  Superconductivity at 33 K in Sr2VO3FeAs is completely suppressed by small
amounts of V-doping in Sr2VO3[Fe0.93(+/-0.01)V0.07(+/-0.01)]As. The crystal
structures and exact stoichiometries are determined by combined neutron- and
x-ray powder diffraction. Sr2VO3FeAs is shown to be very sensitive to Fe/V
mixing, which interferes with or even suppresses superconductivity. This
inhomogeneity may be intrinsic and explains scattered reports regarding Tc and
reduced superconducting phase fractions in Sr2VO3FeAs. Neutron diffraction data
collected at 4 K indicates incommensurate mag- netic ordering of the
V-sublattice with a propagation vector q = (0,0,0.306). This suggests strongly
correlated vanadium, which does not contribute significantly to the Fermi
surface of Sr2VO3FeAs.
