Dropping from the highest pressure, the logarithm of the ionic conductivity increases linearly until it reaches a maximum. Past the maximum to lower pressures, a nonlinear decrease in the ionic conductivity is observed. A specific optimized stacking pressure for ionic conductivity, in the case of Ba0.6L0.4F2.4 and BaSnF4 around 250 MPa and for PbSnF4 around 500 MPa, can be noticed. For La0.9Ba0.1F2.9, only the linear region is observed without a second regime at low pressures. activation volumes, applying external pressure gives a hindrance to the unit cell expansion and therefore to the jump, and hence the ionic conductivity drops at high pressures. The drop of ionic conductivity at pressures below the maximum conductivity results from loss of contact at the pellet electrode interface and within the pellet itself. As mentioned in the experimental section, prior to the EIS measurements the electrolyte samples have been pelletized at 2 GPa which provides good compaction of the powder. It is reasonable to assume that there is no change in density of the pellet when the stack pressure is relieved in the linear regime. At pressures lower than the linear regime some crack formation happens due to elastic recovery of the pellet (detailed discussion is present in chapter 3.3). The different rates of dropping in ionic conductivity for different electrolytes in the low pressure regime are likely related to the physical properties of electrolytes such as different particle size and elastic