Characterization of LiFeCl4 and AgFeCl4 ionic conductors

LiFeCl4 and AgFeCl4 are obtained by direct reaction between LiCl or AgCl and FeCl3 at 300°C and 400°C respectively. Both compounds are monoclinic with a = 7.02 (1) Å, b = 6.33 (1) Å, c = 12.72 (4) Å, β = 92° (30') for LiFeCl4 and a = 10.60 (5) Å, b = 6.30 (5) Å, c = 12.34 (10) Å, β = 106° (1) for AgFeCl4.LiFeCl4 is clearly isotypic of LiAlCl4. Magnetic measurements characterize in both cases Fe3+ ions in a high spin tetrahedral situation. LiFeCl4 becomes antiferromagnetic at low temperature (TN≅10 K). AgFeCl4 reveals a more complex situation. On contrary to the silver derivative, LiFeCl4 is a good ionic conductor with activation energy of 0.78 eV in the solid state below 105°C, and a sharp increase in the lithium mobility at this temperature.