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Abstract: Atomistic simulation methods were used to investigate the surface structures and stability of pyrolusite and ramsdellite polymorphs of electrolytic manganese dioxide (EMD). The interactions between the atoms were described using the Born model of Solids. This model was used to calculate the structures and energies of the low index surfaces {001}, {010}, {011}, {100}, {101} and {110} for both pyrolusite and ramsdellite. Pyrolusite is isostructural with rutile and similar to rutile the {110} surface is found to be the most stable with the relaxed surface energy 2.07Jm−2. In contrast, for ramsdellite the {101} surface is the most stable with a surface energy of 1.52Jm−2. Pyrolusite {100} and ramsdellite {100}b surfaces have equivalent energies of 2.43Jm−2 and 2.45Jm−2, respectively and similar surface areas and hence are the likely source for the intergrowths. Finally, comparison of the energies of reduction suggests that the more stable surfaces of pyrolusite are more easily reduced. [Copyright &y& Elsevier]

A combination of both Raman and Brillouin scattering experiments as well as Molecular Dynamics (MD) was used to study the superionic behaviour of BaF 2 doped with a wide range of LaF 3 concentrations (0 ⩽ x ⩽ 50 mol%). Raman spectroscopy reveals that for undoped BaF 2 and those doped with 5% and 10% LaF 3 , the room temperature spectra show the usual T 2g symmetry mode at 241 cm −1 whereas for those doped with 20%, 30% and 50% LaF 3 , the dominant Raman mode is of the E g symmetry situated at ∼263, 275 and 286 cm −1 , respectively. The Raman linewidths show near linear increases with temperature followed by rapid increases above the characteristic transition temperatures ( T c ), being at 1200, 850, 800, 975, 950 and 920 K for LaF 3 concentrations of 0, 5, 10, 20, 30 and 50; respectively. The temperature dependence of the squares of the Brillouin frequencies (Δ ω B ) 2 of the LA and TA acoustic modes respectively related to elastic constants C 11 and C 44 showed linear decreases followed by significant deviations around the same temperatures ( T c ), 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. [ABSTRACT FROM AUTHOR]