@article{fdi:010061314,
  title = {{I}nfrared signatures of {OH}-defects in wadsleyite : a first-principles study},
  author = {{B}lanchard, {M}. and {R}oberge, {M}. and {B}alan, {E}tienne and {F}iquet, {G}. and {B}ureau, {H}.},
  editor = {},
  language = {{ENG}},
  abstract = {{T}he structure and the polarized infrared absorption spectrum of {OH}-defects in wadsleyite (beta-{M}g2{S}i{O}4) are studied, at 0 and 15 {GP}a, by first-principles calculations based on density functional theory ({DFT}). {F}our types of {OH}-defects are considered: fully protonated magnesium vacancies, fully protonated silicon vacancies, silicon vacancies compensated by a magnesium cation and two protons, and {OH}-defects associated with the migration of a silicon cation to a normally vacant site, as reported by {K}udoh and {I}noue (1999). {T}he results suggest that the main absorption band constituted by a doublet (3326 and 3360 cm(-1)) corresponds to at least two types of {OH}-defects involving {M}3 vacancies with protonation of the {O}1-type {O} atoms along the {O}1 center dot center dot center dot {O}-4 edges. {T}he main contribution of the less intense band at 3581 cm(-1) is likely related to the partial protonation of a silicon vacancy (protonation of the {O}3-type oxygen) associated with the migration of the silicon cation to the {S}i2 site. {T}his assignment is consistent with several experimental constraints: wavenumber and pleochroism of infrared {OH}-stretching bands, pressure-dependence of the band wavenumber, evidence from {X}-ray diffraction of magnesium vacancies in {M}3 site, and increase of the b/a axial ratio with water content. {T}he integrated absorption coefficients of the corresponding {OH}-defects are also calculated and thus complement the set of data obtained previously for forsterite and ringwoodite. {A}bsorption coefficients of wadsleyite computed at 0 and 15 {GP}a indicate that for a precise quantification of the hydrogen content in in situ experiments, one must consider higher absorption coefficients than those determined at 0 {GP}a after quench. {I}t is also shown that a single theoretical relation can account for the three {M}g2{S}i{O}4 polymorphs at 0 {GP}a: {K}-int = 278.7 +/- 18.1 (3810 +/- 465 - x), where {K}-int is the integrated molar absorption coefficient of the {OH} stretching modes and x is the average wavenumber in cm(-1). {A}bsorption coefficients are significantly lower than the general calibrations, the use of which would lead to an underestimation of the water concentrations.},
  keywords = {{W}adsleyite ; {OH}-defect ; {IR} spectroscopy ; ab initio calculations ; {DFT}},
  booktitle = {},
  journal = {{A}merican {M}ineralogist},
  volume = {98},
  numero = {11-12},
  pages = {2132--2143},
  ISSN = {0003-004{X}},
  year = {2013},
  DOI = {10.2138/am.2013.4468},
  URL = {https://www.documentation.ird.fr/hor/fdi:010061314},
}