Pressure composition effects on superconducting A15 compounds

The phase stability of "bulk" A15 compounds prepared using ordinary metallurgical technique is contrasted with high pressure-high temperature synthesis in relation to the formation of high Tc"stoichiometric" compounds. Alloys of Nb-Ge, Nb-Al, and Nb-Ga were prepared by standard metallurgical procedures and subsequently submitted to simultaneous high pressure-high temperature treatment. These materials were characterized as to phase development and superconducting properties to evaluate the influence of the high pressure treatment. The results indicate that high Tcmaterials may ultimately be obtained by high pressure-high temperature synthesis. The high pressure phase stability of A15 compounds is discussed. The phase formation of off-stoichiometric high TcA15 compounds is also presented in terms of a non-equilibrium process involving a high quench rate.