Nanokristallerin yapısal analizinde x ışını kırınımı verisinin çift dağılım fonksiyonu (pair distribution function) metodu ile incelenmesi.

Pair Distribution Function analysis is a local characterization method gaining momentum recently. Conventional X-ray diffraction and Rietveld methods have proven not to be accurate in the case of analysis of diffraction data from nanocrystalline powders. In this thesis, we evaluate the accuracy of this alternative technique, which is based on a refinement algorithm in real space, and because of being in real space, the properties obtained from this method are more intuitive. Structural parameters like particle size, neighbor atomic distances, etc. are obtained by directly calculating the distances and area of each peak or distance. Large surface to volume atom ratio is stated to be the reason that makes it hard for conventional X-ray diffractive methods to characterize nanocrystals. Because conventional methods have a fundamental assumption about the materials and that is large crystalline domains in the scattering material. Unfortunately, nanocrystalline powders do not satisfy this assumption. Surface atoms, because of lack of neighbor atoms around them, have a small coordination number, as a result, they do not fulfill crystallinity. However, Pair Distribution Function can obtain the structure of the materials, regardless of their crystallinity. It is claimed that amorphous materials can also be analyzed in this method. The probability of finding two atoms at a special distance from each other, is the basic point of view. This method is being used in different areas of study including drug delivery, materials characterization, fracture mechanics, condensed matter physics, etc. and recently it has been gaining momentum, especially where the conventional diffractive characterization methods cannot have an exact answer for structural properties. Although being a fairly developed algorithm, Pair Distribution Method still needs work to become perfect. For instance, the strain of the particles still cannot be calculated directly in this method, and Diffpy-Complex Modeling Infrastructure is intricate for the ones who are not familiar with object-oriented programming. In this research, we are looking at different approaches towards obtaining the necessary parameters from Pair Distribution Function fitting, goodness of the fits, and validity of the results. The systematic analysis of our work consists of five different nanocrystalline sizes and five different wavelengths, for both ideal nanocrystalline materials and energy minimized nanocrystals in 0 K temperature. The results of Pair Distribution Function show as the nanocrystalline size decreases the amount of crystallinity for the energy-minimized nanocrystals decrease. As the nanocrystals decrease in their size, the obtained values of lattice parameter decrease in comparison with the nominal lattice parameters. Atomic Displacement Parameters for the energy-minimized nanocrystals show a higher value for the smallest nanocrystalline sizes. Also, the predicted nanocrystalline size from this method gives slightly smaller size values which are attributed to the prediction of the peak attenuation. The lowest wavelength X-ray has the highest energy. For the highest energy wavelength, the Pair Distribution Function fit results of the particle size shows the size of the minimized particles is slightly less than the size of the ideal counterparts.