For the preparation of the La2Ni0.75Co0.25O4.08 cathode composite, 30 wt-% of as-synthesized La2Ni0.75Co0.25O4.08 was mixed with 60 wt-% of La0.9Ba0.1F2.9 and 10 wt-% of dried carbon black to improve the ionic and electronic conductivity of the cathode material. The mixture was then ball milled for 3 hrs at the rotational speed of 250 rpm. BaSnF4 and PbSnF4 were synthesized by mechanochemical milling of stoichiometric ratios of BaF2 (Sigma Aldrich 99.99 %)/PbF2 (Alfa Aesar, 99 % min) and SnF2 (Sigma Aldrich, 99 %) and post annealing. Milling was conducted in 50 ml zirconia vials with zirconia balls under Argon atmosphere, and every 10 minute milling interval is followed by 20 minute break. For BaSnF4, 5 mm zirconia balls and a ball-to-powder ratio of 17:1 were used. After milling at 600 rpm for 12 hrs effective time the powder was annealed at 300 °C for 2 hrs in vacuum in an alumina crucible. The whole procedure is repeated three times to achieve high purity of the product. For PbSnF4, ten zirconia balls of 10 mm diameter were used during 12 hrs milling (370 rpm) for synthesizing 3 g of γ-PbSnF4. After milling, the powder was annealed at 200 °C in airtight stainless-steel containers under argon for 4 hrs.