Local order in liquid and amorphous Cs-Sb.

Abstract

We have investigated the effects of local order on the density of states and the conductivity of liquid and amorphous Cs-Sb alloys as a function of concentration. By using a numerical Monte Carlo technique that treats the local atomic environment correctly, we show that the very sharp minimum in the conductivity that has been reported in the liquid near the ${\mathrm{Cs}}_{3}$Sb stoichiometry can be explained by a local-order-induced gap in the density of states if a very high degree of local order is assumed. Although we find a substantial degree of charge transfer, \ensuremath{\sim}0.6 electron/Cs atom, this charge transfer is far from complete, in agreement with the analyses of a variety of other types of experimental results. In the concentration region 30--50 at. % Sb, we find that the presence of ${\mathrm{Sb}}^{\mathrm{\ensuremath{-}}}$-${\mathrm{Sb}}^{\mathrm{\ensuremath{-}}}$ covalent bonds, indicated by neutron-diffraction measurements, can accurately account for the measured conductivity which varies from \ensuremath{\sim}50 to \ensuremath{\sim}100 (\ensuremath{\Omega} cm${)}^{\mathrm{\ensuremath{-}}1}$. The strong temperature dependence of the conductivity in this concentration region can then be understood in terms of the dissociation of these bonds. By also applying our model to amorphous Cs-Sb, we explain the differences between the measured conductivities of the liquid and amorphous alloys.