Design of crystal-like aperiodic solids with selective disorder--phonon coupling

TL;DR

This paper introduces a new class of aperiodic solids called procrystalline that leverage correlated disorder to enable unique phonon interactions, potentially enhancing thermoelectric performance.

Contribution

It demonstrates how specific correlated disorder in procrystalline solids can induce selective phonon coupling, challenging the traditional focus on ordered materials for functional properties.

Findings

Identification of procrystalline states and their diffraction signatures

Mapping of these states onto known and target materials

Discovery of disorder-phonon coupling leading to dispersion in phonon energy

Abstract

Functional materials design normally focuses on structurally-ordered systems because disorder is considered detrimental to many important physical properties. Here we challenge this paradigm by showing that particular types of strongly-correlated disorder can give rise to useful characteristics that are inaccessible to ordered states. A judicious combination of low-symmetry building unit and high-symmetry topological template leads to aperiodic "procrystalline" solids that harbour this type of topological disorder. We identify key classes of procrystalline states together with their characteristic diffraction behaviour, and establish a variety of mappings onto known and target materials. Crucially, the strongly-correlated disorder we consider is associated with specific sets of modulation periodicities distributed throughout the Brillouin zone. Lattice dynamical calculations reveal selective disorder-phonon coupling to lattice vibrations characterised by these same periodicities. The principal effect on the phonon spectrum is to bring about dispersion in energy rather than wave-vector, as in the poorly-understood "waterfall" effect observed in relaxor ferroelectrics. This property of procrystalline solids suggests a mechanism by which strongly-correlated topological disorder might allow new and useful functionalities, including independently-optimised thermal and electronic transport behaviour as required for high-performance thermoelectrics.