Synthesis and stability of Nb3Ge made by electron-beam codeposition

Abstract

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‐T_c 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.