Title: Hydrogen%20bonding%20in%20minerals%20under%20pressure
1- Hydrogen bonding in minerals under pressure
- Bjoern Winkler
- Goethe University Frankfurt a. M.
- b.winkler_at_kristall.uni-frankfurt.de
2Contents
- Motivation
- Methods
- diffraction
- spectroscopy
- modelling
- Examples
- diaspore
- the hydrogarnet substitution
- nominally anhydrous minerals wadsleyite
3Motivation
- Hydrogen bonding plays an important role in a
very large number of processes - Numerous aspects are studied
- structure and dynamics of hydrogen bonds in
hydrous phases - incorporation of hydrogen (water) into
nominally anhydrous phases - where are the hydrogen atoms ?
- how much water can be incorporated ?
- effects of anharmonicity
- Test for theories
4The Hydrogen Bond
5Applicability of diffraction techniques
- single crystal x-ray in DAC
- large P range but hydrogens difficult to
localize - single crystal neutron in DAC
- moderate P - neutron Laue diffraction
(feasibility study worked on VIVALDI_at_ILL)
x-ray powder diffraction at P ? neutron powder
diffraction deuteration necessary, limited P-
range
6IR spectroscopic characterisation
- n(OH) 2700 - 3600 cm-1
- powder and single crystal IR spectroscopy as
well-established tools, but quantitative
measurements require calibration - correlations between n(OH) and d(O...O), d(O-H),
d(H...O) at ambient pressure well established
(Libowitsky (1999) and references therein)
7Modelling of hydrogen bonded systems
Force field (empirical potential) models dont
work too well for hydrous silicates and related
materials
- Parameter-free approach
- modeling of crystals periodic boundary
conditions - density functional theory (DFT)
- athermal limit, Born-Oppenheimer Approximation
- lattice dynamics from DFPT or finite displacement
approach - plane waves pseudopotentials or LCAO basis set
8- Example I diaspore, a-AlOOH
9Diaspore, a-AlOOH
Pbnm, Z 4 a 4.401(1) Å b 9.421 (4) Å c
2.845(1) ŠV 117.68 (8) ų intermediate
H-bond relatively high symmetry relatively
small unit cell simple chemistry
Busing and Levy 1958
10High pressure single crystal diffraction
Single-crystal structure analysis of AlO(OH) at
50 GPa hydrogen atoms cannot be located
(Friedrich et al., 2007, Am. Min) a-AlOOH to d-
AlOOH at 18 GPa Diaspore metastable 30 GPa (and
reflections still narrow)
Diaspore crystal (30 x 20 x 10 µm³) at 52 GPa
11Compressibility (experiment and model)
Exp. and DFT B0 151(2) GPa Literature 85 -
230 GPa
Exp. Open symbols with error bars DFT Filled
symbols
B. Winkler et al. (2001) Eur. J. Mineral 13,
343. A. Friedrich et al. (2007) PCM 34, 145. A.
Friedrich et al. (2007) Am. Mineral. 92, 1640
12Diaspore
- structural behaviour very well predicted
- calc. Winkler et al (2001)
- exp. Friedrich et al. (Phys. Chem. Min, 2007
Am. Min., 2007) - predict smooth decrease of a to 9.5o at 50 GPa
13Hydrogen bond stretching motions of diaspore,
AlOOH
14Pressure-induced shift of n(OH)
- predicted shift does not follow correlation
established at ambient pressure - but O-H...O is slightly kinked in diaspore
- no experimental data yet
15Hydrogen bonding in diaspore
prediction of dispersion relation for
OH-stretching frequencies shows unexpectedly
large wave vector dependence implies non-local
dynamics
16European Synchrotron Radiation Facility
circumference 844 m energy 6 GeV 40 beamlines
http//www.saxier.org/aboutus/saxs.shtml
http//www.esrf.eu/AboutUs/GuidedTour/
17How to do the experiment?
kin
Q(1.11.11.1)
kout
18IXS set-up
Spot size 30 x 60 ?m2 (H x V)
sample
detector
E
i
Monochromator Si(n,n,n) reflection, n 7 -13
Q 89.98 ?1 tunable by temperature
E
f
Q 4 ?/ ? sin(?)
Analyzer Si(n,n,n) reflection, n 7 -13 Q
89.98 ?2 constant
? 2 d(T) sin?
?d/d ?E/E -?(T)?T ? 2.58.10-6 at RT
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20Diaspore
21IXS of hydrogen bonding in diaspore, AlOOH
- there is dispersion of the OH-stretching
vibration this is not a fully localised mode - dispersion can be rationalized by simple
electrostatic model of the H-H interaction
Winkler B. et al., PRL, 2008
22 23The hydrogarnet substitution
- Garnets X3Y2Z3O12
- X 8-fold coordinated
- Y 6-fold coordinated
- Z 4-fold coordinated
- O 4-fold coordinated
- GrossularCa3Al2Si3O12
- Pyrope Mg3Al2Si3O12
-
24Compressibility of garnets
25Compressibility of garnets
26The hydrogarnet substitution
- Katoite end-member hydrogrossular
- model for hydrogarnet substitution
- SiO4 replaced by (OH)4
- is there an unusual pressure-induced behaviour
of the OH bond ?
