Synchrotron highpressure highlow temperature techniques

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Synchrotron high-pressure high/low temperature
techniques
ID27 team J.P. Perrillat, G. Garbarino, W.
Crichton, P. Bouvier, S. Bauchau
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• Outline
• Introduction XRD Beamlines -
• Research examples AND Limitations
• Conclusion

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HP synchrotron beamlines are multidisciplinary
instruments
ID27 Fully dedicated to HP XRD experiments In
operation since 2006 in replacement of ID30
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Beamline ID27-ESRF
ESRF 6 GeV
Sample environment
X-ray Source
Detectors
Mirrors
Monochromator
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The Paris-Edinburgh large volume cell The only
monochromatic LVC Pressure up to 17 GPa on 5
mm3 sample volume Resistive heating up to
2300 K Main X-ray technique X-ray diffraction on
powders/liquids/amorphous materials
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One remark
Structure determination at very HP (Pgt1.2 Mbar)
requires a very intense and very small X-ray beam.
ID30
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Very intense micro-focused beam (2 microns) using
two KB multi-layer mirrors at short wavelengths
0.15lt?lt0.4 Å
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Kirkpatrick-Baez focusing mirrors
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High precision at ultra-high pressures case of
iron
Interest ? Geophysics Main constituent of
Earths core ? Physics Magnetism
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High precision at ultra-high pressures case of
iron
Fe W in He at 199 GPa
Ref A. Dewaele, P. Loubeyre, F. Occelli, M.
Mezouar, Phys. Rev. Lett. 97, 215504 (2006)
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Limitation The diamond anvil cell not the X-ray
beam!
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Structure of metallic oxygen?
? (insulator) ? ? (metal) transition at P100 GPa
5 micron single crystal of oxygen in a 20 micron
gasket hole (helium pressure medium)
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Poor data quality, high background from the DAC
G. Weck,S. Desgreniers,P. Loubeyre, M.
Mezouar ID30, 139 GPa
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Structure of metallic oxygen?
ID27
Data of much higher quality/ID30 BUT not enough
to solve the structure ??? transition degrades
the single X-tal quality (large rocking curves
gt1?)
G. Weck,S. Desgreniers,P. Loubeyre, M.
Mezouar ID27, 139 GPa
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• More single X-tal data of the ? phase
• (different orientations)
• Two possible monoclinic space
• groups C2/c and C2/m

Raman C2/c allows only 6 active Raman modes ?
? phase has the C2/m symmetry
G. Weck,S. Desgreniers,P. Loubeyre, M. Mezouar,
PRL, in press
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Limitation Single crystal quality! (not the
X-ray beam) Solution (In situ) HP/HT single
X-tal growth
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P-T Phase diagram of sodium
Ref Gregoryanz E, Degtyareva O, Somayazulu M,
Hemley RJ, Mao HK, PRL, 94,185502 (2005)
It is possible to grow a single x-tal of Na at
120 GPa near RT and perform a full structural
determination.
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Examples of high quality single x-tal
diffraction patterns of Na collected at
ID27 Beamsize 3?m ?0.3738 Å Sample volume
10x10x5 ?m3
Phase diagram around the melting curve minimum
at P117 GPa ?Many new and unpredicted structures
of very high complexity
Ref E. Gregoryanz, L. Lundegaard, M.I.
McMahon,C. Guillaume, R.J. Nelmes, M.Mezouar,
Science, 320,1054 (2008)
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Hydrogen at high very high pressure
At atmospheric conditions Hydrogen is a
fundamental element for biology, chemistry and
physics At high pressure Hydrogen is of high
interest for physics and geophysics -Principal
constituent of giant planets such as Jupiter
(90) -Prediction of the existence of a metallic
form of hydrogen by Eugene Wigner in 1935
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Phase diagrams of H2 and D2 from spectroscopic
measurements up to 200 GPa (1994)
3 phases identified but no structural
determination of phase II and III. Phase I hcp
lattice of freely-rotating molecules Phase II
and III ??
Ref. R. Hemley, M. Hanfland, et al.
(Geophysical Lab., Washington)
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Single crystal of H2 in helium pressure medium
Equation of state of hydrogen I up to 120 GPa at
ESRF ID09 (1996) BUT using the EDX technique ? no
structural determination
Ref. P. Loubeyre et al., Nature, 383, 702 (1996)
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For almost 10 years , all attempts to solve the
structure of phase II failed Too many
experimental difficulties High pressure - Low Z
material - Extremely reactive Hydrogen is
certainly the most difficult sample to study with
X-rays at very HP.
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• Structure solved in 2005 by a combination of
  mononochromatic XRD
• from ID30/ID09 and neutron data from LLB (Igor
  Goncharenko)
• ?Phase II has an hcp incommensurate structure
  with a local orientational order
• (Pa3 local symmetry).

