Control of the superconducting properties of Sr2-xCaxVO3 FeAs through isovalent substitution

The effect of the isovalent substitution of Sr by Ca on the structure and superconducting properties of Sr Ca VOFeAs is described in the compositional range 0≤x≤0.5. SQUID magnetometry measurements reveal that after an initial increase in T, which is maximised at 29.5 K in SrCaVOFeAs, a rapid suppression of superconductivity is observed with increasing x. XANES spectra of Sr Ca VOFeAs collected on the Fe and V absorption K-edges show that the position of both edges are invariant with composition within the experimental uncertainty. A combination of synchrotron X-ray powder diffraction and neutron powder diffraction techniques is used to rationalise the observed changes in T with x, in terms of changes to the structure of the FeAs layer upon partial Ca substitution. These findings demonstrate that superconductivity in the Fe-based superconductors is extremely sensitive to the crystal structure with T maximised in samples with regular FeAs-tetrahedra. © 2014 Elsevier Inc. All rights reserved