Mössbauer and transport studies of amorphous and icosahedral Zr-Ni-Cu-Ag-Al alloys

Abstract

The alloy Zr65Al7.5Ni10Cu7.3Fe0.2Ag10 in the amorphous and icosahedral states,and the bulk amorphous alloy Zr65Al7.5Ni10Cu7.5Ag10, have been studied with 57FeMössbauer spectroscopy, electrical resistance and magnetoresistance techniques. Theaverage quadrupole splitting in both alloys decreases with temperature as T3/2. Theaverage quadrupole splitting in the icosahedral alloy is the largest ever reportedfor a metallic system. The lattice vibrations of the Fe atoms in the amorphousand icosahedral alloys are well described by a simple Debye model, with thecharacteristic Mössbauer temperatures of 379(29) and 439(28) K, respectively.Amorphous alloys Zr65Al7.5Ni10Cu7.5Ag10 and Zr65Al7.5Ni10Cu7.3Fe0.2Ag10have been found to be superconducting with the transition temperature,Tc, of about 1.7 K. Themagnitude of Tc and thecritical field slope at Tcare in agreement with previous work on Zr-based amorphous superconductors,while the low-temperature normal state resistivity is larger than typicalresults for binary and ternary Zr-based alloys. The resistivity of icosahedralZr65Al7.5Ni10Cu7.3Fe0.2Ag10 is larger than that for the amorphous ribbon ofthe same composition, as inferred both from direct measurements onthe ribbons and from the observed magnetoresistance. However theicosahedral sample is non-superconducting in the measurement rangedown to 1.5 K. The results for the resistivity and the superconductingTcboth suggest a stronger electronic disorder in the icosahedral phase than in theamorphous phase.