Tutton K 2 Zn(SO 4 ) 2 (H 2 O) 6 salt: Structural-vibrational properties as a function of temperature and ab initio calculations.

In this work, a thorough study of Tutton K ₂ Zn(SO ₄ ) ₂ (H ₂ O) ₆ crystal was performed. Structural, electronic, vibrational, and thermal properties were analyzed and discussed. Calculations based on the density functional theory (DFT) were performed to provide a correct assignment of vibration modes (90 active Raman and 93 active IR), and analyses of band structure and density of states. Powder X-ray diffraction (PXRD) at 300 K showed that the Tutton crystallizes in monoclinic symmetry with space group P2 ₁ /a. An electronic bandgap of 4.66 eV, typical of insulating material, was estimated by band structure calculation. The thermal analysis in the 300-700 K range by coupled TG-DTA thermogram revealed two endothermal events and one exothermal. Such events were investigated by PXRD and Raman spectroscopy as a function of temperature, where three phase changes associated with dehydration and crystallization were observed. The new phase structures were determined by the Le Bail and Rietveld methods. The thermal-structural findings suggest that the K ₂ Zn(SO ₄ ) ₂ (H ₂ O) ₆ Tutton can be considered a promising thermochemical compound for residential heat storage devices due to a low onset for the dehydration temperature (≈327 K) and a high enthalpy of dehydration (77.4 kJ/ mol H ₂ O).
Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
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