C_Pu said:Hi,I've been doing a lab cycle on X-ray crystallography. We are using Cu X-ray source on chloride salt crystals. It seems that the Bragg peak profile are commonly acknowledged to be a Voigt function, which is a convolution of Gaussian and Lorentzian. I am wondering what's the physical reason for this. What causes the Gaussian spread and what leads to the Lorentzian component?
And is there an explanation for skewness of the peaks?Andy Resnick said:Gassian lineshapes are due to inhomogeneous broadening mechanisms (Doppler, local strain, etc), while Lorentzian are due to homogeneous broadening mechanisms (collisions, pressure broadening etc).
C_Pu said:And is there an explanation for skewness of the peaks?
Peak profile fitting is a method used to analyze X-ray diffraction data in crystallography. It involves fitting the observed diffraction peaks with a mathematical function to determine the characteristics of the crystal structure, such as unit cell dimensions and atomic positions.
Peak profile fitting is important because it allows for the accurate determination of crystallographic parameters, which are essential for understanding the structure and properties of materials. It also helps to identify and correct for any distortions or imperfections in the crystal lattice.
The Voigt function is a mathematical function that is a convolution of a Gaussian and a Lorentzian function. It is used in peak profile fitting because it provides a good approximation for the diffraction peak shape in X-ray crystallography, which can be a combination of both Gaussian and Lorentzian components.
Peak profile fitting is typically performed using specialized software, such as the FullProf Suite or Topas, which have built-in algorithms to fit the diffraction peaks to the Voigt function. The software takes the observed diffraction data and uses a least-squares fitting method to determine the best fit parameters for the Voigt function.
The Voigt function has several advantages in peak profile fitting, including its ability to accurately model the diffraction peak shape, its robustness against noise and background contributions, and its physical interpretation in terms of the underlying crystal structure. It also allows for the determination of more complex peak shapes, such as asymmetry and broadening due to strain or defects.