Variation of physical properties in the nominal Sr4V2O6Fe2As2

Research highlights: → In the nominal Sr4V2O6Fe2As2, physical properties (temperature- and field-dependent magnetization, heat capacity and resistivity) vary depending on the sample purity and the synthesis conditions. → Using a combination of X-ray and neutron diffraction techniques, there are no structural transitions in Sr4V2O6Fe2As2, but there is some evidence of magnetic order. → There is a correlation between superconducting transition temperature (TC) and c-lattice parameter. TC decreases with increases in c- and sample purity. → First principles calculations show that vanadium may cross from a non-superconducting near-ferromagnetism itinerant V3+ material, with a high density-of-states, to a superconducting state based on the insulating vanadium-oxide layers. - Abstract: We show using a combination of powder X-ray and neutron diffraction, first-principles calculations, temperature- and field-dependent magnetization, heat capacity and resistivity data that the superconducting behavior of 'Sr4V2O6Fe2As2' is dependent on synthesis conditions, particularly, heating profiles result in unintentional chemical doping. This compound can be tuned from a state in which the vanadium electrons are itinerant with a high electronic density of states, to a state where the vanadium-oxide layers are insulating and presumably magnetic.