  The onset temperature of superconducting fluctuation Tonset of Bi2Sr2-xRxCuOy
(R=La and Eu) was studied by measuring the Nernst effect. We found that Tonset
has a x and R dependence that is quite different from both the pseudogap
temperature T* and the critical temperature Tc. Our results support the picture
that the incoherent superconductivity, which has been observed below Tonset, is
qualitatively different from the pseudogap phenomenon that is characterized by
T*. The experimentally obtained phase diagram indicates that the pseudogap
state suppresses Tc and enhances superconducting fluctuation while having only
small influence on Tonset.
