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 I4/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 I4/mcm structure shared by the heavier alkali metal bifluorides and γ-NaN3.
CITATION STYLE
Millar, D. I. A., Barry, C., Marshall, W. G., & Pulham, C. R. (2014). Structural characterization of sodium azide and sodium bifluoride at high pressures. Zeitschrift Fur Kristallographie, 229(3), 259–275. https://doi.org/10.1515/zkri-2013-1660
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