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
Geophysics Biology Near RP,RT 3.5 Mbar T<6000 K HP synchrotron beamlines are multidisciplinary instruments ID27: Fully dedicated to HP XRD experiments In operation since 2006 in replacement of ID30
Beamline ID27-ESRF ESRF 6 GeV Sample environment X-ray Source Detectors Mirrors Monochromator
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 mm3 sample volume • Resistive heating up to 2300 K Main X-ray technique: X-ray diffraction on powders/liquids/amorphous materials
One remark: Structure determination at very HP (P>1.2 Mbar) requires a very intense and very small X-ray beam. ID30
ID30 ID27 2 m 12 m -- -- Very intense micro-focused beam (2 microns) using two KB multi-layer mirrors at short wavelengths: 0.15<<0.4 Å
Micro-grains of iron and tungsten in helium pressure Medium 35 µ m P gauge (ruby ball) High precision at ultra-high pressures: case of iron Interest: Geophysics: Main constituent of Earth’s core Physics: Magnetism
Fe W Fe W 2q High precision at ultra-high pressures: case of iron Fe+Win He at 199 GPa Ref: A. Dewaele, P. Loubeyre, F. Occelli, M. Mezouar, Phys. Rev. Lett. 97, 215504 (2006)
Max. P at ID30 Diamond breakage Limitation: The diamond anvil cell not the X-ray beam!
Structure of metallic oxygen? (insulator) (metal) transition at P~100 GPa 5 micron single crystal of oxygen in a 20 micron gasket hole (helium pressure medium)
ID30 O2 Poor data quality, high background from the DAC G. Weck,S. Desgreniers,P. Loubeyre, M. Mezouar ID30, 139 GPa
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 >1) G. Weck,S. Desgreniers,P. Loubeyre, M. Mezouar ID27, 139 GPa
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
Limitation: Single crystal quality! (not the X-ray beam) Solution: (In situ) HP/HT single X-tal growth
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.
Examples of high quality single x-tal diffraction patterns of Na collected at ID27 Beamsize~ 3m; =0.3738 Å Sample volume~ 10x10x5 m3 Phase diagram around the melting curve minimum at P=117 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)
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
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)
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)
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
100 10 µm single crystal of H2 in helium pressure medium P>150 GPa Very weak diffraction peak of H2 at P=150 GPa 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
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 • T>1500 K at 2 megabar for iron.
Theory (Cricchio et al. MD) ---- Melting curve of lead 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 Large discrepancy in melting temperatures T>1000 K at P=80 GPa
New approach developed at beamline ID27 : • Fastin 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 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 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
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
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, 144106 (2007)
Limitations: Detector: commercial CCD detectors are too slow for sub-second time resolved experiments. thephoton 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)
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