ANHARMONIC EFFECTIVE POTENTIAL, LOCAL FORCE CONSTANT AND EXAFS OF HCP CRYSTALS: THEORY AND COMPARISON TO EXPERIMENT

2008 ◽  
Vol 22 (29) ◽  
pp. 5155-5166 ◽  
Author(s):  
NGUYEN VAN HUNG ◽  
TONG SY TIEN ◽  
LE HAI HUNG ◽  
RONALD R. FRAHM
Keyword(s):  
Thermal Expansion ◽  
Fine Structure ◽  
Thermal Expansion Coefficient ◽  
Force Constant ◽  
Expansion Coefficient ◽  
Effective Potential ◽  
X Ray ◽  
X Ray Absorption ◽  
Analytical Expressions ◽  
Good Agreement

Anharmonic effective potential, Extended X-ray Absorption Fine Structure (EXAFS) and its parameters of hcp crystals have been theoretically and experimentally studied. Analytical expressions for the anharmonic effective potential, effective local force constant, three first cumulants, a novel anharmonic factor, thermal expansion coefficient and anhamonic contributions to EXAFS amplitude and phase have been derived. This anharmonic theory is applied to analyze the EXAFS of Zn and Cd at 77 K and 300 K, measured at HASYLAB (DESY, Germany). Numerical results are found to be in good agreement with experiment, where unnegligible anharmonic effects have been shown in the considered theoretical and experimental quantities.

High-order expanded XAFS Debye–Waller factors of HCP crystals based on classical anharmonic correlated Einstein model

2014 ◽  
Vol 28 (21) ◽  
pp. 1450174 ◽  
Author(s):  
Nguyen Van Hung ◽  
Tong Sy Tien ◽  
Ngyen Ba Duc ◽  
Dinh Quoc Vuong
Keyword(s):  
Effective Potential ◽  
Interatomic Interaction ◽  
High Order ◽  
Cumulant Expansion ◽  
X Ray ◽  
Einstein Model ◽  
Atomic Vibrations ◽  
X Ray Absorption ◽  
Analytical Expressions ◽  
Good Agreement

In this paper, high-order expanded anharmonic effective potential and Debye–Waller factors in X-ray absorption fine structure (XAFS) of hcp crystals have been studied based on classical anharmonic correlated Einstein model. Here XAFS Debye–Waller factors are presented in terms of cumulant expansion up to the fourth order and their analytical expressions have been derived based on classical statistical theory. They contain the parameters of a derived high-order anharmonic effective potential that takes into account all nearest neighbors of absorber and backscattering atoms, where Morse potential is assumed to describe interatomic interaction included in this derived anharmonic effective potential. The dependence of the derived cumulants on atomic vibrations is described by their proportionality to the correlated Einstein frequency. This model avoids full lattice dynamical calculations yet provides good agreement of numerical results for Zn and Cd with experiment at several temperatures.

scholarly journals Study the Temperature Dependence of EXAFS Cumulants of Si and Ge by the Anharmonic Correlated Einstein Model

2011 ◽  
Vol 21 (1) ◽  
pp. 25 ◽  
Author(s):  
Vu Van Hung ◽  
Ho Khac Hieu
Keyword(s):  
Fine Structure ◽  
Temperature Dependence ◽  
X Ray ◽  
Einstein Model ◽  
Silicon And Germanium ◽  
Experimental Values ◽  
X Ray Absorption ◽  
Analytical Expressions ◽  
Theoretical Results ◽  
Good Agreement

In present article, the anharmonic correlated Einstein model has been used to study the temperature dependence of Extended X-ray absorption fine structure (EXAFS) cumulants of silicon and germanium crystals. The analytical expressions of the first, second and third cumulants of silion and germanium have been derived. Our numerical calculations are compared with the experimental values and also with other theoretical results showing the good agreement.

Using Variable Temperature Powder X-ray Diffraction To Determine the Thermal Expansion Coefficient of Solid MgO

2007 ◽  
Vol 84 (5) ◽  
pp. 818 ◽  
Author(s):  
Nicholas C. Corsepius ◽  
Thomas C. DeVore ◽  
Barbara A. Reisner ◽  
Deborah L. Warnaar
Keyword(s):  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Variable Temperature ◽  
X Ray Diffraction ◽  
X Ray

Negative thermal expansion in CuCl: An extended x-ray absorption fine structure study

2007 ◽  
Vol 75 (18) ◽  
Author(s):  
M. Vaccari ◽  
R. Grisenti ◽  
P. Fornasini ◽  
F. Rocca ◽  
A. Sanson
Keyword(s):  
Thermal Expansion ◽  
Fine Structure ◽  
Negative Thermal Expansion ◽  
Structure Study ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

Thermal expansion and anharmonicity of solid Kr studied by extended x-ray-absorption fine structure

1997 ◽  
Vol 55 (17) ◽  
pp. 11320-11329 ◽  
Author(s):  
Toshihiko Yokoyama ◽  
Toshiaki Ohta ◽  
Hitoshi Sato
Keyword(s):  
Thermal Expansion ◽  
Fine Structure ◽  
X Ray ◽  
Absorption Fine ◽  
X Ray Absorption

The X-Ray Measurement of the Thermal Expansibility of Al-Si Alloy in the Form of a Cast and a Protective Coating on Steel

2010 ◽  
Vol 163 ◽  
pp. 286-290 ◽  
Author(s):  
Barbara Kucharska ◽  
A. Wróbel ◽  
Edyta Kulej ◽  
Zygmunt Nitkiewicz
Keyword(s):  
Solid Solution ◽  
Thermal Expansion ◽  
Thermal Expansion Coefficient ◽  
Expansion Coefficient ◽  
Protective Coating ◽  
Steel Substrate ◽  
X Ray ◽  
Silicon Crystals ◽  
Standard Value ◽  
Standard Values

The paper presents the investigation of the expansibility of an Al-Si alloy in the form of a protective coating applied on a steel substrate and as a conventional cast, respectively. Examinations were carried out in the temperature range of troom÷220°C using the diffractometric technique based on reflections (311), (222), (400), and (331) from the Al solid solution. It was demonstrated that the coating exhibited better thermal expansibility compared to the cast, and its thermal expansion coefficient was close to the standard values for alloys of the same chemical composition. For the cast, the thermal expansion coefficient was lower by approx. 25% in relation to the standard value. It was also found that the soaking of alloys during X-ray examination reduced their texturing and caused changes in the microstructure of both the coating and the cast by thinning the silicon crystals and rounding their edges.

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