X-ray Diffraction Study of Spontaneous Strain in Fe-Pnictide Superconductor, NdFeAsO0.89F0.11

The lattice parameters of a Nd 1111 Fe-pnictide superconductor, NdFeAsO0.89F0.11, were accurately measured using X-ray diffraction between 20 K and 280 K. A very small change in the lattice parameter could be detected in the superconducting phase. This change can be attributed to a spontaneous strain generated in the superconducting phase by the coupling between a superconducting order parameter and the strain. The present results are compared with the thermal expansion coefficients of Ba (Fe1−x Co x )2As2, in addition to the previous lattice parameter measurements of YBa2Cu3O6.5, MgB2, La1.85Sr0.15CuO4, and Ba0.6K0.4BiO3.