Solid solution, lattice parameter values, and effects of electronegativity in the (Cu1-xAgx)(Ga1-yIny)(Se 1-z Tez)2 alloys

Abstract

Equilibrium conditions for the alloy system (Cu1-xAg x)(Ga1-yIny) (Se1-zTe z)2 were determined throughout the complete range of composition. Polycrystalline samples of 125 different compositions, i.e., with x, y, and z=0, 0.25, 0.5, 0.75, and 1.0, were prepared by a melt and anneal technique. Different annealing temperatures in the range 600-800 °C were used depending upon the alloy composition and annealing times of up to 5 months used to attain equilibrium conditions. Debye-Scherrer x-ray powder photographs were used to investigate the equilibrium conditions. It was found that single phase chalcopyrite structure was obtained for all compositions of the copper (x=0), indium ( y=1), and tellurium (z=1) sections but that miscibility gaps occurred in the silver (x=1), gallium ( y=0), and selenium (z=0) sections, and that these miscibility gaps extended through the general alloy system. Values of lattice parameters a and c were determined for all samples showing single phase condition and for each of the above sections the variations of a and c with composition were fitted to power series in the appropriate composition coordinates. Hence contours of constant a and constant c were determined. From the parameters for each section, general series expressions in x, y, and z were developed and the values from these compared with the experimental data for the general alloys. It is shown that a modified Weaire and Noolandi relation of the form [2-(c/a)] =K(XI-XIII+qXVI)2 fits all of the experimental data. Averaged values of K and q were obtained by fitting separately to different sections of the alloy system and also to all alloys of the complete system.