Nobes et al. (2000) Am. Min., 85, 1706-1715
27Katoite
- Compressibility well described
- compression mechanism for Al,Ca,O in agreement
with experiment - O-HO shows conventional behaviour
- hydro-pyrope always unstable w.r.t. components
due to small size of Mg - Nobes et al. (2000) Am. Min., 85, 1706-1715
- prompted new experiments by Lager et al., 2005
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29Katoite
Fluorinert Lager van Dreele, 1996 Theory
Nobes et al., 2000a, 2000b DAC Lager et al.,
2002 SME Lager et al., 2005
30Katoite
Theory Nobes et al., 2000a, 2000b SME Lager et
al., 2005
31Katoite IR (Lager et al., 2005)
32 33Zoisite
- two structurally closely related silicates
orthozoisite and clinozoisite - orthozoisite - nearly linear OH...O
- clinozoisite - kinked OH...O (167)
- hydrogen bond has intermediate strength (n(OH)
3100 cm-1 )
34Zoisite
- pressure-induced shifts are very different
- Winkler et al. (1989)
- orthozoisite dn/dP -34 cm-1/GPa
- Bradbury and Williams (2003)
- clinozoisite dn/dP -5 cm-1/GPa
- generally dn/dP -2 - -5 cm-1/GPa
- some exceptions with (small) blue shifts
Winkler et al. (1989)
35Model calculations
- DFT based
- plane wave basis set / norm conserving
pseudopotentials and DFPT using the CASTEP code - atom centered basis set (TZ2P) and finite
displacement approach using SIESTA code - athermal limit
- no correction for anharmonicity
- anharmonicity will generally red-shift the
stretching frequency (by 100 cm-1) - GGA will generally blue-shift the OH-stretching
frequency - recent study (Balan et al., 2008) has shown that
this results in fortuitous error cancellation
36Results
- very good agreement between independent models
and between models and experiment for structures,
elastic behaviour and lattice dynamics - pressure-dependence of n(OH) of zoisite is indeed
anomalous - theo -35 cm-1/GPa,
- exp -34 cm-1/GPa
- linear bond 2.5 elongation of O-H at 10 GPa in
orthozoisite - kinked bond in clinozoisite remains kinked, only
0.5 elongation
doesnt follow structure-frequency correlation
Winkler et al., Phys. Chem. Min (2008)
37 38Wadsleyite - structure
- ?-Mg2SiO4 - stable in the transition zone
(410-525 km depth) - structure orthorhombic or slightly monoclinic
(Smyth et al. 1997) - structure with fully ordered H-defects suggested
by Smyth (1994)
39Elastic constants
relaxed structure with total energy E0 and volume
V0 after straining the crystal, the energy is
V is the volume of the strained crystal
and
is the pressure taken at V0
is the elastic energy proportional to the strains
The elastic constants are then
40Elasticity of hydrous wadsleyite
- earlier study (Kiefer et al., 2001) used DFT-LDA
thermal correction for anhydrous wadsleyite - here DFT-GGA, both hydrous and anhydrous
wadsleyite - most drastic change in c55
- B decreases by 15
- exp Holl et al., 2008 get a decrease in B by 12
for partial hydration
41Wadsleyite - phonons
- exp. (Kohn et al., 2002, Deon and Kochmüller,
2008) - complex IR-spectra between
- 3200 3700 cm-1
- DFT model
- IR active modes at 3240 cm-1
- and 3265 cm-1
- OH-flip induces significant changes (modes at
3370 and 3590 cm-1) - pressure dependence
- nearly linear red-shift of 2 cm-1/GPa
42- Example V molar absorption coefficients
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45Take home messages
- Diffraction studies for the localisation of
hydrogen positions in minerals are demanding - Dont use spectroscopy-structure correlation
established at ambient pressure to infer hydrogen
positions at high pressures - DFT models work very well for hydrogen bonds
- (if all assumptions are fulfilled reasonably well
and the structural model is appropriate) - Recent developments allow to predict intensity
changes of Raman and IR spectra as a function of
pressure, compute molar absorption coefficients -
46Acknowledgements
- Frankfurt group, especially D. Wilson, A.
Friedrich - ESRF Michael Krisch and Alexei Bosak
- Keith Refson, Victor Milman, Julian Gale, R.
Nobes, E.V. Akhmatskaya, J. White - HydroMin collaboration E. Balan, K. Wright, M.
Blanchard, S. Delattre, M. Lazzeri, F. Mauri, J.
Ingrin - Funding DFG, BMBF, DAAD, ESF, CECAM, Psi-k