Probing coupling between ‘rattling’ and extended lattice modes using time-of-flight neutron scattering combined with ab-initio calculations—introducing the PALD method

The concept of ‘rattling modes’ has been brought up in the context of several recent studies concerning thermoelectric materials as well as a new class of oxide superconductors. We have initiated projects for the study of such phenomena, with the aim of better understanding of the ‘rattling mode’ scenario and its role in the physical properties in question. The experiments using Time-of-Flight (T-o-F) investigation of polycrystalline samples with optimized resolution are complemented with ab-initio-based phonon calculations, including the powder averaged coherent inelastic response. Accordingly, we can follow the wave-vector transfer dependence of intensities, in consequence the phase coherence of the motion between particular atomic species. The results we have obtained point out the power of the Powder Averaged Lattice Dynamics (PALD) approach using T-o-F experiments. Detailed modeling for this type of study is especially interesting for materials in polycrystalline form and, therefore, well suitable for material science investigations.