  Temperature dependence of longitudinal optical phonons with oxygen character
was measured in La1-xSrxMnO3 (x=0.2, 0.3) by inelastic neutron scattering in
the (1 0 0) cubic direction. The zone center mode intensity is consistent with
the Debye-Waller factor. However the intensity of the bond-stretching phonons
half way to the zone boundary and near the zone boundary decreases dramatically
as the temperature increases through the ferromagnetic (FM) transition. We
found evidence that the lost phonon spectral weight might shift into polaron
scattering at the same wavevectors. The temperature evolution starts well below
the onset of the FM transition suggesting that the transition is driven by
phonon renormalization rather than by magnetic fluctuations.
