Abstract
The present study deals with chemical reactions and enthalpies during the synthesis of Cu2ZnSnSe4 (CZTSe) from CuSe, SnSe, and ZnSe in molten NaI as flux material in closed degassed ampoules. Differential thermal analysis (DTA) at heating rates 5 °C min−1 and cooling rates 10 °C min−1 were used for the determination of temperatures of phase transitions and/or chemical reactions. XRD and Raman analyses confirmed that the formation of CZTSe starts already at 380 °C after the melting of Se that deliberates from the transformation of CuSe to Cu1.8Se, and the CZTSe formation process impedes to a great extent due to the presence of solid NaI. After the melting of NaI, the formation of CZTSe is completed. For the determination of enthalpy values, the calibration with pure NaI was performed. The thermal effects and enthalpies were compared with the available known thermodynamical values. The specific enthalpy of exothermic Cu2ZnSnSe4 formation at 661 °C in NaI −36 ± 3 kJ mol−1 was determined experimentally for the first time. Ternary compound Na2SnSe3 was formed during the synthesis process. NaI·2H2O, if present in NaI, was found to be a critical issue in the synthesis process of CZTSe monograin powders in molten NaI—it gave rise to the formation of oxygen-containing by-products Na2SeO4 and Na2Cu(OH)4. The complete dehydration of NaI·2H2O at T ≤ 70 °C in vacuum is necessary to avoid the formation of oxygen-containing compounds.
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Acknowledgements
The Doctoral Studies and Internationalization Program DoRa of the European Social Funds supported this research; Estonian Science Foundation grants 9425, 8964, G8964, projects TK117T, National R&D programs AR10128 and AR12128, the Estonian Ministry of Education and Research Contract No. SF0140099s08, and the EAS project EU29713. Support in the sample preparation process by Sergei Bereznev is gratefully acknowledged.
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Leinemann, I., Zhang, W., Kaljuvee, T. et al. Cu2ZnSnSe4 formation and reaction enthalpies in molten NaI starting from binary chalcogenides. J Therm Anal Calorim 118, 1313–1321 (2014). https://doi.org/10.1007/s10973-014-4102-y
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DOI: https://doi.org/10.1007/s10973-014-4102-y