Biomedical subjects

Przemyslaw Dera

Publications and source records attributed to Przemyslaw Dera.

4 recordsLinked to original sources

PubMed2005

Single-crystal synchrotron X-ray diffraction study of wüstite and magnesiowüstite at lower-mantle pressures.

This study demonstrates the use of monochromatic synchrotron X-ray radiation of 40 keV for high-precision equation-of-state studies on sets of single crystals analysed individually in the same diamond-anvil pressure cell. Angle-dispersive zone-axis diffraction patterns were obtained from crystals of wustite-Fe0.93O and magnesiowüstite-(Mg0.73Fe0.27)O to 51 GPa in a hydrostatic helium pressure medium. The rhombohedral phase of Fe0.93O was observed above 23 GPa, and its isothermal bulk modulus (K0) was determined to be 134 (+/-4) GPa, assuming K'=4. The rhombohedral phase of Fe(0.93)O is more compressible than B1-structured Fe0.93O, with K0=146 (+/-2) GPa. Magnesiowüstite-(Mg0.73Fe0.27)O remains cubic over the experimental pressure range, and has a bulk modulus of 154 (+/-3) GPa with K'=4.0 (+/-0.1).

Journal Article↗

PubMed2005

Adapting polychromatic X-ray microdiffraction techniques to high-pressure research: energy scan approach.

Polychromatic single-crystal diffraction (pSXD) offers important advantages compared with monochromatic diffraction, such as ultrafast data collection and the ability to collect diffraction data without sample rotation. Despite the relevance of these advantages for applications in high-pressure experiments, pSXD has never been successfully applied for full structure determination at high pressure. Here the theory of polychromatic microdiffraction, strategies developed to adapt it to high-pressure applications, and results of pilot experiments are described. Special emphasis is placed on experiments with microcrystals and multigrain aggregates, and on the use of monochromator scans to extend the pressure range for single-crystal structure determination to the megabar region. Closely related applications to materials research problems are also discussed.

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PubMed2005

Novel chain structures in group VI elements.

Recent developments in high-pressure methods and advances in X-ray crystallography have led to a new level of understanding of phase diagrams and structures of materials under pressure. Recently discovered phenomena such as complex phases of alkali metals, incommensurate host-guest structures, and incommensurately modulated structures have rendered obsolete our conventional wisdom about the range of structures possible in the elements. Using new in situ diffraction techniques, we have resolved the long-standing problem of the phase-transition sequence of sulphur in its non-metallic state. We demonstrate that it is very different from that previously proposed, with only two phases stable between 1.5 GPa and 83 GPa (the pressure of metallization), and temperatures from 300 K to 1,100 K. The phases have a triangular chain and a squared chain structure. The same squared chain structure is found in the heavier group VI element selenium.

Journal Article↗

PubMed2004

Crystal structure of a high-pressure/high-temperature phase of alumina by in situ X-ray diffraction.

Alumina (alpha-Al(2)O(3)) has been widely used as a pressure calibrant in static high-pressure experiments and as a window material in dynamic shock-wave experiments; it is also a model material in ceramic science. So understanding its high-pressure stability and physical properties is crucial for interpreting such experimental data, and for testing theoretical calculations. Here we report an in situ X-ray diffraction study of alumina (doped with Cr(3+)) up to 136 GPa and 2,350 K. We observe a phase transformation that occurs above 96 GPa and at high temperatures. Rietveld full-profile refinements show that the high-pressure phase has the Rh(2)O(3) (II) (Pbcn) structure, consistent with theoretical predictions. This phase is structurally related to corundum, but the AlO(6) polyhedra are highly distorted, with the interatomic bond lengths ranging from 1.690 to 1.847 A at 113 GPa. Ruby luminescence spectra from Cr(3+) impurities within the quenched samples under ambient conditions show significant red shifts and broadening, consistent with the different local environments of chromium atoms in the high-pressure structure inferred from diffraction. Our results suggest that the ruby pressure scale needs to be re-examined in the high-pressure phase, and that shock-wave experiments using sapphire windows need to be re-evaluated.

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