Augmented chalcopyrites: A search for new Cu-In-Te phases

Chalcopyrites are ternary crystalline compounds which have found use in a diverse array of applications, from solar cells to thermoelectric devices. These are known to be ternary-compound analogs to diamond or sphalerite. ``Defect chalcopyrites,'' which are chalcopyrite structures stabilized with ordered vacancies and substitutions, are well attested and can serve as a method of tuning material properties through control of stoichiometry. In particular, defect chalcopyrites related to the thermoelectric compound ${\mathrm{CuInTe}}_{2}$ comprise a large range of compositions in the pseudobinary system ${({\mathrm{Cu}}_{2}\mathrm{Te})}_{x}{({\mathrm{In}}_{2}{\mathrm{Te}}_{3})}_{1\ensuremath{-}x}$, where $x<0.5$. In contrast, the converse case of ``augmented chalcopyrites,'' namely, $x>0.5$, is much less known or studied. We report the discovery of a range of ${\mathrm{Cu}}_{2}\mathrm{Te}$-rich compositions in this binary system where stable phases can potentially be found. Here, the stoichometry of augmented chalcopyrites is likely to be modulated by the concentration of defect clusters ${[{\mathrm{Cu}}_{\text{In}}^{2\ensuremath{-}}\ifmmode\cdot\else\textperiodcentered\fi{}2{\mathrm{Cu}}_{i}^{+}]}^{0}$ in chalcopyrite ${\mathrm{CuInTe}}_{2}$.