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Investigation of the Surface Stress in SiC and Diamond Nanocrystals by In-situ High Pressure Powder Diffraction TechniqueThe real atomic structure of nanocrystals determines key properties of the materials. For such materials the serious experimental problem lies in obtaining sufficiently accurate measurements of the structural parameters of the crystals, since very small crystals constitute rather a two-phase than a uniform crystallographic phase system. As a result, elastic properties of nanograins may be expected to reflect a dual nature of their structure, with a corresponding set of different elastic property parameters. We studied those properties by in-situ high-pressure powder diffraction technique. For nanocrystalline, even one-phase materials such measurements are particularly difficult to make since determination of the lattice parameters of very small crystals presents a challenge due to inherent limitations of standard elaboration of powder diffractograms. In this investigation we used our methodology of the structural analysis, the 'apparent lattice parameter' (alp) concept. The methodology allowed us to avoid the traps (if applied to nanocrystals) of standard powder diffraction evaluation techniques. The experiments were performed for nanocrystalline Sic and GaN powders using synchrotron sources. We applied both hydrostatic and isostatic pressures in the range of up to 40 GPa. Elastic properties of the samples were examined based on the measurements of a change of the lattice parameters with pressure. The results show a dual nature of the mechanical properties (compressibilities) of the materials, indicating a complex, core-shell structure of the grains.
Document ID
20030062083
Acquisition Source
Marshall Space Flight Center
Document Type
Conference Paper
Authors
Palosz, B.
(Polish Academy of Sciences Warsaw, Poland)
Stelmakh, S.
(Polish Academy of Sciences Warsaw, Poland)
Grzanka, E.
(Polish Academy of Sciences Warsaw, Poland)
Gierlotka, S.
(Polish Academy of Sciences Warsaw, Poland)
Zhao, Y.
(Los Alamos National Lab. NM, United States)
Palosz, W.
(NASA Marshall Space Flight Center Huntsville, AL, United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 2003
Subject Category
Nonmetallic Materials
Meeting Information
Meeting: Materials Research Society Spring Meeting
Location: San Francisco, CA
Country: United States
Start Date: April 21, 2003
End Date: April 25, 2003
Distribution Limits
Public
Copyright
Other

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