Melting-induced electron localization: (133)Cs NMR study of solid and liquid CsAu.

We describe (133)Cs NMR study of the ionic intermetallic semiconductor CsAu and the transition to its salt-like liquid state. Measurements of the resonance shift and nuclear relaxation rates extend from room temperature- dependent spin-lattice relaxation rate and accompanying shift in the solid are attributed to extrinsic, nondegenerate, delocalized electrons which are excited from a donor band about 0.25 eV below the conduction band. A sharp 25-fold increase in the relaxation rate at the melting point is not accompanied by a similar jump in the shift showing that the conduction electrons become localized immediately on passing to the liquid state.