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.