We have investigated the vortex phase diagrams of modulation-free Bi 1.7 Pb 0.4 Sr 2 Ca 0.9 Cu 2 O 8 crystals and Pb-free Bi 2 Sr 2 CaCu 2 O 8+ δ crystals. In (Bi,Pb)-2212 crystals, the strongly reduced anisotropy as well as the presence of a significant amount of disorder induce important differences compared to Bi-2212 crystals. We have probed the activation energies of the vortices by means of magnetic relaxation measurements, both above and below the second-magnetization peak. In the vortex phase below the peak, a power law dependence U ∝ (1/ j ) μ is found, with an exponent μ = 0.54 which compares favorably with the Bragg Glass prediction. In the disordered phase situated above the second-magnetization peak line, the barriers are found to slowly diverge as U ∝ ln(1/ j ). This suggests the existence of a glassy state in this region of the phase diagram. We have carefully measured the onset of the irreversibility in the disordered phase in both crystals. Above the 2D–3D crossover field H cr , the resulting irreversibility lines are shown to be qualitatively described using a Lindemann approach in a 2D fluctuation regime.
