Wyniki wyszukiwania - BazTech

1

Structural Disorder in Quasicrystals

Strzałka R., Bugański I., Śmietańska J., Wolny J.

Archives of Metallurgy and Materials

|

2020

|

Vol. 65, iss. 1

291--294

EN

One of the challenges of modern crystallography of complex systems (complex metallic alloys, proteins, aperiodic crystals and quasicrystals) is to properly describe the disorder in these systems and discuss correctly the refinement results in terms of the structural disorder. In this paper we briefly discuss a new approach to phasons and phonons in quasicrystals and focus on the new theory of phonons in these materials. A newly derived correction factor for phonons in the form of the Bessel function is the approximated way of describing optic modes in the phonon spectra of quasicrystals. It is applied to a real decagonal quasicrystal in the Al-Cu-Rh system with 56/38 atoms per thick/thin structural unit, based on 2092 unique reflections selected from the collected diffraction data, significantly improving the refinement results. The final R-factor value is 7.24%, which is over 0.5% better result comparing to originally reported. We believe our work will open a broader discussion on the disorder in quasicrystals (and other aperiodic systems) and motivate to develop new approaches to treat the diffraction data influenced by different types of disorder in the new way.

2

Algorithms and methods for analysis of the optical structure factor of fractal aggregates

Mroczka J., Woźniak M., Onofri F. R. A.

Metrology and Measurement Systems

|

2012

|

Vol. 19, nr 3

459-470

EN

We introduce numerical methods and algorithms to estimate the main parameters of fractal-like particle aggregates from their optical structure factor (i.e. light scattering diagrams). The first algorithm is based on a direct and simple method, but its applicability is limited to aggregates with large size parameter and intermediate fractal dimension. The second algorithm requires to build calibration curves based on accurate particle agglomeration and particle light scattering models. It allows analyzing the optical structure factor of much smaller aggregates, regardless of their fractal dimension and the size of the single particles. Therefore, this algorithm as well as the introduction of a criteria curve to detect the different scattering regimes, are thought to be powerful tools to perform reliable and reproducible analyses.

3

Dyfrakcja elektronów wstecznie rozproszonych : wpływ struktury materiału oraz parametrów pracy skaningowego mikroskopu elektronowego na jakość obrazów dyfrakcyjnych

Faryna M.

Inżynieria Materiałowa

|

2010

|

Vol. 31, nr 5

1312-1323

PL

W pracy omówiono wpływ szeregu parametrów na jakość obrazów dyfrakcyjnych zarejestrowanych w skaningowym mikroskopie elektronowym zarówno z wysoką, jak i niską próżnią. Najważniejsze parametry to m.in.: atomowy czynnik rozpraszania, czynnik strukturalny, stan sieci krystalicznej, parametry pracy mikroskopu oraz stan powierzchni analizowanej próbki. Obliczono przykładowo czynniki strukturalne dla faz regularnych przestrzennie i ściennie centrowanych. Omówiono znaczenie parametru Ima- ge Quality Factor, który opisuje jakość obrazu dyfrakcyjnego. Podano szereg przykładów analizy tego parametru. Autor zwrócił uwagę na znaczenie odkształcenia sprężystego i plastycznego na jakość obrazu dyfrakcyjnego. Omówił również wpływ rożnych gazów oraz ich zmieniającego się ciśnienia w SEM z niską próżnią na obraz dyfrakcji Kikuchiego oraz powiązał te warunki pracy mikroskopu z rozpraszaniem sprężystym i niesprężystym elektronów wstecznie rozproszonych tworzących stożki Kossela.

