Synthesis and characterisation of the new oxyfluoride Li+ ion conductor, Li5SiO4F

Inglis, Kenneth and Blanc, Frederic (2018) Synthesis and characterisation of the new oxyfluoride Li+ ion conductor, Li5SiO4F. [Data Collection]

Collection description

A new polymorphic phase, Li5SiO4F, with Li+ ion dynamics that are structurally distinct from Li4SiO4, is described. The γ polymorph forms at 750-775 °C, melts incongruently at 800 oC and crystallizes in a monoclinic unit cell: a = 8.67(1) (Å), b = 16.51(1) (Å), c = 11.23(2) (Å), β = 96.61(4) (o) and V = 1602.3(3) (Å3). The α polymorph forms at 650 oC appears to be metastable. The γ polymorph has a Li+ ion conductivity of 1.2x10-7 Scm-1 at 40 oC, that is several orders of magnitude higher than both the α polymorph and Li4SiO4, with an associated activation energy of 0.51(1) eV. Variable temperature 19F and 7Li static NMR measurements show the absence of F- mobility but the existence of Li+ mobility and confirm that Li+ is the ionic charge carrier in in both polymorphs of Li5SiO4F. 7Li line narrowing NMR experiments suggest that the barrier to local Li hopping is fairly small (0.2-0.3 eV) with faster Li+ ion dynamics in γ-Li5SiO4F compared to α-Li5SiO4F. γ-Li5SiO4F has negligible electronic conductivity, is stable in contact with Li metal and is a new type of stoichiometric, mixed anion, Li+ ion conductor.

Keywords: Lithium conductivity, Li silicate, solid state NMR
Divisions: Faculty of Science and Engineering > School of Physical Sciences
Depositing User: Kenneth Inglis
Date Deposited: 25 Oct 2018 15:02
Last Modified: 25 Oct 2018 15:02

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