Synchrotron high-pressure high/low temperature techniques ID27 team: J.P. Perrillat, G. Garbarino, W. Crichton, P. Bouvier, S. Bauchau

Outline  Introduction – XRD Beamlines -  Research examples AND Limitations  Conclusion

Near RP,RT3.5 Mbar T<6000 K Biology Geophysics HP synchrotron beamlines are multidisciplinary instruments ID27: Fully dedicated to HP XRD experiments In operation since 2006 in replacement of ID30

Detectors Sample environment MirrorsMonochromator X-ray Source ESRF 6 GeV Beamline ID27-ESRF

Diamond anvil cell Pressures up to 3 Mbar High temperatures Resistive heating up to 1000 K Laser heating T>4000 K Low temperature down to 5 K (Helium cryostat) Main X-ray techniques X-Ray single X-tal and powder diffraction in monochromatic mode

The Paris-Edinburgh large volume cell: The only monochromatic LVC Pressure up to 17 GPa on 5 mm 3 sample volume Resistive heating up to 2300 K Main X-ray technique: X-ray diffraction on powders/liquids/amorphous materials

Structure determination at very HP (P>1.2 Mbar) requires a very intense and very small X-ray beam. ID30 One remark:

2  m  m -- ID30 ID27 Very intense micro-focused beam (2 microns) using two KB multi-layer mirrors at short wavelengths: 0.15< <0.4 Å

Kirkpatrick-Baez focusing mirrors

35 µ m P gauge (ruby ball) Micro-grains of iron and tungsten in helium pressure Medium High precision at ultra-high pressures: case of iron Interest:  Geophysics: Main constituent of Earth’s core  Physics: Magnetism

High precision at ultra-high pressures: case of iron Fe W W 22 Ref: A. Dewaele, P. Loubeyre, F. Occelli, M. Mezouar, Phys. Rev. Lett. 97, (2006) Fe + W in He at 199 GPa

Diamond breakage Max. P at ID30 Limitation: The diamond anvil cell not the X-ray beam!

5 micron single crystal of oxygen in a 20 micron gasket hole (helium pressure medium) Structure of metallic oxygen?  (insulator)   (metal) transition at P~100 GPa

ID30 O2O2 G. Weck,S. Desgreniers,P. Loubeyre, M. Mezouar ID30, 139 GPa Poor data quality, high background from the DAC

G. Weck,S. Desgreniers,P. Loubeyre, M. Mezouar ID27, 139 GPa ID27 Data of much higher quality/ID30 BUT not enough to solve the structure…  transition degrades the single X-tal quality (large rocking curves >1  ) Structure of metallic oxygen?

+ Raman C2/c allows only 6 active Raman modes   phase has the C2/m symmetry More single X-tal data of the  phase (different orientations)  Two possible monoclinic space groups: C2/c and C2/m G. Weck,S. Desgreniers,P. Loubeyre, M. Mezouar, PRL, in press

Limitation: Single crystal quality! (not the X-ray beam) Solution: (In situ) HP/HT single X-tal growth

P-T Phase diagram of sodium It is possible to grow a single x-tal of Na at ~120 GPa near RT and perform a full structural determination. Ref: Gregoryanz E, Degtyareva O, Somayazulu M, Hemley RJ, Mao HK, PRL, 94, (2005)

Ref: E. Gregoryanz, L. Lundegaard, M.I. McMahon,C. Guillaume, R.J. Nelmes, M.Mezouar, Science, 320,1054 (2008) Examples of high quality single x-tal diffraction patterns of Na collected at ID27 Beamsize~ 3  m; = Å Sample volume~ 10x10x5  m 3 Phase diagram around the melting curve minimum at P=117 GPa  Many new and unpredicted structures of very high complexity

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 Hydrogen at high very high pressure

Ref. : R. Hemley, M. Hanfland, et al. (Geophysical Lab., Washington) Phase diagrams of H 2 and D 2 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 ??

Equation of state of hydrogen I up to 120 GPa at ESRF ID09 (1996) BUT using the EDX technique  no structural determination Single crystal of H 2 in helium pressure medium Ref.: P. Loubeyre et al., Nature, 383, 702 (1996)

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.

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:

ID30 Phase III of hydrogen not reachable at ID30 because of the too large beam size  ID27

10 µm single crystal of H 2 in helium pressure medium P>150 GPa Very weak diffraction peak of H 2 at P=150 GPa 100 Limitations:  Control of crystal orientations  Compton scattering from diamonds

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…

Experimental method - Double-sided laser heating system at ID27 Dedicated experimental hutch – The system is mounted on a high stability 5 tons marble

Double-sided laser heating system at ID27 Accessible PT domain for in situ powder XRD: P>2 Mbar; T>4000 K

Laser beam X-ray beam Sample Imaging and T measurement

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   T>1500 K at 2 megabar for iron. Melting at HP

Lead is a good candidate for melting studies using XRD :  good YAG laser absorber  high Z material  melting curve determined by optical DAC technique, shock compression and calculated using ab-initio methods in a wide pressure domain Theory (Cricchio et al. MD) ---- Large discrepancy in melting temperatures  T>1000 K at P=80 GPa Melting curve of lead

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.

Laser beam X-ray beam Double sided laser heating of iron in argon at 1.2 Mbar in a 60  m gasket hole Collaboration: R. Boehler, MPI Mainz D. Errandonea, Univ. of Valencia  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 µm 2 area  The X-ray beam is highly focused on a 3x3 µm 2 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 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! Experimental method

P=61 GPa Experimental method

Melting at P=61 GPa NaCl pressure medium E=33 keV Focused X-ray beam of 3x3  m2 Mar CCD detector 1 frame/2 sec.

Melting curve in good agreement with theory but in contradiction with previous experimental data (Shock, or optically in DAC) Ref: A. Dewaele, M. Mezouar, N. Guignot, P. Loubeyre, Phys. Rev. B 76, (2007)

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: Ref.: R. Benedetti et al., Appl. Phys. Lett., 92, (2008) Al2O3 O2 Au

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