X-ray diffraction study of spontaneous strain in Fe-pnictide superconductor, NdFeAsO0.89F0.11

The lattice parameters of a Nd 1111 Fe-pnictide superconductor, NdFeAsO_0.89F_0.11, 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 (Fe_1−x Co _x )₂As₂, in addition to the previous lattice parameter measurements of YBa₂Cu₃O_6.5, MgB₂, La_1.85Sr_0.15CuO₄, and Ba_0.6K_0.4BiO₃.