Light scattering and computer simulation studies of superionic pure and La-doped BaF2

[Display omitted] •Superionic behaviour of BaF2 with different LaF3 concentrations is reported.•Raman and Brillouin scattering with Molecular Dynamics (MD) are used.•Raman line-widths increase and Brillouin frequencies decrease in the respective superionic phases.•These correlate with the increases...

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Bibliographic Details
Published in:	Chemical physics Vol. 467; pp. 6 - 12
Main Authors:	Rammutla, K.E., Comins, J.D., Erasmus, R.M., Netshisaulu, T.T., Ngoepe, P.E., Chadwick, A.V.
Format:	Journal Article
Language:	English
Published:	Elsevier B.V 01-03-2016
Subjects:	Fluorites Light scattering spectroscopy Molecular Dynamics simulations Superionic conductors Molecular Dynamics simulations Fluorites Light scattering spectroscopy Superionic conductors
Online Access:	Get full text
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Summary:	[Display omitted] •Superionic behaviour of BaF2 with different LaF3 concentrations is reported.•Raman and Brillouin scattering with Molecular Dynamics (MD) are used.•Raman line-widths increase and Brillouin frequencies decrease in the respective superionic phases.•These correlate with the increases of the diffusion coefficients determined from MD. A combination of both Raman and Brillouin scattering experiments as well as Molecular Dynamics (MD) was used to study the superionic behaviour of BaF2 doped with a wide range of LaF3 concentrations (0⩽x⩽50mol%). Raman spectroscopy reveals that for undoped BaF2 and those doped with 5% and 10% LaF3, the room temperature spectra show the usual T2g symmetry mode at 241cm−1 whereas for those doped with 20%, 30% and 50% LaF3, the dominant Raman mode is of the Eg symmetry situated at ∼263, 275 and 286cm−1, respectively. The Raman linewidths show near linear increases with temperature followed by rapid increases above the characteristic transition temperatures (Tc), being at 1200, 850, 800, 975, 950 and 920K for LaF3 concentrations of 0, 5, 10, 20, 30 and 50; respectively. The temperature dependence of the squares of the Brillouin frequencies (ΔωB)2 of the LA and TA acoustic modes respectively related to elastic constants C11 and C44 showed linear decreases followed by significant deviations around the same temperatures (Tc), at which the Raman linewidths start to show substantial increases. The complementary studies using MD simulations show that the diffusion coefficients increase markedly above the same temperatures observed experimentally. The extrinsic fluorine ion trajectories were also determined from the MD simulations to better understand the mechanisms of diffusion.
ISSN:	0301-0104
DOI:	10.1016/j.chemphys.2015.12.004