Reinvestigation of the zemannite structure and its dehydration behavior: a single-crystal X-ray and atomistic simulation study

Cametti, Georgia; Churakov, Sergey; Armbruster, Thomas Michael (2017). Reinvestigation of the zemannite structure and its dehydration behavior: a single-crystal X-ray and atomistic simulation study. European journal of mineralogy, 29(1), pp. 53-61. E. Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller) 10.1127/ejm/2017/0029-2587

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Single-crystal X-ray data were collected in steps of 25 °C up to 200 °C on a natural sample of zemannite, Mg0.5[ZnFe3þ(TeO3)3]·4.5H2O. Ab initio simulations were performed to determine the hydrogen-bonding network to get better insight into the mechanism of the dehydration process.
At room temperature, zemannite is hexagonal with cell parameters a = 9.4301(12) Å, c = 7.6692(10) Å, V = 590.63(13)Å3. The structure was refined in the non-centrosymmetric space group P63, instead of P63/m. Ab initio simulations suggested an ordered Fe/Zn
distribution at the octahedral sites that resulted in agreement with P63 symmetry.
The dehydration starts at 100 °C and proceeds with continuous loss of the non-Mg-bonded H2O up to 125 °C. At 150 °C, the interstitial water is lost leading to 3H2Opfu. The polyhedral framework does not undergo significant modifications. The unit-cell volume slightly decreases from 590.63(13)Å3 at room temperature to 577(2)Å3 at 200 °C.

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