The thermal decomposition temperature and the superconductivity of nine substituted systems (Y is substituted by Gd, Dy, Pr; Ba by Sr, Ca; Cu by Sn, Al, Zn, Ni, respectively) were studied systematically. The results reveal that there is a close relationship between the ${\mathit{T}}_{\mathit{c}}$ and the thermal decomposition temperature, and that the ${\mathit{T}}_{\mathit{c}}$ is always suppressed as the thermal decomposition temperature is lowered. The authors consider that the thermal stability may be one of the predominant factors for the superconductivity.

• Received 9 April 1990

DOI:https://doi.org/10.1103/PhysRevB.42.2253