Synthesis and stability of Nb3Ge made by electron-beam codeposition

Niobium-germanium (Nb-Ge) films which remain superconducting up to about 22.5 °K have been prepared using high-rate (33–133 Å/sec) electron-beam codeposition. The presence of oxygen in the deposition chamber is necessary for stabilizing the high-Tc A15 phase. Analysis of Nb-Ge films shows that oxygen extends, with some temperature dependence, the Ge-rich range of the A15 phase with an accompanying decrease in the lattice constant. An amorphous component in the films is first detected below a deposition temperature of 800 °C. It increases rapidly at lower temperatures and becomes dominant at about 600 °C. The A15 phase diagram was determined for the first time for temperatures below 875 °C.