November 29, 2012 05:45 PM

Silicon is abundant in nature and arguably the most widely used material nowadays. Recent HPCAT experiments show that silicon displays an intriguing precursor lattice at high pressure, which provides a clue for understanding the process and mechanism of phase transitions in solids.  The results from high-pressure single crystal diffraction show that an embryonic phase can dynamically co-exist with the host lattice through collective motions. This collective mechanism for the phase transition goes beyond previously considered reconstructive or displacive processes and provides a novel picture of the underlying dynamics. This work opens a new avenue for exploring precursor phenomena in phase transitions which may be more common than previously thought.

November 5, 2012 05:14 PM

At high pressures, calcium (Ca) not only displays very rich structural changes but also holds the record for the highest superconducting critical temperature (Tc = 26 K) among elemental materials; furthermore Ca is a very active test case of modern theories and experiments, where a number of paradoxes arise based on density functional theory calculations related to the stability of its simple cubic phase. Using synchrotron high-pressure x-ray diffraction at cryogenic temperatures, we have established a new phase diagram for calcium up to 110 GPa and 5-300 K. We discovered the long-sought for theoretically predicted β-tin structured calcium with I41/amd symmetry at 35 GPa in a small low temperature range below 10K, thus resolving the enigma of absence of this lowest enthalpy phase.

Fig. 1 Proposed phase diagram of Ca at high pressure and low temperature.

August 3, 2012 10:37 AM

Research at the U.S. Department of Energy Office of Science’s Advanced Photon Source (APS) by researchers from Argonne National Laboratory, the Brazilian Synchrotron Light Laboratory, the Carnegie Institution of Washington, and Commissariat à l'énergie atomique-CEA (France) has shown that gaining valence information requires a lot more work when it comes to mixed-valence systems. Their results have been published in the journal Physical Review Letters. (more...)

July 23, 2012 12:15 PM

A Carnegie scientist's observations have led the way to stabilizing tungsten hydrides under high pressure. (more...)

July 2, 2012 03:33 PM

A collaborative experimental effort with Carnegie researchers has discovered unknown properties of a computer memory material that will allow for faster data transfer with a higher capacity of data stored. (more…)(

June 29, 2012 09:06 AM

The metal-insulator transition at 105Kin the T’-La4Ni3O8 is associated with significant changes of lattice parameters. These changes are consistent with the model of a temperature-driven high-spin to low-spin transition at Tt.  The high pressure structural study at HPCAT reveals that a new T+structure is stabilized under P>21 GPa. The presence of isolated Ni sites with apical oxygen in the T’structure leads to a variable range-hopping conductivity in the low-spin phase in which the transition temperatureis suppressed under pressure. (Cheng et al., Phys. Rev. Lett., 108, 236403, 2012)

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)