Calibrating experiments at atom-crushing pressures

doi:10.1126/science.abi8015

GSTDTAP > 气候变化

DOI	10.1126/science.abi8015
	Calibrating experiments at atom-crushing pressures
	Raymond Jeanloz
	2021-06-04
发表期刊	Science
出版年	2021
英文摘要	Experimentalists can now generate terapascal pressures in the laboratory, conditions sufficient to alter the structure of atoms and the nature of interatomic bonding ([ 1 ][1]). These are the pressures of planets' interiors and origins—7 TPa at Jupiter's center, 4 TPa in the middle of Saturn, 0.36 TPa for Earth's inner core—and planet growth involves impacts that generate pressures into the terapascal range ([ 2 ][2]). Understanding materials and their properties at such conditions provides key insights into how planetary bodies form and then evolve over billions of years. On page 1063 of this issue, Fratanduono et al. ([ 3 ][3]) establish a new calibration for such experiments, and their pressure-volume relations for gold (Au) and platinum (Pt) can now serve as reliable standards to >1 TPa. This is a notable contribution because the forces that stabilize the atom are of terapascal magnitude. For example, the quantum-mechanical pressure that keeps the negatively charged electron from being pulled into the positively charged nucleus of the Bohr atom is ℏ /(4π m ea5) = 2.3 TPa, with ℏ , m e, and a = 53 pm being Planck's constant divided by 2π, the mass of the electron, and the Bohr radius, respectively. Current experiments can thus match or even overwhelm ambient-condition quantum forces and profoundly change the properties of materials. For comparison, the pressure-volume work associated with compression to million-atmosphere (0.1 TPa) pressures amounts to electron volt changes in a material's energy, affecting the outer bonding electrons and hence the chemical properties of atoms ([ 4 ][4]). The trends of the periodic table become distorted under these conditions, with xenon, oxygen, and fluid hydrogen all transforming to metals and the “simple metal” sodium becoming a transparent, ionic salt (electride) by 0.2 TPa ([ 5 ][5], [ 6 ][6]). The more extreme conditions at the atomic unit of pressure, E H/ a 3 = 29 TPa, alter the internal energy of materials by kilo–electron volts ([ 7 ][7]). These conditions are the gateway to “kilovolt chemistry” in which core electrons—the deeper electron orbitals of the atom—engage in chemical bonding ([ 2 ][2], [ 8 ][8]). First-principles quantum mechanical calculations already predict unusual properties at multi-terapascal pressures—for example, with the stabilization of relatively open crystal-structure geometries for elemental iron as well as for a variety of compounds, despite the atoms being under high compression ([ 8 ][8]–[ 10 ][9]). Hydrogen is expected to be a metallic quantum-crystal at these conditions, with atomic separations approaching the de Broglie wavelength (atoms becoming quantum indistinct); the liquid state may exhibit exotic combinations of superconductivity and superfluidity ([ 11 ][10]). Motivated by these predictions, experimentalists have stretched their capabilities to achieve record high pressures under controlled laboratory conditions. Diamond-anvil cells are now approaching 1 TPa by compressing samples between cleverly sculpted diamond tips, holding the ∼1 µm3 (1 femtoliter) sample for (as far as we know) arbitrarily long periods of time ([ 12 ][11]). Room-temperature superconductivity was recently reported in a carbonaceous sulfur hydride compressed inside a diamond cell to 0.3 TPa ([ 13 ][12]); the impact on technology could be huge, if it leads to the synthesis of ambient-condition superconductors. By contrast, pulsed-power– and laser-driven dynamic compression can characterize much larger (cubic millimeter sized) samples to far higher pressures, but only for tens to hundreds of nanoseconds. For example, laser-driven ramp loading—in principle, a nearly isentropic compression—has taken carbon to 5 TPa, into the Thomas-Fermi-Dirac statistical atom regime; and spherically converging shocks have produced equation-of-state data to nearly 50 TPa, conditions that are relevant to understanding white-dwarf stars ([ 14 ][13], [ 15 ][14]). The diversity of techniques is noteworthy, with a variety of static versus dynamic means of generating high pressures and experimental diagnostics ranging from velocity interferometry to x-ray diffraction and spectroscopy. Calibration has thus become essential for comparing the different laboratory measurements, all the more so because the samples are probed over different temperatures and time scales by the different high-pressure methods. Fratanduono et al. 