We can observe from the graph that aluminium- and magnesium doped
samples have better conductivity than the undoped counterpart.
As mentioned earlier, the role of iron on the conduction mechanism is
unclear, but they do have a positive influence on the conductivity. This
behaviour is in agreement with conductivity measurement results,
where it has been found that doping with aluminium (and magnesium)
leads to an increased ionic conductivity of the ATLS [36 and references
therein].