The crystal structure of chalcopyrite (CuFeS₂) and AgFeS₂: The permutoidic reactions KFeS₂ → CuFeS₂ and KFeS₂ → AgFeS₂

Abstract

Abstract New evidence has been given that chalcopyrite (CuFeS 2 ) has a crystal structure according to Pauling and Brockway 3 ) and not according to Burdick and Ellis 2 ) : in a rotation diagram taken with CoK radiation of a cylindrical chalcopyrite crystal around the [001] axis weak interzones can be seen which are only compatible with the Pauling‐Brockway structure (see fig. 2). AgFeS 2 prepared by pseudomorphic transformation of KFeS 2 in a AgNO 3 solution has the same structure as chalcopyrite. The cell constants are a = b = 5.66 Å and c = 10.30 Å. The space group is also D 12 2d ‐142d with 4 molecules of AgFeS 2 per cell. The atomic positions are the same as those given for chalcopyrite by Pauling and Brockway, with a parameter value x 8 of about 1/4. The “chain” direction (i.e. the [001] direction of the KFeS 2 crystal from which the AgFeS 2 crystal was prepared) is [100]. The fact that AgFeS 2 may be considered as having originated from CuFeS 2 by isomorphic substitution is new, almost superfluous evidence that chalcopyrite has the Pauling‐Brockway structure. The artificial CuFeS 2 , prepared by pseudomorphic transformation of KFeS 2 , has a crystal structure showing great similarity to the structure of chalcopyrite, but from the X‐ray diagram it is impossible to deduce whether this similarity is also valid for the details. From the fact that AgFeS 2 is isomorphic with chalcopyrite it follows that the artificial CuFeS 2 .will probably have the same Pauling‐Brockway structure as chalcopyrite, and that here also the “chain” direction will be [100]. Finally the permutoidic reactions KFeS 2 → AgFeS 2 and KFeS 2 → CuFeS 2 are discussed.