Articles

February 23, 2012 12:25 PM

In the superconducting iron chalcogenides, a second superconducting phase suddenly reemerges above 11.5 GPa, after the Tc drops from the first maximum of 32K at 1 GPa. The Tc of the re-emerging superconducting phase is higher than the first maximum, reaching 48.0–48.7K for two materials studies. HPCAT experiments show that the basic structure of these compounds was not changed under the extreme pressure and thus further research is needed to determine the origin of the re-appearance at the structural level. The result is published in Nature, Feb. 22, 2012. 
CIW-Geophysical Laboratory
, Advanced Photon Source
(Figure: Pressure dependence of the superconducting temperature)

February 17, 2012 11:57 AM

A miniature X-ray emission spectrometer has been successfully commissioned by a team of researchers from the University of Washington, LLNL and HPCAT. The spectrometer, based on a coarsely diced approximate of the Johansson optics, contains six small flat Ge ( 3 3 1 ) crystals, which are ~7.4cm away from sample and have a total solid angle of ~50msr, roughly equivalent to that of six traditional spherically bent crystal analyzers. The overall energy resolution is ~1.3eV. The new XES spectrometer provides improved efficiency in X-ray emission spectroscopy (XES) measurements, which has been demonstrated in RXES measurements for Pr at high pressures in a diamond anvil cell. (Pacold et. al. J. Synchrotron Rad (2012),  19). (Photograph of the miniXES spectrometer at 16ID-D with DAC and Pilatus in place)

 

February 14, 2012 10:29 AM

White x-ray radiography measurement combined with Paris-Edinburgh cell at the HPCAT beamline 16BM-B provides a capability of investigating viscosity of liquid at high pressure and high temperature conoditions using falling sphere viscometer technique.  A preliminary experiment was carried out for a silicate melt at 3.5 GPa and 1600 °C.  Pt sphere smoothly fell in the silicate melt. Viscosity can be obtained by deriving the falling velocity of the Pt sphere. Video

January 24, 2012 10:31 AM

Sodium displays a great deal of surprising behaviors under high pressure such as melting at room temperature at 118GPa and transition to an insulator over 200GPa. Recent HPCAT experiments measured plasmon excitations of sodium from ambient pressure up to 97GPa using the momentum-dependent inelastic X-ray scattering technique.  The square of zero-momentum plasmon energy increases linearly with densification up to 1.5-fold (~5GPa), which agrees well with a simple free-electron model prediction. From 1.5-fold to 3.7-fold densification at 97GPa, the linear relation curves towards the density axis. However, this deviation can still be explained by a simple metal model. These results showed that even under multiple fold densification the solid Na of both bcc and fcc symmetry can be regarded as simple metals.

November 8, 2011 01:26 PM

The photo left shows a sample of KC1O3  powder inside a diamond anvil cell with reddish damage spots (near the center) of molecular oxygen after x-ray bombardment at 15 GPa. The clear bubbles are ruby spheres. 

A novel method to load oxygen in a sealed diamond anvil cell, via the x-ray induced decomposition of potassium chlorate (KClO3) is demonstrated. It is anticipated that this technique will be useful in loading even more challenging, difficult-to-load gases such as hydrogen and also to load multiple gases.

Michael Pravica, Ligang Bai, Changyong Park, Yu Liu, Martin Galley, John Robinson, and Neelanjan Bhattacharya

Rev. Sci. Instrum. 82, 106102 (2011)

November 4, 2011 11:14 AM

 Diagram of the diamond anvil cell experiment

An amorphous diamond—one that lacks the crystalline structure that makes diamonds cleavable, but is every bit as hard—has been created by a team of researchers using a High Pressure Collaborative Access Team x-ray beamline at the U.S. Department of Energy Office of Science’s Advanced Photon Source.
http://www.aps.anl.gov/Science/Highlights/Content/APS_SCIENCE_20111026C.php
 

September 19, 2011 09:45 AM

Phonon DOS and pDOS of ordered FeV (green) are clearly softened compared to the disordered phase (black).      

September 19, 2011 04:25 PM

Novel Magnetic Material operates under Extreme Stress Conditions

See: D. Haskel, G. Fabbris N. M. Souza-Neto, M. van Veenendaal,  G. Shen, A. E. Smith, M. A. Subramanian, “Stability of the ferromagnetic ground state of oxide insulator La2MnNiO6 against large compressive stress,” Phys. Rev. B 84, 100403 (2011)