Peak profile fitting in X-ray Crystallography, why Voigt?

[C_Pu]

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?

 

[Andy Resnick]

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?

Gaussian 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]

Gassian lineshapes are due to inhomogeneous broadening mechanisms (Doppler, local strain, etc), while Lorentzian are due to homogeneous broadening mechanisms (collisions, pressure broadening etc).

And is there an explanation for skewness of the peaks?

 

[Andy Resnick]

And is there an explanation for skewness of the peaks?

No clue. Don't know of one.