Protons and deuterons in stoichiometric and nonstoichiometric MgAl₂O₄

Abstract

The OH~ and OD^ vibrational frequencies in stoichiometric and nonstoichiometric MgAl2O4 were measured. The nonstoichiometric material had a Al/Mg ratio of 7. The diffusion coefficient of deuterons in the nonstoichiometric material at 1600 K is about 6 + 3 X 10~8 cmVs. Deuterons can readily be swept out by applying an electric field at temperatures above 1000 K.

Diffusion of proton in alumina-rich nonstoichiometric magnesium aluminate spinel

“…Incorporation of hydrogen for alumina-rich nonstoichiometric magnesium aluminate spinel was confirmed in the literature [1,2]. The solubility of hydrogen increases with the increase in the excess content of alumina [3,4].…”

Hydrogen and deuterium diffusion in non-stoichiometric spinel

“…, with protonation coupled with T site vacancies (V T ). However, both Gonzalez et al [16] and Bromiley et al [10] noted additional fine structure in O-H absorption in non-stoichiometric spinel, and a splitting of OH band 2 into at least two Gaussian contributions. Fukatsu et al [14] suggested that O-H and corresponding O-D stretching frequencies in IR spectra were consistent with protonation of both octahedral and tetrahedral edges.…”

“…In particular, non-stoichiometric spinel contains high concentrations of M site vacancies, so additionally, protonation of vacancies would appear to be highly favourable due to the strong net negative charge associated with cation vacancies (i.e. associated H i -V /// Al defects involving single or multiple protons) [10,[14][15][16]. However, in all IR spectra here relative areas of all O-H contributions remain unchanged across diffusion profiles, during either H + loss or H + gain.…”

“…hydroxyl) in the deep Earth [3,[11][12][13]. In addition to the insight which it provides on H + incorporation in major mantle NAMs, non-stoichiometric spinel has several potential technological applications, most notably as a proton conductor and H + sensor, and has been the subject of numerous investigations of electrochemical properties [14][15][16]. Spinel sensu stricto and ringwoodite are both minerals within the spinel mineral class.…”

“…Assessing H mobility in NAMs is essential in constraining the importance of H + incorporation on mantle properties and processes within the deep Earth, and in providing additional insight into H + incorporation mechanisms, for example [18][19][20][21]. H + mobility in non-stoichiometric spinel has been investigated by Canova et al [22], Fukatsu et al [14] and Gonzalez et al [16], although these studies provide only limited insight into the relative mobility of different H + defects. Furthermore, these studies were performed by annealing non-stoichiometric spinel in H-rich atmospheres at ambient pressure, and not at the high P-T conditions under which it can incorporate quantities of H + comparable to other mantle NAMs.…”