The irreversibility temperatures ${\mathit{T}}_{\mathit{r}}$(H) for the c-axis-oriented powders of pure and alloyed ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$,${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$${\mathrm{O}}_8$, and ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{Ca}}_2$${\mathrm{O}}_{10}$ were measured for c∥H. The results suggest that these temperatures are not the theoretically predicted vortex-lattice melting temperatures nor the vortex-glass-to-liquid transition temperatures.

• Received 15 August 1990

DOI:https://doi.org/10.1103/PhysRevB.42.8756