Mössbauer Effect of Te125 in Simple-Cubic and Amorphous Tellurium-Base Alloys

摘要

Recoilless resonant absorption of the 35.6-KeV γ ray (3/2+ to ½+ transition) in Te125 has been observed in both simple-cubic and amorphous tellurium-base alloys obtained by rapid cooling from the liquid state. As expected from its cubic symmetry, the simple-cubic (one atom/unit cell) metastable AuTe2 gives a single-peak Mössbauer spectrum with a half-width 0.88±0.05 cm/sec and an isomeric shift of 0.03±0.01 cm/sec. The monoclinic AuTe2, which is the equilibrium form of this compound, unexpectedly shows also a single-peak spectrum with an isomeric shift 0.04±0.01 cm/sec. However, the latter is about 23% broader than the former. On the basis of the atomic arrangement of the monoclinic AuTe2, this line broadening is attributed to a weak quadrupole interaction. These findings are consistent with the fact that both polymorphs exhibit metallic conduction of the same order of magnitude. The Mössbauer spectrum of the metastable amorphous alloy Te70Cu25Au5 exhibits a well-resolved quadrupole splitting of 0.74±0.02 cm/sec, which is about the same as that of crystalline tellurium. The fact that the amorphous alloy has a quadrupole splitting of the same magnitude as that of crystalline tellurium confirms the hypothesis proposed previously that the metastable amorphous tellurium-base alloys consist of randomly oriented spiral chains of tellurium, with the atoms of the minor constituent (s) randomly distributed between the chains. As a consequence of the chain retention in the amorphous alloy, there is predominantly a covalent bonding like that in crystalline tellurium. This conclusion offers a possible explanation of the experimental fact that the amorphous alloy shows a semiconducting behavior similar to that of crystalline tellurium.