Solid solution, lattice parameter values, and effects of electronegativity in the (Cu1−xAgx)(Ga1−yIny)(Se1−z Tez)2 alloys

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Abstract
Equilibrium conditions for the alloy system (Cu1−xAgx)(Ga1−yIny) (Se1−zTez)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.