X-ray diffraction study of spontaneous strain in superconducting

The lattice parameter of Ba 0.6 K 0.4 BiO 3 , which is a well-studied conventional superconductor, was measured by the X-ray Rietveld method between 10 K and room temperature. A very small change in the lattice parameter could be detected in the superconducting phase. The change could be attributed to a spontaneous strain generated in the superconducting phase by the coupling between a superconducting order parameter and the strain. Previously published data on Y Ba 2 Cu 3 O 6.5 and MgB 2 were analyzed, and the present results were compared with our previously obtained results on La 1.85 Sr 0.15 CuO 4 . It was concluded that this coupling phenomenon is common to all superconductors.