Effects of Voigt Diffraction Peak Profiles on the Pair Distribution Function

TL;DR

This paper analytically and experimentally investigates how Voigt diffraction peak profiles influence the Pair Distribution Function, revealing their impact on peak shapes and atomic displacement estimations in X-ray scattering analysis.

Contribution

It provides an analytical solution for Voigt peak effects on PDF and demonstrates the importance of correct peak shape modeling in structural refinement.

Findings

Voigt peak profiles produce Voigt-shaped PDF peaks.

Incorrect modeling of Voigt peaks leads to overestimated atomic displacement parameters.

Lorentzian strain broadening significantly affects PDF peak shapes.

Abstract

Powder X-ray Diffraction (PXRD) and Pair Distribution Function (PDF) analysis are well-established techniques for investigation of atomic configurations in crystalline materials, and the two are related by a Fourier transformation. In PXRD experiments, structural information, such as crystallite size and strain, is contained within the peak profile function of the diffraction peaks. However, the effects of the PXRD peak profile function on the PDF are not fully understood. Here, all the effects from a Voigt diffraction peak profile are solved analytically and verified experimentally through a high-quality X-ray total scattering measurements on strained Ni powder. The Lorentzian contribution to strain broadening is found to result in Voigt shaped PDF peaks. Furthermore, it is demonstrated that an improper description of the Voigt shape during model refinement leads to overestimation of the atomic displacement parameter.