Articles

February 14, 2012 11:29 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 11:31 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 02:26 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 12:14 PM

 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 10:45 AM

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

September 19, 2011 05:25 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)

June 23, 2011 05:40 PM

Researchers Xiao-Jia Chen, Viktor Struzhkin, and Ho-Kwang Mao from Carnegie and Yue Meng from HPCAT, along with collaborators from China, designed delicate experiments to obtain a complete high-pressure phase diagram of compressed Ge. Their results, published in Physical Review Letters, show that under a pressure of 66 GPa, Ge undergoes a structural change from a metallic white tin structure to an orthorhombic Imma structure. It then undergoes another change under pressure of 90 GPa to the simple hexagonal structure.

June 17, 2011 03:29 PM