EN

The paper summarizes the parameters which affect the quality of Kikuchi patterns acquired in scanning electron microscope operating either in high or low vacuum conditions. Among others things, the most important factors are: atomic scattering factor, structure factor, lattice conditions microscope settings and surface conditions. An example of calculating structure factors for high symmetry structures was also presented. Image Quality Factor as the main parameter describing Kikuchi diffraction was determined and examples of the influence of microscope parameters as well as the sample condition and its preparation on this factor were shown. An application of the EBSD to the analysis of local strains (plastic and elastic) in materials was shortly discussed. Finally, the author draws the readers' attention to the influence of various gases and their increasing pressure in Low Vacuum SEM on the quality of acquired diffraction and correlates this relationship with elastic and inelastic scattering of electrons forming Kossel cones.

4

Structure of decagonal quasicrystals described by clusters

Kozakowski B, Duda M, Wolny J

Materials Science Poland

|

2008

|

Vol. 26, No. 4

903--912

EN

The cluster model offers a new approach to the structure of quasicrystals. The model assumes that the whole structure can be covered by only one structure unit – the cluster. However, because quasicrystals are not periodic, clusters must overlap each other. The first known cluster is G33 proposed by Gummelt. Another type of cluster is the kite cluster – it is the smallest possible cluster that can cover the whole Penrose tiling. There are three different kite clusters: 17-atom K17, 7-atom K7 and 4-atom K4 discussed in the paper.

5

Liquid eutectic alloys as a cluster solutions

Mudry S., Shtablavyi I., Shcherba I.

Archives of Materials Science and Engineering

|

2008

|

Vol. 34, nr 1

14-18

EN

Purpose: In this research work the results of structure studies for Al0.88Si0.12, Bi0.995Cu0.005, Al0.83Cu0.17 eutectic and Co0.05Cu0.95 peritectic melts have been presented. The structure parameters of molten alloys are compared with ones for liquid pure components and with model values. Design/methodology/approach: The structure in liquid state has been studied with use of X-ray diffractometer containing special attachment for investigation of liquid metallic alloys. The system was equipped with special camera for sample, filled with pure helium in order to avoid the oxidation. Experimental data were interpreted with using of random atomic distribution model and self-associated one. Findings: The research has shown that structure of liquid alloys Al0.88Si0.12, Bi0.995Cu0.005, Al0.83Cu0.17 and Co0.05Cu0.95 shows the deviation from random atomic distribution model and these alloys in liquid state at temperatures not far from melting point can be considered as cluster solutions. Practical implications: Existence of clusters in eutectic and peritectic melts influence the structure and properties of corresponding solid alloys, that is important for casting, soldering, welding and at producing of composite materials on the base of eutectic matrix. Originality/value: Cluster structure of eutectic melts is responsible for behaviour of structure and physical-chemical properties. The change of this structure allows to improve the properties of solidificated alloys, both crystalline and amorphous.

6

The structure of liquid eutectic as a gowerning factor in crystallization processes

Prokhorenko W., Mudry S., Prokhorenko S., Bylica A., Navotska J.

Archiwum Odlewnictwa

|

2006

|

R. 6, nr 18/2

527--530

EN

The structure of Ga-In-Sn eutectic melt has been studied by means of x-ray diffraction method. The structure factors and pair correlation functions are analyzed. It is shown that inhomogeneous structure exists within some temperature range and can be changed by outside energetic influence.

PL

W pracy przedstawiono wyniki porównawczych badań stukturalnych eutektycznego stopu Ga-In-Sn. Uzyskane wyniki potwierdziły występowanie w tym stopie struktur niehomogenicznych w szerokim zakresie temperatury oraz możliwość zmiany takich struktur przez zewnętrzne oddziaływanie energetyczne.

7

Molecular dynamics simulation of copolymers

Banaszak M.

TASK Quarterly : scientific bulletin of Academic Computer Centre in Gdansk

|

2001

|

Vol. 5, No 1

17-27

EN

A series of representative molecular dynamics simulations of model Lennard-Jones copolymer chains is presented. We report measurements of thermodynamic, structural and dynamic properties of our model copolymers. For neutral copolymers we confirm our version of thermodynamic perturbation theory of the first order, while for ionic copolymers we demonstrate microphase formation and the anisotropy of the counterion diffusion.