TY - JOUR
T1 - Neutron diffraction study of the α- to β-phase transition in BaD2 under high pressure
AU - Ridley, Christopher J.
AU - Funnell, Nicholas P.
AU - Bull, Craig L.
AU - Kohlmann, Holger
N1 - Publisher Copyright:
© 2020 Elsevier Ltd
PY - 2020/9
Y1 - 2020/9
N2 - 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.
AB - 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.
KW - Alkali-earth hydride
KW - First-order transition
KW - High-pressure
KW - Ionic hydride
KW - Neutron diffraction
UR - http://www.scopus.com/inward/record.url?scp=85086076153&partnerID=8YFLogxK
U2 - 10.1016/j.ssc.2020.113965
DO - 10.1016/j.ssc.2020.113965
M3 - Article
AN - SCOPUS:85086076153
SN - 0038-1098
VL - 318
JO - Solid State Communications
JF - Solid State Communications
M1 - 113965
ER -