X-ray diffraction study of spontaneous strain in the iron-based superconductor Sr4V2Fe2As2O6−δ6−δ

•X-ray diffraction of iron-based superconductor Sr4V2Fe2As2O6.•Detection of anomalous changes in lattice parameter at magnetic and superconducting transitions.•These anomalies are spontaneous strain caused by coupling between starin and order parameter.

The lattice parameters of the iron-based superconductor Sr4V2Fe2As2O6−δ6−δwere measured by the X-ray diffraction method between 10 K and 270 K. Anomalous changes in the lattice parameter c could be clearly detected at the magnetic phase transition and the superconducting transition. Based on the Landau theory of phase transition, these anomalies can be attributed to a spontaneous strain caused by the coupling between the strain and an order parameter. The signs of the uniaxial pressure derivative along the c axis of the transition temperatures are estimated using the Ehrenfest relation.