Optical and electrical transport measurements on amorphous mixtures of Cs and Sb

Abstract

Optical and electrical transport properties were investigated in amorphous Cs-Sb mixtures at 6 K. A metal-nonmetal transition is observed as a function of Cs atomic fraction ($X$) and both the transport and optical properties indicate that this occurs at $X=0.68$. The dc conductivity at this composition is \ensuremath{\sim} 150 ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ which is consistent with acceptable values of Mott's minimum metallic conductivity. The mixtures can be partitioned into three distinct composition regions: (1) $Xl0.64$, in which the mixtures are semiconducting; (2) $0.64lXl0.68$, in which the states near the Fermi energy apparently are localized; and (3) $Xg0.68$, in which the mixtures are metallic. The optical data indicate that within the broad composition range $0.7lXl0.95$, approximately 1.6 electrons are removed from the metallic conduction band for each Sb atom added to the system. Electrical transport data in Cs-Sb liquid alloys are compared with the present data in the amorphous solid state.