  The phase diagram of electron-doped pnictides is studied varying the
temperature, electronic density, and isotropic quenched disorder strength by
means of computational techniques applied to a three-orbital ($xz$, $yz$, $xy$)
spin-fermion model with lattice degrees of freedom. In experiments, chemical
doping introduces disorder but in theoretical studies the relationship between
electronic doping and the randomly located dopants, with their associated
quenched disorder, is difficult to address. In this publication, the use of
computational techniques allows us to study independently the effects of
electronic doping, regulated by a global chemical potential, and impurity
disorder at randomly selected sites. Surprisingly, our Monte Carlo simulations
reveal that the fast reduction with doping of the N\'eel $T_N$ and the
structural $T_S$ transition temperatures, and the concomitant stabilization of
a robust nematic state, is primarily controlled by the magnetic dilution
associated with the in-plane isotropic disorder introduced by Fe substitution.
In the doping range studied, changes in the Fermi Surface produced by electron
doping affect only slightly both critical temperatures.
