X-RAY RUNS: Apply for Beamtime
2017 Nov 1 - Dec 21
2018 Feb 7 - Apr 3
2018 Proposal/BTR deadline: 12/1/17
2018 Apr 11 - Jun 4
2018 Proposal/BTR deadline: 2/1/18
Research Experiences for Undergraduates (REU)
Zhongwu Wang†‡, Yusheng Zhao†, Kimberly Tait†§, Xiaozhou
Liao†, David Schiferl†, Changsheng Zha¶,
Robert T. Downs§, Jiang Qian†, Yuntian Zhu†, and Tongde Shen†
†Los Alamos National Laboratory, Los Alamos, NM 87545; §Department of
Geosciences, University of Arizona, Tucson, AZ 85721; and ¶Cornell High
Energy Synchrotron Source, Wilson Laboratory, Cornell University,
Ithaca, NY 14853
Communicated by Russell J. Hemley, Carnegie Institution of Washington,
Washington, DC, August 11, 2004 (received for review June 16, 2004)
A quenchable superhard high-pressure carbon phase was synthesized by
cold compression of carbon nanotubes. Carbon nanotubes were placed in a
diamond anvil cell, and x-ray diffraction measurements were conducted to
pressures of 100 GPa. A hexagonal carbon phase was formed at 75 GPa and
preserved at room conditions. X-ray and transmission electron microscopy
electron diffraction, as well as Raman spectroscopy at ambient
conditions, explicitly indicate that this phase is a sp3-rich hexagonal
carbon polymorph, rather than hexagonal diamond. The cell parameters
were refined to a0 2.496(4) Å, c0 4.123(8) Å, and V0 22.24(7) Å 3. There
is a significant ratio of defects in this nonhomogeneous sample that
contains regions with different stacking faults. In addition to the
possibly existing amorphous carbon, an average density was estimated to
be 3.6 0.2 g cm3, which is at least compatible to that of diamond (3.52
g cm3). The bulk modulus was determined to be 447 GPa at fixed K 4,
slightly greater than the reported value for diamond of 440–442 GPa. An
indented mark, along with radial cracks on the diamond anvils,
demonstrates that this hexagonal carbon is a superhard material, at
least comparable in hardness to cubic diamond.