Phonons from neutron powder diffraction

TL;DR

This paper introduces a novel method called dynamics from powder diffraction (DPD) that extracts off-center phonon information from neutron powder diffraction data, enabling phonon-based modeling of the pair density function.

Contribution

The paper presents a new technique to derive off-center phonon information from powder diffraction data, integrating experimental PDFs with theoretical calculations based on interatomic potentials.

Findings

Successfully applied to Ni and CaF2 systems

Enables phonon-based modeling of pair density functions

Provides off-center phonon information from powder neutron diffraction

Abstract

The spherically averaged structure function $\soq$ obtained from pulsed neutron powder diffraction contains both elastic and inelastic scattering via an integral over energy. The Fourier transformation of $\soq$ to real space, as is done in the pair density function (PDF) analysis, regularizes the data, i.e. it accentuates the diffuse scattering. We present a technique which enables the extraction of off-center phonon information from powder diffraction experiments by comparing the experimental PDF with theoretical calculations based on standard interatomic potentials and the crystal symmetry. This procedure (dynamics from powder diffraction(DPD)) has been successfully implemented for two systems, a simple metal, fcc Ni, and an ionic crystal, CaF$_{2}$. Although computationally intensive, this data analysis allows for a phonon based modeling of the PDF, and additionally provides off-center phonon information from powder neutron diffraction.