M�ssbauer effect of119Sn in amorphous superconducting metals

Abstract

Mossbauer spectra for119Sn in crystalline and disordered Sn, as well as in crystalline and liquid-like amorphous Sn1-xCux (X=0.10−0.18), have been measured at 2.6 K≦T≦108 K. The Debye-Waller-Factor (DWF) obtained from the spectra is identical for the crystalline and for the disordered phase. The DWF of the amorphous phase is smaller than the DWF of the crystalline phase athigh temperatures, but it shows a stronger temperature dependence than the DWF of the crystalline phase and reaches the latter one at about 4 K. From this low-temperature result we conclude that the differences of the Eliashberg functionα2(ω)F(ω) and of the superconducting transition temperatureTc in these two phases cannot be related to changes in the phonon spectrumF(ω), but must result from changes of the interaction parameterα2 (ω). A comparison between DWF,α2F, and specific heat data is performed. From the values for the isomeric shift of the Mossbauer line we can show that the hybridisation and covalency of the electronic bonds present in the crystalline and in the disordered phases are destroyed in the amorphous phase. Both, the DWF and the isomer shift demonstrate that the electronic properties of crystalline and amorphous Sn(Cu) differ appreciably. The electronic and superconducting properties of amorphous Sn(Cu) are similar to the properties of the high pressure phase of tin.