New synchrotronNew synchrotron--based singlebased single--crystalcrystalmethods for structural mineral physics methods for structural mineral physics and materials scienceand materials science

Przemyslaw DeraGeoSoilEnviro CARS, The University of Chicago

Synchrotron High-pressure Mineral Physics and Materials Science, Chicago, December 7, 2007

High pressure crystallography Status Quo

SXD high-pressure studies are very infrequent, compared to high-pressure powder XRD because of:

Lack of dedicated/optimized facilitiesLack of dedicated/custom softwareMore challenging sample preparation“Fear or sophistication”

In USA there currently are no synchrotron facilities offering routine high-pressure SXD capabilitiesSXD experiments, if performed provide a very detailed information about the structural changes at high pressureBecause of lack of optimized experimental methodology high-pressure SXD studies have been limited to much lower pressure than powder diffraction experiments

Needs, desires and motivationMany phase transitions identified using powder diffraction, or with spectroscopic methods, for which there are no models of high-pressure phases.Powder diffraction HP experiments are becoming routine to perform, even in the megabar pressure range. There is little that can be significantly improved.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.SXD can take full advantage of lower intensity synchrotron beamlines (BM)Super-small beam size is not criticalSXD data collection can be as fast as PXDSXD allows for a much better control of hydrostaticitySXD allows to work with multi-phase/crystal assemblagesSXD decouples the phase transitions form grain size effects, grain-boundary interactions etc.SXD carries much more information content and much more detailedinformation

What is an SXD experiment

Diffraction experiment performed with sample that contains one or more single-crystal grains with size of >0.001mmData 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 indexingMeasured 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

mSXD with point detectorSimple data analysisAccurate unite cell, and intensitiesLow background due to diffracted beam collimationLong data collection timeVery user-involving during early data collection stagesExtensive sample rotation needed Real diffractometer needed

mSXD with area detectorSimple data analysis, but presence of DAC complicates itVery fast data collection Higher redundancy of dataSample rotation needed“Global picture” available immediatelyCan be done with very simple rotation stage

mSXD with area detectorCenter the sample on rotation axis and with the beamCollect diffraction images while rotating the sampleDetermine detector coordinates and sample orientations for each diffraction peakReconstruct the reciprocal space in 3-dDetermine the orientation matrix (index)Predict peak positions in recorded diffraction images and retrieve peak intensities (structure factor amplitudes)Solve/refine the structure

Ice, Dera et al. J. Synchr. Rad. (2005)

1. Scan the sample with white beam to find the most promising grain (Laue)

2. Perform series of monochromatic exposures at varied energies that cover whole or part of the incident spectrum

3. 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

vmSXD with area detector: reciprocal space reconstruction

MRI project scopeBudget of ~$0.8M for three yearsTwo synchrotrons, three beamlines

APS (GSECARS + HPCAT), ALS (CALYPSO)Three main techniques mSXD, vmSXD, pSXDNew 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

BM, wide energy range (5-60 keV), KB microfocusing(0.005x0.015)MAR345 (MAR165 CCD) detector on a translation stageResistive heating capabilitiesOn line Brillouin and Raman SpectroscopymSXD and vmSXD capabilities Rotation scan and energy scan data collection strategies

MRI project at GSECARS: 13IDD

ID, energy range (15-40 keV), KB microfocusing(0.005x0.008mm)YAG and CO2 on-line laser heating systemsMAR165 CCD (MAR345) detector and sub-second exposuresRotation scan and energy scan data collection strategies

MRI project at GSECARS: 13BMC

Newport 6-circle

Pilatus

Fixed-energy monochromatic beam at 10, 15 and 30 keVThe expected focal spot size 0.025x0.025 mm. Super fast PILATUS detector (200 Hz data collection capabilities)

• 6-circle kappa geometry• All axes have DC-servo motors with speeds up to 16 degrees/second, allowing on-the-fly scanning.

13IDD,5 GPa,Unit cell edge 56 A

13BMD,40 GPa,0.01x0.01x0.003mm crystal

Hydrostaticity issue:

•Gas loading (in commissioning)•Laser annealing (available)

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)

Summary

MRI postdocsL. BorkowskiB. Lavina

MRI grantM. NicolR.T.Downs

COMPRESNSF DMR MRI program

HPCAT:G. Shen, P. Liermann, W..Yang

GSECARS:M. RiversW. PrakapenkaP. EngS. Ghose

Acknowledgements