  We present measurements of the thermal expansion coefficient alpha of
polycrystalline LaFeAsO1-xFx (x <= 0.1). The magnetic and structural
transitions of the samples with x <= 0.04 give rise to large anomalies in
alpha(T), while the onset of superconductivity in the crystals with x >= 0.05
is not resolved. Above the structural transition, the thermal expansion
coefficient of LaFeAsO is significantly enhanced. This is attributed to
fluctuations, which also affect the electrical transport properties of the
compound. The complete absence of these fluctuations in the superconducting
samples even for x = 0.05 is taken as evidence for an abrupt first-order type
of suppression of the structural and magnetic transitions upon F doping.
