Superconducting properties of amorphous Zr-Ge binary alloys

A new type of refractory metal-metalloid amorphous alloys exhibiting superconductivity has been found in a binary Zr-Ge system by a modified melt-spinning technique. Specimens are in the form of continuous ribbons 1 to 2 mm wide and 0.02 to 0.03 mm thick. The germanium content in the amorphous alloys is limited to the range of 13 to 21 at%. These amorphous alloys are so ductile that no cracks are observed even after closely contacted bending test. The Vickers hardness and crystallization temperature increase from 435 to 530 DPN and from 628 to 707 K, respectively, with germanium content, and the tensile fracture strength is about 1460 MPa. Furthermore, the amorphous alloys exhibit a superconducting transition which occurs very sharply. The superconducting transition temperature (T_c) increases with decreasing germanium content and reaches a maximum value of 2.88 K for Zr₈₇Ge₁₃. The upper critical magnetic field for Zr₈₇Ge₁₃ alloy was of the order of 21.8 kOe at 2.0 K and the critical current density for Zr₈₅Ge₁₅ alloy was about 175 A cm^–2 at 1.70 K in the absence of an applied field. The upper critical field gradient atT_c and the electrical resistivity at 4.2 K increase significantly from 24.6 to 31.5 kOe K^–1 and from 235 to 310cm, respectively, with the amount of germanium. The Ginzburg-Landau (GL) parameter and the GL coherence length §_GL (0) were estimated to be 72 to 111 and about 7.9 nm, respectively, from these experimental values by using the Ginzburg-Landau-Abrikosov-Gorkov (GLAG) theory and hence it is concluded that the Zr-Ge amorphous alloys are extremely soft type-II superconductor with high degree of dirtiness which possesses theT_c values higher than zirconium metal, in addition to high strength combined with good ductility.