Mössbauer Effect ofTe125in Simple-Cubic and Amorphous Tellurium-Base Alloys

Abstract

Recoilless resonant absorption of the 35.6-KeV $\gamma$ ray (${\frac{3}{2}}^{+}$ to ${\mathrm{½}}^{+}$ transition) in ${\mathrm{Te}}^{125}$ 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 Au${\mathrm{Te}}_2$ 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 Au${\mathrm{Te}}_2$, 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 Au${\mathrm{Te}}_2$, 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 ${\mathrm{Te}}_{70}$ ${\mathrm{Cu}}_{25}$ ${\mathrm{Au}}_5$ 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.