Neutron diffraction study of the α- to β-phase transition in BaD2 under high pressure

Christopher J. Ridley, Nicholas P. Funnell, Craig L. Bull, Holger Kohlmann

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6 Scopus citations

Abstract

We report high-pressure neutron diffraction, and Raman spectroscopy data from the α- (Pnma) to β- (P63/mmc) phase transition in BaD2. The transition was observed at 2.53(5) GPa on pressure increase, and 1.65(5) GPa on pressure decrease, with a relatively narrow 0.20(5) GPa region of phase coexistence. We report the isothermal equations of state for the α-phase at 300 K and the β-phase at both 300 K and 480 K, and have calculated the entropy change through the transition. The Raman data show that a low-energy Ba vibration is seen to soften with applied pressure; DFT calculations suggest that this is predominantly due to an instability in the Ba atoms prior to the first-order transition. The shift in D positions in the high-pressure phase suggest that the Wyckoff 4f-model (where one of the D atoms is split between two sites) is a better fit at lower pressures, but that the model tends towards the Wyckoff 2d-model (where D1 is localised on a single site) with increased pressure. These results are used to discuss implications on the reported increases in ionic-conductivity over the transition.

Original languageEnglish
Article number113965
JournalSolid State Communications
Volume318
DOIs
StatePublished - Sep 2020
Externally publishedYes

Keywords

  • Alkali-earth hydride
  • First-order transition
  • High-pressure
  • Ionic hydride
  • Neutron diffraction

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