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Bigger, Better Diamond Crystals PDF Print E-mail
Researchers at the Geophysical Laboratory have developed a technique for improving the properties of diamond, simplifying the process of making high-quality diamond for scientific applications, electronic components, cutting tools, and even quantum computers. The results are published in the current Online Edition of the Proceedings of the National Academy of Sciences.

Impurities and defects in diamond can be purged by annealing, but this can turn diamond to graphite. In order to prevent graphitization, diamond treatments have previously required high pressures (up to 60,000 times atmospheric pressure) during annealing, which is costly and limits the size and quantities of diamond treated. Yufei Meng and colleagues used CVD to grow diamond in their experiments. Unlike other methods, which mimic the high pressures deep within the earth where natural diamond is formed, the CVD method produces single-crystal diamond at low pressure. The resulting diamond, which can be grown very rapidly, have precisely controlled compositions and comparatively few defects.

The Carnegie team then annealed the diamond at temperatures up to 2000° C using a microwave plasma at pressures below atmospheric pressure. The crystals, which are originally yellow-brown if produced at very high growth rates, turned colorless or light pink. Despite the absence of stabilizing pressure there was minimal graphitization. Using analytical methods such as photoluminescence and absorption spectroscopy, the researchers were also able to identify the specific crystal defects that caused the color changes. In particular, the rosy pink color is produced by structures called nitrogen vacancy (NV) centers, where nitrogen atoms take the place of carbon atoms in the crystal lattice. [Y. Meng, et al., Proc. Nat. Acad. Sci., 105, 17620-17625 (2008)]

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Electronic heat trap found in deep Earth PDF Print E-mail
The key to understanding Earth’s evolution, including how our atmosphere gained oxygen and how volcanoes and earthquakes form is too look deep, really deep, into the lower mantle some 400 to 1,800 miles (660 to 2,900 kilometers) below the surface. Researchers , led by Alexander Goncharov (Geophysical Laboratory) and including Carnegie Summer Scholar Ben Haugen (University of Colorado) and new CDAC partner Steven Jacobsen (Northwestern), mimicked conditions of these depths and recently discovered that the concentration of highly oxidized iron (Fe3+) in the two major mantle minerals—silicate perovskite and ferropericlase—is key to moving radiative heat in that region, and that influences material movement throughout the planet. They also discovered that less oxidized iron (Fe2+) has much less effect than expected — 2 to 5 times lower than previous models suggested. The results, which are reported Nature, call into question current models of mantle dynamics.

The team developed a new optical spectroscopy system to reveal how matter absorbs heat from infrared through ultraviolet wavelengths; in addition they measured how energy is dissipated. They subjected the minerals to mantle pressures—up to 1.3 million atmospheres at room temperature and subjected ferropericlase to 590,000 atmospheres at temperatures up to 1160°F. The scientists found that heat absorption is governed by the concentration of ferric (Fe3+) iron in silicate perovskite and ferropericlase. They also noted changes in absorption related to spin-state transition, but the effects were smaller than previously believed. Spin transition occurs when electrons are bunched closely together under severe pressures and the spinning electrons are forced to pair up from unpaired electrons—a high-spin state—to paired electrons—a low-spin state. Their results for silicate perovskite in the visible and near infrared for radiative heat absorption showed that it is dominated by the charge transfer of electrons during oxidation—when electrons are lost— in the oxide O-Fe3+ [Goncharov, et al., Nature, 456, 231-234 (2008)].
Workshop in Honor of NSLS High Pressure Beamline Scientists PDF Print E-mail
The Workshop on Advances in High-Pressure Science using Synchrotron X-rays, held on October 4th at the National Synchrotron Light Source, was a tremendous success. The workshop was organized in honor of Jingzhu Hu and Quanzhong Guo in celebration of their retirement after up to 18 years of dedicated service to the high-pressure community. Hu was the beamline scientist of X17C, the first synchrotron beamline in the world dedicated to high-pressure research. The beamline, which was created and managed by Carnegie for many years, was later complemented by X17B, which was led by Guo. 47 participants from 18 institutions were present at the workshop. CDAC partners Yangzhang Ma (Texas Tech) and Jie Li (University of Illinois, Urbana-Champaign), presented talks, along with Carnegie scientists Ho-kwang Mao, Alexander Goncharov, Yingwei Fei, and Michelle Weinberger.

 


  • Lashley, J. C., S. M. Shapiro, B. L. Winn, C. P. Opeil, M. E. Manley, A. Atlas, W. Ratcliff, T. Park, R. A. Fisher, B. Mihaila, P. Riseborough, E. K. H. Salje, and J. L. Smith, Observation of a continuous phase transition in a shape-memory alloy, Phys. Rev. Lett, 135703 (2008).
  • Hazen, R. M., D. Papineau, W. Bleeker, R. T. Downs, J. M. Ferry, T. J. McCoy, D. A. Sverjensky, and H. Yang, Mineral evloution, Am. Mineral., 93, 1693-1720 (2008).
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Welcome

CDAC is an interdisciplinary center headquartered at the Geophysical Laboratory of the Carnegie Institution of Washington. Our goals are to advance and perfect an extensive set of high P-T techniques and unique facilities, to perform key studies on a broad range of important materials in newly-accessible P-T regimes, and to integrate and coordinate static, dynamic and theoretical results for Stewardship Science applications.