Original paper
Reinvestigation of the zemannite structure and its dehydration behavior: a single-crystal X-ray and atomistic simulation study
Cametti, Georgia; Churakov, Sergey; Armbruster, Thomas
European Journal of Mineralogy Volume 29 Number 1 (2017), p. 53 - 61
published: Mar 24, 2017
Abstract
Single-crystal X-ray data were collected in steps of 25°C up to 200° C on a natural sample of zemannite, Mg0.5 [ZnFe3+ (TeO3)3 ]· 4.5H2 O. 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 P 63, instead of P 63/m. Ab initio simulations suggested an ordered Fe/Zn distribution at the octahedral sites that resulted in agreement with P 63 symmetry. The dehydration starts at 100°C and proceeds with continuous loss of the non-Mg-bonded H2 O up to 125°C. At 150°C, the interstitial water is lost leading to 3H2O pfu. 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.
Keywords
x-ray diffraction • dehydration • md simulations • zemannite • thermal stability