Effect of donor-acceptor defect pairs on the crystal structure of In and Ga rich ternary compounds of Cu-In(Ga)-Se(Te) systems

A comparative study of the effect of donor-acceptor defect pairs [(In, Ga)(Cu)(+2),2V(Cu)(-1)] on the unit cell parameters a, c and V of the ordered defect compounds that are intermediate phases of the pseudo-binary [Cu-2(Se,Te)](1-x) [(In-2,Ga-2)(Se-3,Te-3)](x) system has been carried out. It is found that a, c and V decrease linearly with the increase in the fraction of cation vacancies to the total number of cation positions, m, or the fraction of the interacting donor-acceptor defect l per unit, respectively, in the chemical formula. The reduction in the unit cell dimensions is explained as due to the decrease in the effective cation radius r(eff) caused by the increase in m or l or decrease in n. The linear dependence of r(eff) on a, c, and V has important consequences. This behavior can be used to predict the unit cell parameters of other ODCs that may have chalcopyrite-related structure and have not been reported so far. (c) 2005 Elsevier Ltd. All rights reserved.