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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]

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]

X-ray powder diffraction measurements using synchrotron radiation are currently being carried out on three experimental stations on the SRS at Daresbury Laboratory. Station 9.1 contains a general purpose powder diffractometer for angular dispersive measurements. The instrument is sited on the wiggler beamline, which provides radiation with a critical energy of 12 keV. A Si ( 111 ) water-cooled, channel-cut monochromator gives useful flux over an energy range from 6 to 30 keV. A cryostat and furnace are available for experiments requiring special environments, while a curved position sensitive detector can be used for time-resolved measurements. The wiggler white beam is employed on Station 9.7 for energy dispersive powder diffraction experiments. Various sample stages for kinetic experiments are in use on this station, and examples are shown of recent high-pressure work. A new high resolution powder diffractometer has been built and commissioned on Station 8.3, using bending magnet radiation. The diffractometer is based on the Parrish and Hart design, in which long, parallel foils are used to define the angular divergence accepted by the detector. In this way, large synchrotron beam cross sections can be employed while maintaining high angular resolution. [ABSTRACT FROM AUTHOR]