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Title: Pressure-induced structural changes in NH{sub 4}Br

We report angle dispersive X-ray diffraction (XRD) measurements and Raman spectroscopy on NH{sub 4}Br up to 70.0 GPa at room temperature. Three thermodynamically stable phases (phases II, IV, and V) are confirmed and a new possible phase (phase VI) of P2{sub 1}/m symmetry is proposed whose structure was established from Rietveld refinement of synchrotron XRD data for the first time. The phase sequence observed in NH{sub 4}Br is in accordance with phase II → IV → V → VI. Phase V transforms into phase VI at about 57.8 GPa with a huge volume reduction of 30%. Still, the intramolecular distances are analyzed to better understand the nature of structures. The H–H interactions become markedly more important as the N–Br distances are compacted, which is probably the reason of the kink of symmetric stretching band (ν{sub 1}) at the transition pressure.
Authors:
; ; ; ; ; ; ; ; ; ;  [1]
  1. State Key Laboratory of Superhard Materials, College of Physics, Jilin University, Changchun 130012 (China)
Publication Date:
OSTI Identifier:
22493512
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 6; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; AMMONIUM COMPOUNDS; BROMIDES; INTERMOLECULAR FORCES; MONOCLINIC LATTICES; PHASE STABILITY; PHASE STUDIES; PHASE TRANSFORMATIONS; PRESSURE RANGE GIGA PA; RAMAN SPECTROSCOPY; SYMMETRY; TEMPERATURE RANGE 0273-0400 K; X-RAY DIFFRACTION