Hydrogen and deuterium diffusion in non-stoichiometric spinel
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High pressure/temperature annealing experiments are used to determine diffusivities of H+ and D+ in non-stoichiometric spinel, a low-pressure analogue for nominally anhydrous minerals in Earth’s mantle. Data are fitted to the following Arrhenius law: Diffusivity (m2/s) = 4 ± 1 × 10−12 exp(−54 ± 2 kJ mol−1/RT). At low temperatures, H+ and D+ diffusion in non-stoichiometric spinel is charge balanced by flux of O vacancies, with infrared data consistent with protonation of both octahedral and tetrahedral O–O edges in non-stoichiometric spinel, and additional fine structure due to Mg–Al mixing and/or coupling of structurally incorporated H+ with cation vacancies. Absence of changes in the fine structure of O–H absorption bands indicates that H+ can become locally coupled and uncoupled to other defects during bulk diffusion. As such, proton conductivity in spinel group minerals, arising from faster flux of uncoupled H+, can only be calculated from H+ mobility data if the extent of defect coupling is constrained.
Bromiley , G D , Brooke , J & Kohn , S C 2017 , ' Hydrogen and deuterium diffusion in non-stoichiometric spinel ' , High Pressure Research , vol. 37 , no. 3 , pp. 360-376 . https://doi.org/10.1080/08957959.2017.1353091
High Pressure Research
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