  Eu0.5La0.5FBiS2-xSex is a new BiS2-based superconductor system. In
Eu0.5La0.5FBiS2-xSex, electron carriers are doped to the BiS2 layer by the
substitution of Eu by La. Bulk superconductivity in this system is induced by
increasing the in-plane chemical pressure, which is controlled by the Se
concentration (x). In this study, we have analysed the crystal structure of
Eu0.5La0.5FBiS2-xSex using synchrotron powder diffraction and the Rietveld
refinement. The precise determination of the structural parameters and thermal
factors suggest that the emergence of bulk superconductivity in
Eu0.5La0.5FBiS2-xSex is achieved by the enhanced in-plane chemical pressure and
the decrease in in-plane disorder.
