N.M.R. study of changes in bonding and the metal-non-metal transition in liquid caesium-antimony alloys

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Abstract
133Cs N.M.R. results for the resonance shift and nuclear relaxation rate in liquid Cs-Sb alloys are presented for the concentration range 0≤x Sb≤0·62. On the Cs-rich side of the compound composition Cs3Sb, the correlation between Knight shift and magnetic susceptibility or electrical conductivity strongly indicates that a pseudogap forms in this liquid as the metal-non-metal transition is approached. Before the onset of the non-metallic state near x Sb = 024 the electron correlation time τ reaches a value of 4 × 10−14 s. At the composition Cs3Sb, both the shift and the relaxation rate are very sensitive to small deviations from stoichiometry; the minimum observed value of the shift is 0·16%, that of the relaxation rate T −1 1 is 2 × 103 s−1. The behaviour close to stoichiometry is not inconsistent with non-degenerate localized states within the gap. On the Sb-rich side of Cs3-Sb only a small variation in shift is found and T −1 1 decreases to 500 s−1 at the compound composition CsSb. In this concentration range a strong reduction in the s-electron density at the Cs nucleus is inferred from the change in the hyperfine field. This result and, in particular, the long correlation time τ = 10−12 s near CsSb, together with the estimated quadrupolar correlation time > 10−11 s show that long-lived molecular groups, probably with partial covalent bonding character, are probably present in non-metallic liquid Cs-Sb alloys.