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High-resolution x-ray diffraction with diamond-anvil cells, using argon as a quasi-hydrostatic pressure medium, documents the crystal structure and equation of state of osmium to over 60 GPa at room temperature. We find the zero-pressure bulk modulus in fair agreement with other experiments as well as with relativistic electronic band-structure calculations: Osmium is the densest but not the most incompressible element at ambient conditions. We also find no evidence for anomalies in the ratio of unit-cell parameters, c/a, or in the compressibility of osmium as a function of pressure. This is in agreement with other experiments and quantum mechanical calculations but disagrees with recent claims that the electronic structure and equation of state of osmium exhibit anomalies at pressures of ∼15-25 GPa; the discrepancies are may be due to the effects of texturing. [ABSTRACT FROM AUTHOR]

The thermodynamic nature of phase stabilities and transformations are investigated in crystalline and amorphous Ge1Sb2Te4 (GST124) phase change materials as a function of pressure and temperature using high-resolution synchrotron x-ray diffraction in a diamond anvil cell. The phase transformation sequences upon compression, for cubic and hexagonal GST124 phases are found to be: cubic → amorphous → orthorhombic → bcc and hexagonal → orthorhombic → bcc. The Clapeyron slopes for melting of the hexagonal and bcc phases are negative and positive, respectively, resulting in a pressure dependent minimum in the liquidus. When taken together, the phase equilibria relations are consistent with the presence of polyamorphism in this system with the as-deposited amorphous GST phase being the low entropy low-density amorphous phase and the laser melt-quenched and high-pressure amorphized GST being the high entropy high-density amorphous phase. The metastable phase boundary between these two polyamorphic phases is expected to have a negative Clapeyron slope. [ABSTRACT FROM AUTHOR]

We studied the compressibility of monolithic fully dense electrodeposited nanocrystalline Ni (∼29 nm grain size) under both quasihydrostatic and nonhydrostatic conditions up to a nominal pressure of 50 GPa using angle-dispersive x-ray diffraction. We obtained an equation of state consistently and unambiguously from each measured reflection. The apparent bulk modulus measured under nonhydrostatic conditions is larger than that of the corresponding coarse-grained material under either type of compression, but is nearly the same when measured under quasihydrostatic conditions. These results may be consistent with a strength, but not necessarily a bulk modulus, that is enhanced in the nanomaterial relative to its coarse-grained counterparts. [ABSTRACT FROM AUTHOR]

X-ray diffraction measurements of natural talc plus water at combined pressures and temperatures of 0-15 GPa and 23-400 °C reveal the presence of a structural change that could be interpreted as a new high-pressure phase at 4.0 (±0.5) GPa, and raise the possibility that the newly inferred phase transition takes place in cold subducting slabs as a precursor to appearance of the 10 Å phase of talc. [ABSTRACT FROM AUTHOR]

A tensonometer for stretching metal foils has been constructed for the study of strain broadening in X-ray diffraction line profiles. This device, which is designed for use on powder diffractometers and was tested on Station 2.3 at Daresbury Laboratory, allows in situ measurements to be performed on samples under stress. It can be used for data collection in either transmission or reflection modes using either symmetric or asymmetric diffraction geometries. As a test case, measurements were carried out on an 18 µm-thick copper foil experiencing strain levels of up to 5% using both symmetric reflection and symmetric transmission diffraction. All the diffraction profiles displayed peak broadening and asymmetry which increased with strain. The measured profiles were analysed by the fundamental-parameters approach using the TOPAS peak-fitting software. All the observed broadened profiles were modelled by convoluting a refineable diffraction profile, representing the dislocation and crystallite size broadening, with a fixed instrumental profile predetermined using high-quality LaB6 reference powder. The deconvolution process yielded `pure' sample integral breadths and asymmetry results which displayed a strong dependence on applied strain and increased almost linearly with applied strain. Assuming crystallite size broadening in combination with dislocation broadening arising from f.c.c. a/2〈110〉{111} dislocations, the variation of mechanical property with strain has been extracted. The observation of both peak asymmetry and broadening has been interpreted as a manifestation of a cellular structure with cell walls and cell interiors possessing high and low dislocation densities. [ABSTRACT FROM AUTHOR]

The possibility of using X-ray diffraction to precisely monitor crystal structure at the extremes of pressure and temperature produced by shock-wave loading is explored. A summary of the advantages of using various X-ray sources for this work and an outline of the necessary experimental layout is given. [ABSTRACT FROM AUTHOR]

The Advanced Light Source (ALS) is a 1.9-GeV, third-generation synchrotron optimized for the production of VUV and soft X-rays from undulators. There is also a hard X-ray program at the ALS, which is based around three 6-T superconducting bending magnets [1] that shift the critical energy from 3 keV to 12 keV. The extreme conditions beamline at the ALS is situated on Beamline 12.2.2, which benefits from radiation produced by one of these superbend sources. The beamline is designed for X-ray diffraction, X-ray spectroscopy, and X-ray imaging of samples held in diamond-anvil high-pressure cells (DACs). In a DAC, samples are on the order of 10 to 50 μm in diameter and 10 to 30 μm thick and are contained in a metal gasket of typical inner diameters of 100 to 150 μm. For high-quality diffraction patterns with little or no contamination from diffraction from the gasket, the X-ray beam size needs to be on the order of 10 μm × 10 μm. [ABSTRACT FROM AUTHOR]