Phase formation and evolution of Cu:Zn partials in binary metal pyrophosphates Cu_(2−x)Zn_(x)P₂O₇; x ≈ 1

Highlights: • The solid solution formation of binary CuZnP₂O₇ pyrophosphate was firstly reported. • Decreasing percentage of 3CuO–2P₂O₅0.3NH₃0.2H₂O intermediates was related directly to an increasing final product. • The complete solid solution of CuZnP₂O₇ and the local geometric structure was firstly confirmed by EXAFS spectra. - Abstract: Binary metal pyrophosphate powders were prepared by the solid state reaction method and subsequently calcined at 400, 500, 600, 700, and 800 °C in order to study Cu:Zn partial evolution to the final CuZnP₂O₇ product. Synchrotron X-ray absorption, X-ray diffraction, Raman, FT-IR spectroscopy, and thermogravimetric analysis were used in this investigation. Phase evolution of the reaction products was investigated systemically. The results showed that complicated mixtures contributed to the reaction of synthesis temperature. The reaction comprised 3CuO·2P₂O₅·0.3NH₃·0.2H₂O, Cu₂P₂O₇, Zn₂P₂O₇, and Zn₂P₂O₇·3H₂O intermediates. Decreasing percentage of 3CuO·2P₂O₅·0.3NH₃·0.2H₂O intermediates was related directly to an increasing final product. Cu:Zn contents changed in Cu_(2−x)Zn_(x)P₂O₇ in the temperature range of 400–600 °C, when x ≈ 1 clearly was related linearly to the reaction temperature. The final product was confirmed by EXAFS fitting spectra as solid solution between the Cu and Zn atom in the CuZnP₂O₇ structure, and it indicated environment around metal atoms