The properties of nanocrystalline materials are critically dependent on the atomic structure of the constituent grains. The tentative model of the materials assumes that the particles constitute a two-phase, core/surface-shell system where the atomic positions at the surface are different than those in the bulk. A conventional diffraction techniques and standard methods of the diffraction data analysis are insufficient to detect small differences between the actual atomic positions in nanograins and those in a regular (unambiguously defined) crystallographic phase; a standard elaboration of the diffraction measurements may readily lead to erroneous interpretations of the experimental results. We have developed a new method of evaluation of nano-powder diffraction data based on the analysis of the shifts of the Bragg reflections from their perfect-lattice positions measured in a large diffraction vector range (Q larger than about 15A-1), we introduced a new variable, "Apparent Lattice Parameter" (ALP), instead of the commonly used average value (lattice constant). The ALP quantities calculated from the actual positions of each individual Bragg reflection plotted versus Q-vector show characteristic features that were used to evaluate the synchrotron X-ray diffraction data of GaN, SiC, and diamond nanocrystals. The analysis of these data shows a strong evidence of the presence of a strained surface shell and of a considerable internal pressure in the nanoparticles. The model of a nanocrystal that combines core and surface-shell phases was found to be consistent with in situ high-pressure (up to 40 GPa) diffraction experiments performed in a diamond anvil cell (DAC). The results of these experiments indicate, that the compressibilities of the surface layers are different than those in the core of the nanograins.

• Legal notice:
  

  Copyright (c) Pielaszek Research, all rights reserved.
  The above materials, including auxiliary resources, are subject to Publisher's copyright and the Author(s) intellectual rights. Without limiting Author(s) rights under respective Copyright Transfer Agreement, no part of the above documents may be reproduced without the express written permission of Pielaszek Research, the Publisher. Express permission from the Author(s) is required to use the above materials for academic purposes, such as lectures or scientific presentations.
  In every case, proper references including Author(s) name(s) and URL of this webpage: https://science24.com/paper/234 must be provided.

1. Analysis of density waves in CdSe, SiC, and diamond nanocrystals by application of NanoPDF software package to experimental Pair Distribution Functions.
2. Looking at the real structure of nanocrystals with powder diffraction: the apparent lattice parameter approach
3. Looking beyond limitations of diffraction methods of structural analysis of nanocrystalline materials
4. Dyfraktometryczna analiza mikro- i makro-naprężeń w spiekach i kompozytach otrzymanych pod wysokim ciśnieniem i wysoką temperaturą.
5. Badania własności termicznych nanokryształów metodami dyfraktometrycznymi
6. Structure of nano-crystals: a key to understanding the unique properties of nano-materials
7. Nanocrystalline SiC compacts obtained by sintering of laser synthesized nanopowders under extreme pressures
8. Synthesis and properties of GaAs nano-composites
9. MD simulation of atomic structure of nanocrystals
10. SiC-Zn nanocomposites obtained using high-pressure infiltration technique
11. Structural and luminescence properties of yttrium-aluminum garnet (YAG) nanoceramics
12. X-ray diffraction studies of thermal properties of bulk- and surface-atoms of nanocrystalline SiC
13. Characterization of nanostructured hydroxyapatite ceramics densified at high-pressure and temperature
14. Powder precursors for nanoceramics: cleaning and compaction
15. Examination of the atomic Pair Distribution Function (PDF) of SiC nanocrystals by in-situ high pressure diffraction
16. Investigation of the microstructure of SiC-Zn nanocomposites by microscopic methods: SEM, AFM and TEM
17. Sythesis of metal-ceramic nanocomposites by high-pressure infiltration
18. X-Ray Characterization of Nanostructured Materials
19. Generetion and Relaxation of Strain in SiC and GaN under Extreme Pressure
20. Influence of high pressure on the polytype structure of nanocrystalline GaN
21. Transformation of fractal microstructure of nanocrystalline SiC and diamond in high pressures - Small Angle Scattering Study