 (Small) changes in the Y and/or Li site-occupancies may affect the ionic conductivity  Finally, there are reports that the increase in configurational entropy in mixed (poly)anion substituted samples may alter the ionic conductivity While it is not possible to deconvolute these factors based on the data presented here, some general observations can be made. First of all, if the increase in ionic conductivity due to the larger lattice polarizability was the only/main factor at play, the activation energy should decrease monotonically with x, which is not the case. A similar argument can be made for the configurational entropy, if it was the only/main factor at play the maximum in ionic conductivity should be found at x=3 in Li3YBrxCl6-x.The trigonal phase has much higher activation energies (0.685 eV for x=0, 0.413 eV for x=1.5) compared to the monoclinic phase (0.300 eV for x=3, 0.276 eV for x=4.5, 0.330 eV for x=6), it is therefore rather likely that the ccp-like packing is more favourable, as also postulated theoretically in literature for sulphides (where, however, Li preferentially resides in tetrahedral coordination) . Considering the large change in ionic conductivity from Li3YCl6 to Li3YBr1.5Cl4.5, it is likely that the increase of the lattice parameters aids the conductivity in the 𝑃3 ̅ 𝑚1 phase. To investigate the effect of site occupancies, more compositions should be considered and x-ray diffraction data should be refined simultaneously with the neutron diffraction data for more accurate site occupancies.