  Electron irradiation has been used to introduce point defects in a controlled
way in the CuO2 planes of underdoped and optimally doped YBCO. This technique
allows us to perform very accurate measurements of Tc and of the residual
resistivity in a wide range of defect contents xd down to Tc=0. The Tc decrease
does not follow the variation expected from pair breaking theories. The
evolutions of Tc and of the transition width with xd emphasize the importance
of phase fluctuations, at least for the highly damaged regime. These results
open new questions about the evolution of the defect induced Tc depression over
the phase diagram of the cuprates