More details in
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Phase III of hydrogen not reachable at ID30
because of the too large beam size ? ID27
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Limitations ?Control of crystal
orientations ?Compton scattering from
diamonds
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Only result so far Evolution of the 100
d-spacing of hydrogen up to phase III
Structure of phase III is still an open question
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Melting at HP

•  The accurate determination of melting curves is
  of fundamental
• interest in different research areas such as
  physics and geophysics.
• 2 classical experimental methods
• Optical measurements in the laser heated diamond
  anvil cell
• Melting induced by shock compression
• Ab-initio calculations
• Large temperature discrepancies between these 3
  methods
• ? ?Tgt1500 K at 2 megabar for iron.

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Melting curve of lead
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• New approach developed at beamline ID27
• Fast in situ X-ray diffraction in the
  double-sided laser heated diamond anvil cell.
• Advantages
• ? It is sensitive to the bulk of the sample
  (surface)
• The XRD measurements are performed at
  thermodynamic equilibrium (shock)
• ? It uses well established pyrometric methods
• Also important
• X-ray diffraction in the laser heated DAC
  provides an unambiguous signature
• of the melt at thermodynamic equilibrium and
  identifies chemical reactions if any.

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Experimental method
? The sample is heated on both sides by 2 focused
YAG laser providing a maximum power of 80 Watts.
? The 2 lasers are slightly defocused in order
to create a large and homogenous heated area of
about 30 microns. ? The temperature is
measured at the center of the hot spot by
analyzing the pyrometric signal emitted by a 2x2
µm2 area ? The X-ray beam is highly focused on
a 3x3 µm2 area which is 10 times smaller than the
heated area ? The X-ray beam is perfectly
aligned at the center of the laser hot spot
(within 1 µm precision) by a direct visualization
of the fluorescence signal created by the X-ray
beam on a CCD camera
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Experimental method
? The temperature is gradually increased by
tuning the laser power ? For each increment of
the laser power, the temperature is measured by
pyrometry and a diffraction pattern is
automatically collected -The temperature
increment is 30 K -The typical cycle time is 2
seconds ? The pressure is measured in situ using
NaCl as pressure marker More than 5000 XRD
patterns have been collected!
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Experimental method
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Melting at P61 GPa NaCl pressure medium E33
keV Focused X-ray beam of 3x3 ?m2 Mar CCD
detector 1 frame/2 sec.
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Ref A. Dewaele, M. Mezouar, N. Guignot, P.
Loubeyre, Phys. Rev. B 76, 144106 (2007)
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Limitations Detector commercial CCD detectors
are too slow for sub-second time resolved
experiments. ?the photon flux is not the
problem Sample containers major problems in
laser heated DACs ? liquid
confinement and chemical reactions Possible
solution optimized containers
Al2O3
O2
Au
Ref. R. Benedetti et al., Appl. Phys. Lett., 92,
141903 (2008)
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• Conclusion
• ? HP Beamlines with outstanding performance in
  terms of photon flux and focusing
• capabilities are in operation
• ?Limitations are mostly coming from external
  factors
• Max. P Limited by the DAC
• ?Background from the DAC for light elements
  studies
• ?Sample preparation single X-tal growth at
  megabar pressures,
• ?Solutions
• Use of complementary techniques Neutrons (for
  low P), Raman, Brillouin,
• IXS,
• ?micro-assemblies for laser heated DAC
• ?Improved sample environment laboratories on
  site HPSynch at APS,
• PECS (partnership for science at extreme
  conditions) at the ESRF