Structure and temperature dependence of conductivity of $Ag_{2.5}Se-Se$ composite

Rapid solidification of $Ag$-53 at. % Se alloy resulted in the formation of a composite mixture of $Ag_{2.5}Se$ and $Se$. The microstructure consists of spherical $Se$ grains of $2–20 \mu m$ size, randomly distributed in a matrix of $Ag_{2.5}Se$. The $Se$ grains were found to be layered hexagonal while the $Ag_{2.5}Se$ had an orthorhombic crystal structure. The unit cell size of this phase, however, was twice that reported for the equilibrium orthorhombic $Ag_2Se$ compound. The conductivity sigma variation with temperature in the range 80–320 K was found to be similar to that observed in degenerate semiconductors. The sigma decreased from $295 \Omega^{-1} cm^{-1}$ at room temperature to a saturation value of $70\Omega^{-1} cm^{-1}$ for temperatures