Metal chalcogenides are an important class of materials consisting of metal and chalcogenides (S, Se, Te) in the form of binary, ternary, and multinary compounds. Herein, we present a cation exchange induced transformation from pyrite CuSe2 to spinel CuCr2Se4 nanocrystals. The products have been synthesized by heat-up method in which the reaction temperature plays an important role. The predominant phase formed at the temperature range of 250-300 oC was Cr- doped pyrite CuSe2. The concentration of Cr (III) increased as a function of reaction temperature and reached to 50% at 300 oC (Cu0.5Cr0.5Se2). By increasing the reaction temperature, pyrite Cu0.5Cr0.5Se2 transformed to spinel CuCr2Se4 phase. Pure spinel CuCr2Se4 has been formed at the range of 330-360 oC. The XRD patterns of the intermediate compositions formed in the range of 300-330 oC show that the relative intensity of peaks corresponding to pyrite phase gradually decreases with the reaction temperature, whereas the intensity of the spinel phase peaks increases. The point by point EDS analysis of the mentioned intermediate products revealed different Cu-, Cr-, and Se- compositions between Cu0.5Cr0.5Se2 to CuCr2Se4 exhibiting the increasing the chromium content of the pyrite phase leading to the formation of spinel phase. The superlattice of CuCr2Se4 was formed from the combination of 8 cubic pyrite unit cells of Cu0.5Cr0.5Se2 in which the octahedral position of Cr(III) ions remains constant and copper ions diffuse into the neighboring vacant tetrahedral position and Se2- ions resulting from the reduction of the dimers of Se22- diffuse into the neighboring sites which are approximately 1.38 Å away.

Mechanism of phase transformation from CuSe2 to CuCr2Se4 nanocrystals via cation exchange

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

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