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

Abstract

A comparative study of the effect of donor–acceptor defect pairs [ ( In , Ga ) Cu + 2 , 2 V 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.