The initial cubic phase obtained after milling was observed to transform into a tetragonal structure following an annealing process, as shown in Figure (red pattern). The sharp reflections indicate good crystallinity of the annealed sample. The ionic conductivity of the annealed BaSnF4 calculated from the fitted total resistance in the fitted equivalent circuit is 3.5×10 -4 S cm -1 at 25 °C. Both phase structure and ionic conductivity of the annealed t-BaSnF4 are consistent with literature values for t-BaSnF4 . In Figure , the asymmetry of certain reflections (marked by blue vertical lines) at lower angles can be easily recognized. This asymmetric characteristic has been rarely noticed, where it was attributed to the remaining incorporated cubic-BaF2 and X-ray amorphous SnF2 or cubic-BaSnF4. However, simply adding starting materials and cubic-BaSnF4 into structure analysis gives a poor fit in our case. The reflections, which show the asymmetric tail at lower 2-theta values, are correlated to lattice planes which have a strong dependence on the c lattice parameter in a tetragonal unit cell, for example, reflections at around 25.8°, 43.4°, 49.4° and 52.8° corresponding to (102), (114), ( ) and (106). In contrast, (h k 0) reflections do not show such asymmetric characteristics.