Structural characterization of sodium azide and sodium bifluoride at high pressures

David I. A. Millar, Christopher Barry, William G. Marshall, Colin R. Pulham*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

This paper reports the structural characterization of sodium azide and sodium bifluoride (hydrogenfluoride) at elevated pressures using neutron powder diffraction. Compression of sodium azide at 294 K induces a transition from the β-phase to the α-phase. This structure responds to increasing pressure by progressive tilting of the azide groups. Compression of the α-form to 3.33 GPa at 393 K results in a phase transition to the tetragonal γ-phase (space group I14/mcm), which is isostructural with the azides of the heavier Group 1 elements and features square-antiprism co-ordination of the cations. On decompression at ambient temperature, the γ-phase reverts to the α-phase, but with substantial peak broadening indicative of significant strain within the recovered sample. Compression of sodium bifluoride (NaDF2-I to 0.66 GPa at ambient temperature resulted in the formation of NaDF2-II, which adopts an orthorhombic, marcasite-like (space group Pnnm) structure. Further compression to 4.58 GPa resulted in a transition to NaDF2-III, which adopts the archetypal I14/mcm structure shared by the heavier alkali metal bifluorides and γ-NaN3.

Original languageEnglish
Pages (from-to)259-275
Number of pages17
JournalZeitschrift für Kristallographie
Volume229
Issue number3
Early online date13 Feb 2014
DOIs
Publication statusPublished - Mar 2014

Keywords

  • high pressure
  • azide
  • bifluoride
  • neutron diffraction
  • crystal structure
  • NEUTRON POWDER DIFFRACTION
  • X-RAY-DIFFRACTION
  • EQUATION-OF-STATE
  • PHASE-TRANSITION
  • CRYSTAL-STRUCTURES
  • HYDROGEN-BOND
  • METAL AZIDES
  • INORGANIC AZIDES
  • HEAT-CAPACITY
  • ALKALI

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