Electrical resistivities of liquid Na-Bi and Rb-Bi alloys

The electrical resistivities p of liquid Na-Bi and Rb-Bi alloys have been measured as functions of composition and temperature. Plotted as a function of composition the resistivity of Na-Bi exhibits a maximum at the composition corresponding to Na 3 Bi while for Rb-Bi two maxima, at 25 and 40 at.% Bi, can be discerned. In both alloys, the maximum value of rho is far beyond the metallic range. In the composition ranges around the maxima the temperature dependence d rho /dT of the resistivity is negative and -d rho /dT attains extraordinarily large values. The results can be explained by assuming that for Na-Bi a strong octet compound is formed whereas for Rb-Bi both an octet and a clustered compound are formed. Comparison with the other alkali-Bi alloys shows that in the sequence from Li-Bi to Cs-Bi a transition from a simple octet configuration to a clustered configuration occurs.