. While maintaining a similar structural topology with the prototype structures, changes in the size, electronegativity, and charge of cation and/or anion inevitably lead to structural evolution. Therefore, the nominal one-to-one relation suggested by a doubled formula of perovskite does not guarantee a simple 2-fold superstructure for many cases. Herein, the commensurately modulated perovskite-like K3TiOF5 was refined at 100 K from single-crystal X-ray diffraction data by using a pseudotetragonal subcell with lattice parameters of a = b = 6.066(2) Å and c = 8.628(2) Å. The length of the modulation vector was refined to 0.3a∗ + 0.1b∗ + 0.25c*. In the commensurate supercell of K3TiOF5, the B-site Ti4+ and K+ cations in [TiOF5]3- and [KOF5]6- octahedral units were found to be significantly displaced from the average atomic positions refined in the subcell. The displacements of the K+ cations are ±0.76 Å, and those for the Ti4+ cations are approximately ±0.13 Å. One- and two-dimensional solid-state 19F NMR measurements revealed two tightly clustered groups of resonances in a ratio of ca. 4:1, assigned to equatorial and axial fluorine, respectively, consistent with local [TiOF5]3- units. S/TEM results confirmed the average structure. Electronic structure calculations of the idealized I4mm subcell indicate the instability to a modulated structure arises from soft optical modes that is controlled by the octahedrally coordinated B-site potassium ions in the cryolite-type structure.

Original languageEnglish (US)
Pages (from-to)18907-18916
Number of pages10
JournalJournal of the American Chemical Society
Volume143
Issue number45
DOIs
StatePublished - Nov 17 2021

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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