  The effects of aliovalent rare earth substitution on the physical properties
of Sr0.3Ca0.7Fe2As2 solid solutions are explored. Electrical transport,
magnetic susceptibility and structural characterization data as a function of
La substitution into (Sr_1-y_Ca_y)_1-x_La_x_Fe2As2 single crystals confirm the
ability to suppress the antiferromagnetic ordering temperature from 200 K in
the undoped compound down to 100 K approaching the solubility limit of La.
Despite up to ~30% La substitution, the persistence of magnetic order and lack
of any signature of superconductivity above 10 K present a contrasting phase
diagram to that of Ca1-xLaxFe2As2, indicating that the suppression of magnetic
order is necessary to induce the high-temperature superconducting phase
observed in Ca1-xLaxFe2As2.
