Publisher： John Wiley & Sons Inc
E-ISSN： 2156-2202|99|B9|17717-17727
ISSN： 0148-0227
Source： Journal Of Geophysical Research, Vol.99, Iss.B9, 1994-09, pp. : 17717-17727
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Abstract
High‐pressure infrared (IR) spectra of most lattice modes and of hydrous impurities of Fe‐bearing wadsleyite were measured from O to 23 GPa. At ambient conditions, 29 of the 35 expected IR bands were revealed through a combination of reflection and absorption measurements. Absorption spectra of a magnesium end‐member at ambient conditions were similar. The pressure dependence of eight OH vibrations were established to 12 GPa. The degree of hydrogen bonding is inferred from the values of the hydroxyl frequencies and their response to pressure: Five hydroxyls with low v have negative ∂v/∂P and thus moderate to strong hydrogen bonding, whereas three OH groups with high v have near‐zero or positive values of ∂v/∂P and thus weak or no hydrogen bonding. This information, the response of the OH bands to Fe/Mg exchange, and X ray data were used to assign the most intense OH bands to the structural sites, O(1) and O(2). These assignments of hydroxyl vibrations are consistent with previous theoretical models. Our study of high‐pressure OH vibrations in nominally anhydrous wadsleyite indicates that hydrogen impurities in wadsleyite are stable during compression. Our data are consistent with the previously observed minor structural change at around 9 GPa which is possibly due to a slight change in the compression mechanism.
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