Abstract
Neutron scattering measurements have been performed on polycrystalline samples of the newly
discovered layered superconductor LaO0:5F0:5BiS2, and its nonsuperconducting parent compound
LaOBiS2. The crystal structures and vibrational modes have been examined. Upon F-doping,
while the lattice contracts signi cantly along c and expands slightly along a, the buckling of the
BiS2 plane remains almost the same. In the inelastic measurements, a large di erence in the high
energy phonon modes was observed upon F substitution. Alternatively, the low energy modes
remain almost unchanged between non-superconducting and superconducting states either by F-
doping or by cooling through the transition temperature. Using density functional perturbation
theory we identify the phonon modes, and estimate the phonon density of states. We compare these
calculations to the current measurements and other theoretical studies of this new superconducting
material.
