A Raman spectroscopic and energy-dispersive x-ray diffraction study of the high-pressure phase transitions of sodium hydrogen fluoride

A. G. Christy*, J. Haines, S. M. Clark

*Corresponding author for this work

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9 Citations (Scopus)

Abstract

Under ambient conditions, NaHF2 adopts a rhombohedral structure. Two high-pressure phase transitions have been noted previously, which the authors have located at 5 kbar and 41 kbar. They have studied all three phases by Raman spectroscopy and energy-dispersive X-ray diffraction. The symmetric (FHF) stretching vibration is at a significantly higher frequency in phase I (631 cm-1 at ambient) than in phase II (623 cm-1 and 612 cm-1 at 10.6 kbar). The phase I structure is also incompressible down the triad axis, along which the (FHF) groups are oriented. The phase II X-ray data were fitted by a monoclinically distorted marcasite-like cell. This structure is easily derived from that of phase I by a shear, with accompanying rotation of the (FHF) groups into two distinct orientations consistent with the observed splitting of the Raman modes. A further 5% volume discontinuity occurs at the II-III transition. The diffraction data for phase III index on a tetragonal cell whose dimensions suggest a variant of the structure adopted by KHF2 at ambient pressure.

Original languageEnglish
Article number008
Pages (from-to)8131-8140
Number of pages10
JournalJournal of Physics: Condensed Matter
Volume4
Issue number41
DOIs
Publication statusPublished - 1992
Externally publishedYes

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