's pressure-volume measurements using both pulsed-power and laser-driven compression show that the two technologies, which can differ by an order of magnitude or more in sample dimensions and compression time, are in good agreement with each other ([ 3 ][3]). They also find general accord with diamond-cell reports but are able to provide improvements for the necessarily extrapolated calibrations of past experiments. It is both reassuring and impressive that measurements made over time scales spanning 12 orders of magnitude, from 10−8 s for laser-driven compression to 104 s or more for static high-pressure experiments, are in such good agreement with each other. Calibration allows completely independent experiments to be compared and even combined, not only validating but also substantially enhancing results because each method has its advantages and drawbacks. Short duration in the dynamic measurements invites nonequilibrium effects, whereas small samples and large stress gradients in the static experiments challenge reproducibility and quantification. One of the key reasons that robust calibration is essential is that these experiments provide tests of first-principles quantum mechanical calculations of material properties. To be clear, theory and experiment are closely symbiotic, with the laboratory work being guided by quantum calculations, which also help in the interpretation and application of the experimental results. At the same time, experiments provide important validation for theory, and discrepancies between theory and experiment help guide improvements in both. Working at extreme conditions, the community is moving toward more reliable predictions of material properties and phase stability at ambient conditions, advancing technology as well as fundamental understanding. The work also helps us to better understand planets, the platforms on which life can establish itself and evolve. 1. [↵][15]One terapascal corresponds to 10 million atmospheres pressure. 2. [↵][16]1. R. Jeanloz et al ., Proc. Natl. Acad. Sci. U.S.A. 104, 9172 (2007). [OpenUrl][17][Abstract/FREE Full Text][18] 3. [↵][19]1. D. E. Fratanduono et al ., Science 372, 1063 (2021). [OpenUrl][20][CrossRef][21][PubMed][22][Web of Science][23] 4. [↵][24]One electron volt = 96.5 kJ/mol. 5. [↵][25]1. Y. Ma et al ., Nature 458, 182 (2009). [OpenUrl][26][CrossRef][27][PubMed][28] 6. [↵][29]The electron-charge density becomes concentrated between the sodium ion cores at high pressure, so that the metal effectively transforms into a “salt” of Na+ cations bound to e − “anions” of increased charge density but without a nucleus. 7. [↵][30]Hartree's atomic unit of energy, E H = ℏ 2/( mea 2) = 27 eV, is the potential energy drawing the electron to the nucleus in the Bohr atom, and the unit of pressure is simply the energy density E H/ a 3 derived on dimensional grounds. 8. [↵][31]1. M. Miao, 2. Y. Sun, 3. E. Zurek, 4. H. Lin , Nat. Rev. Chem. 4, 508 (2020). [OpenUrl][32][FREE Full Text][33] 9. 1. C. J. Pickard, 2. R. J. Needs , J. Phys. Condens. Matter 21, 452205 (2009). [OpenUrl][34][CrossRef][35][PubMed][36] 10. [↵][37]1. L. Stixrude , Phys. Rev. Lett. 108, 055505 (2012). [OpenUrl][38][CrossRef][39][GeoRef][40][PubMed][41] 11. [↵][42]1. J. E. McMahon, 2. M. A. Morales, 3. C. Pierleoni, 4. D. M. Ceperley , Rev. Mod. Phys. 84, 1607 (2012). [OpenUrl][43] 12. [↵][44]1. N. Dubrovinskaia et al ., Sci. Adv. 2, e1600341 (2016). [OpenUrl][32][FREE Full Text][33] 13. [↵][45]1. E. Snider et al ., Nature 586, 373 (2020). [OpenUrl][46][CrossRef][35][PubMed][36] 14. [↵][47]1. R. F. Smith et al ., Nature 511, 330 (2014). [OpenUrl][38][CrossRef][39][GeoRef][40][PubMed][41] 15. [↵][48]1. A. L. Kritcher et al ., Nature 584, 51 (2020). [OpenUrl][49] Acknowledgments: I have benefitted from discussions with G. W. Collins, D. E. Fratanduono, N. Y. Yao, and E. Zurek. This work was supported by the National Nuclear Security Administration Center for Matter under Extreme Conditions and the National Science Foundation Physics Frontier Center for Matter at Atomic Pressure. 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领域	气候变化 ; 资源环境
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文献类型	期刊论文
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/329861
专题	气候变化资源环境科学
推荐引用方式 GB/T 7714	Raymond Jeanloz. Calibrating experiments at atom-crushing pressures[J]. Science,2021.
APA	Raymond Jeanloz.(2021).Calibrating experiments at atom-crushing pressures.Science.
MLA	Raymond Jeanloz."Calibrating experiments at atom-crushing pressures".Science (2021).