Synthesis and stability of single-phase chalcopyrite - a potential reference material for key investigations in chemistry and metallurgical engineering.

Single-phase chalcopyrite (CuFeS) is a key reference material in the development of new metallurgical processes to ensure a reliable copper supply. Here, we report on the successful synthesis of single-phase chalcopyrite and its phase behaviour. We further rationalise different opinions previously expressed in the literature. Chalcopyrite synthesis has been studied at 450 °C with varying sulfur contents and analysed using X-ray powder diffraction (XRPD) and Fe-Mössbauer spectroscopy. With stoichiometric amounts (Cu : Fe : S = 25 : 25 : 50) the main chalcopyrite phase is contaminated with pyrite (FeS) and bornite (CuFeS). Single-phase chalcopyrite was only found in samples containing around 49.7 at% sulfur in the reactant mixture. Mößbauer spectroscopy confirmed that chalcopyrite contains trivalent iron. Temperature dependent XRPD measurements detected an order-disorder phase transition starting at 485 °C. At temperatures above 535 °C, samples only contained intermediate solid solutions. These adopt the sphalerite structure with the lattice constant slightly varying with Cu : Fe ratio.