New synchrotron-based single-crystal
methods for structural mineral physics
and materials science
Przemyslaw Dera
GeoSoilEnviro CARS,
The University of Chicago
Synchrotron High-pressure Mineral Physics and
Materials Science, Chicago, December 7, 2007
High pressure crystallography
Status Quo
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SXD high-pressure studies are very infrequent,
compared to high-pressure powder XRD because of:
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Lack of dedicated/optimized facilities
Lack of dedicated/custom software
More challenging sample preparation
“Fear or sophistication”
In USA there currently are no synchrotron facilities
offering routine high-pressure SXD capabilities
SXD experiments, if performed provide a very detailed
information about the structural changes at high
pressure
Because of lack of optimized experimental
methodology high-pressure SXD studies have been
limited to much lower pressure than powder diffraction
experiments
Needs, desires and motivation
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Many phase transitions identified using powder diffraction, or with
spectroscopic methods, for which there are no models of high-pressure phases.
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Powder diffraction HP experiments are becoming routine to perform, even in
the megabar pressure range. There is little that can be significantly improved.
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The detailed structural information is very hard to retrieve from powder
diffraction data, due to 1-dimensional character of the data and peak
overlapping and ambiguous indexing.
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SXD can take full advantage of lower intensity synchrotron beamlines (BM)
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Super-small beam size is not critical
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SXD data collection can be as fast as PXD
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SXD allows for a much better control of hydrostaticity
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SXD allows to work with multi-phase/crystal assemblages
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SXD decouples the phase transitions form grain size effects, grain-boundary
interactions etc.
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SXD carries much more information content and much more detailed
information
What is an SXD experiment
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Diffraction experiment performed with sample that contains
one or more single-crystal grains with size of >0.001mm
Data collection involves measurement of directions and
intensities of individual diffracted beams and corresponding
crystal orientations for a large population of reciprocal space
vectors.
Reciprocal space is reconstructed in three dimensions,
allowing for unambiguous indexing
Measured peak intensities are free from spatial and energy
overlaps
GOAL 1: make mSXD possible at any monochromatic high-pressure synchrotron station
equipped with area detector and rotation stage (instrument control and data analysis)
GOAL 2: Create custom (hardware and software) SXD solutions optimized for high-pressure
experiments
Alternative solutions
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mSXD with point detector
„ Simple data analysis
„ Accurate unite cell, and
intensities
„ Low background due to
diffracted beam collimation
„ Long data collection time
„ Very user-involving during
early data collection stages
„ Extensive sample rotation
needed
„ Real diffractometer needed
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mSXD with area detector
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Simple data analysis, but
presence of DAC
complicates it
Very fast data collection
Higher redundancy of data
Sample rotation needed
“Global picture” available
immediately
Can be done with very
simple rotation stage
mSXD with area detector
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Center the sample on rotation axis and with the beam
Collect diffraction images while rotating the sample
Determine detector coordinates and sample orientations for
each diffraction peak
Reconstruct the reciprocal space in 3-d
Determine the orientation matrix (index)
Predict peak positions in recorded diffraction images and
retrieve peak intensities (structure factor amplitudes)
Solve/refine the structure
vmSXD with area detector
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Ice, Dera et al. J. Synchr. Rad. (2005)
Scan the sample with white
beam to find the most
promising grain (Laue)
Perform series of
monochromatic exposures at
varied energies that cover
whole or part of the incident
spectrum
Assign peak energies using
appearance and disappearance
of peaks
Challenge: The method was
designed to study strain in
known phases, requires
knowledge of the unit cell
vmSXD with area detector:
reciprocal space reconstruction
MRI project scope
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Budget of ~$0.8M for three years
Two synchrotrons, three beamlines
APS (GSECARS + HPCAT), ALS (CALYPSO)
Three main techniques mSXD, vmSXD, pSXD
New hardware (dedicated goniometers, area detectors)
Customized and uniform software (IDL, EPICS)
For more information, please visit:
http://rruff.geo.arizona.edu/OLA/files/SXD.htm
MRI project at GSECARS:
13BMD
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BM, wide energy range (5-60 keV), KB microfocusing
(0.005x0.015)
MAR345 (MAR165 CCD) detector on a translation stage
Resistive heating capabilities
On line Brillouin and Raman Spectroscopy
mSXD and vmSXD capabilities
Rotation scan and energy scan data collection strategies
MRI project at GSECARS:
13IDD
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ID, energy range (15-40 keV), KB microfocusing
(0.005x0.008mm)
YAG and CO2 on-line laser heating systems
MAR165 CCD (MAR345) detector and sub-second exposures
Rotation scan and energy scan data collection strategies
MRI project at GSECARS:
13BMC
• 6-circle kappa geometry
• All axes have DC-servo motors with speeds up
to 16 degrees/second, allowing on-the-fly
scanning.
Pilatus
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Newport 6-circle
Fixed-energy monochromatic beam at 10,
15 and 30 keV
The expected focal spot size 0.025x0.025
mm.
Super fast PILATUS detector (200 Hz data
collection capabilities)
13IDD,
5 GPa,
Unit cell edge 56 A
Hydrostaticity issue:
•Gas loading (in commissioning)
•Laser annealing (available)
13BMD,
40 GPa,
0.01x0.01x0.003mm crystal
Summary
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SXD method is a very powerful technique that can be used to reveal
details of even very complicated crystal structures at high pressure,
complementary and usually superior to powder diffraction.
SXD can provide much more precise information for EOS studies (S.
Jacobsen)
The data collection process can be as simple as that of powder
experiments.
All of GSECARS experimental stations offer now SXD capabilities.
At GSECARS SXD can be combined with heating (laser or resistive) and
on-line spectroscopy (Brillouin and Raman)
Acknowledgements
MRI postdocs
L. Borkowski
B. Lavina
HPCAT:
G. Shen, P. Liermann, W..Yang
MRI grant
M. Nicol
R.T.Downs
GSECARS:
M. Rivers
W. Prakapenka
P. Eng
S. Ghose
COMPRES
NSF DMR MRI program